• Where did the idea of Sociobiology come from?

• What is sociobiology?

• Introduced by E.O. Wilson in 1975 in his attempt to explain social behavior in terms of the reproductive advantages that certain behaviors might have in natural selection.
• The evolution of social behavior and possibility of a biological explanation for human social behavior.

• Individual: simple-minded behavior, not much adaptability, robot-like, each specializes in a small number of tasks.
• Colony: complex behavior, highly coordinated, cooperative

• Impersonal Intimacy
• No individual recognition
• No personal relationships with others in the colony

• Specialization
• Based on division of labor
• Close genetic relatedness with the colony

• What qualities do we associate with social life? 
• Do we find these qualities more in simple organisms or complex organisms?

• Cooperation among individuals
• Altruism
• Cohesion
• These qualities decline in complex organisms

Describe the kittiwake society.

Contrast it to insect social behaviors

• Little cooperation b/w individuals
• Evolved to survive alone
• Look after self offspring
• No efficient division of labor
• No Specialization
• Individuals not as closely related (as insects are)

• Sexual selfishness
• Aggressive males compete to be the dominant animal on the beach
• Compete to pass on genes
• Temporary society

• In mammals, the group is less important than the individual
• Long Memory of events - bonds form
• Jealousy, rivalry, personal recognition - males for females and for offspring
• Typical baboon will join group to benefit in hunting and defense
• Selfish and status-seeking, sexual jealousy
• Life in baboon society is a mixture of mutual cooperation and mutual competition - a strategy to leave more genes
• Communication is more to overcome competition rather than to foster cooperation (as it was in social insects)

• Study of external structure

• Study of internal structure

• Roots
• Stems
• Leaves

• All the roots on a plant make up the plant's root system

• All the stems plus all the leaves on a plant make up the plant's shoot system

• This 2-system arrangement of the vegetative organs reflects the adaptation to a terrestrial habitat
• Where the resources are stratified
• Soil is the source of water and minerals which are absorbed by the roots
• Air is the source of CO2 and light which are absorbed by the leaves

• Differentiate into one of 3 types of tissue classified on the basis of function
• These make up the 3 tissue systems of a plant: dermal, vascular, and ground

Dermal Tissue

• Outside layer(s), protective in function
• I.E. Epidermis in young herbaceous plant parts, cork in older woody plant parts

Vascular Tissue

• In a central core in roots, in vascular bundles in stems and leaves
• I.E. xylem which conducts water and minerals, phloem which conducts food

Ground Tissue

• Fills in the spaces between dermal and vascular
• I.E. Parenchyma often used for storage in roots and stems and for photosynthesis in leaves, collenchyma and sclerenchyma used for support

• Primary functions: anchorage and absorption
• Secondary functions: food/water storage (some roots: i.e. carrots, beets, radishes, turnips, sweet potatoes)

• Primary: 1st root to develop when a seed germinates, develops from the radicle of the seed
• Secondary: Aka branch or lateral roots: develop from primary root
• Adventitious: develop from some non-root tissue: i.e. from stem or leaf tissue, such as roots that develop from cuttings that are placed in water to root, also prop roots for support

• Taproot system
• Fibrous (or diffuse root system)

• Has one main root, the primary root remains prominent, none of the secondary roots grow as large as the primary root 
• Characteristic of dicots (one of the groups of flowering plants)

• Consists of a cluster of roots, all of which are about the same size, the primary root has been overgrown by secondary roots
• Characteristic of monocots (the other group of flowering plants

• Annual
• Biennial
• Perennial

• Live for one growing season
• Whole life cycle (vegetative and reproductive) completede in one season

• Live for 2 growing seasons
• Typically, the 1st season is vegetative and the 2nd is reproductive

• Live for 3 or more (sometimes many more) growing seasons

• Longitudinal section of a root tip shows 4 regions or zones
• Root cap
• Zone of cell division (apical meristem)
• Zone of elongation 
• Zone of maturation (root hair region)

• A region of loosely organized cells at the tip, covering and protecting the apical meristem
• Root cap cells are constantly being worn away as the root pushes through the soil
• Cells from the meristem replace the root cap cells that wear away

• Above the root cap
• Here, cells are constantly dividing and producing additional cells which results in growth in length 
• Root grows from the tip down

• Above the apical meristem
• Here, cells stop dividing and begin to enlarge and elongate, primary (intermediate) meristems
• Called protoderm, procambium, and ground meristem
• Develop in this region

• Also called the root hair region
• Above the zone of elongation
• Here, the primary meristems mature and differentiate into dermal, vascular, and ground tissues
• Numerous root hairs which greatly increase the absorptive area of the root are found in this region

3 distinctive differences of

root hairs with secondary roots

• Root hairs: Unicellular, short-lived, develop from epidermis

• Secondary roots: Multicellular, long-lived, develop from inside the root (from the pericycle)

• The outer protective layer of cells

• A region composed of many layers of loosely-packed, thin-walled parenchyma cells
• in food storage roots, starch grains are found in these cells

• A single layer of tightly-packed, thick-walled cells making up the inner boundary of the cortex
• The wall thickenings (called casperian strips) function to prevent passage of materials b/w endodermal cells and ensure that materials pass through endodermal cells

• The central cylinder
• consisting of pericycle, xylem, phloem, and vascular cambium

• A potentially meristematic layer just inside the endodermis, pericycle produces secondary roots

• Thick-walled water-conducting cells

• Thinner-walled food-conducting cells

• Found between the xylem and phloem
• Non-functional in young herbaceous roots

• Conduction of water and minerals upward and conduction of food downward
• Support of leaves and flowers

• Food/water storage
• Some stems grow underground and are highly modified in structure and specialized in function

Specialized functions of

secondary underground stems

• Horizontal underground rhizomes which are found in ferns, irises, and many grasses, and which help to spread the plant horizontally
• Tubers are the short, thickened, terminal portions of rhizomes in which food is stored, such as an Irish potato
• Bulbs are enlarged fleshy underground buds that store food, such as an onion

• Stolons (commonly called runners), which are horizontal stems that grow along the surface of the soil 
• Thorns on a honey locust which are protective in function

• Terminal (apical) bud
• Lateral (axillary) buds
• Bud scale scars
• Leaf scars
• Vascular bundle scars
• Lateral bud scars
• Lenticels
• Nodes 
• Internodes

• Found at the tip
• Consists of a mass of apical meristem
• Usually covered and protected by overlapping bud scales
• Terminal buds contain immature shoot tissue and upon becoming functional, they produce additional growth of the stem lengthwise
• Thus, they are the growing point of the stem as far as length is concerned

• Found along the sides of the stem and silmilar in structure to the terminal bud, but smaller
• The name axillary refers to the location of these buds in the axil between the stem and a leaf
• Some of these will not develop and will eventually drop off the stem, those that do develop produce side branches
• Side branch development is stimulated by the death or removal of the terminal bud
• This principal is put to practical use in pruning to control the shape of the plant
• I.e. a tall, spindly plant can be stimulated to "brush out" by removing some of the terminal buds
• Other reasons for pruning are to remove dead or diseased wood and to restore the shoot/root balance after transplanting

• Clusters of horizontal slit-like scars that encircle the stem at various intervals 
• These scars are produced when the bud scales drop from a terminal bud at the beginning of a growing season
• Thus, the number of these scars can be used to determine the age of the stem externally

• Found immediately below a lateral bud (or lateral bud scar)
• Represents the location of a leaf during a previous growing season
• Leaf scars vary in size and shape and often can be used in the identification of a plant

• Small dot-like scars on the surface of a leaf scar
• Bundle scars represent the broken ends of vascular bundles (strands of vascular tissue) that passed from the stem into the leaf

• Found on the sides of the stem wherever a lateral bud has dropped off

• Small pores on the surface of the stem that allow for exchange of oxygen and carbon dioxide b/w the stem and the atmosphere

• Places on the stem where leaves are produced

• Regions of the stem between 2 successive nodes

• Herbaceous: soft, green, short-lived, cambium is not functional -  therefore, no secondary growth occurs

• Woody: Hard, brown, long-lived, cambium is functional - therefore, secondary growth occurs

Internal structure of an

herbaceous dicot stem

• Epidermis
• Cortex
• Pith
• Vascular bundles: composed of xylem and phloem

Epidermis of an

herbaceous dicot stem

• The outermost protective layer

• Region immediately inside of the epidermis, composed mainly of thin-walled parenchyma with a smaller amount of thick-walled collenchyma in patches just inside the epidermis

• Region in the center of the stem, also composed of parenchyma

Vascular bundles of an

herbaceous dicot stem

• Arranged in a ring (this is characteristic of dicots), composed of:
• Xylem: larger, thick-walled cells, located toward the insie of the stem
• Phloem: smaller, thinner walled cells, located toward the outside of the stem

Internal structure of an

herbaceous monocot stem

• Epidermis
• Parenchyma
• Vascular bundles: composed of xylem, phloem, and sclerenchyma sheath

Epidermis of an

herbaceous monocot stem

• The outermost protective tissue

• Filling tissue that surrounds the vascular bundles

Vascular bundles of an

herbaceous monocot stem

• Scattered throughout the stem (this is characteristic of monocots): composed of 
• Xylem: larger, thick-walled cells
• Phloem: smaller, thinner walled cells
• Sclerenchyma sheath: a supportive layer surrounding the bundle

• Primary function is photosynthesis
• Some leaves have secondary functions such as: food/water storage, protection and water conservation (cactus spines support) or (tendrils on climbing plants)

• Leaf parts
• Leaf venation
• Leaf composition
• Leaf arrangement
• Leaf duration

• Blade: the thin, flat, expaned portion of the leaf
• Petiole: the stalk that attaches the blade to the stem
• Leaves w/o a petiole are called sessile leaves
• Some leaves have a pair of bract-like appendages called stipules at the base of the petiole, these may be vestigial structures since leaves w/o stipules have survived very well

• Arrangement of the veins (vascular bundles)
• Net venation 
• Parallel venation

• Veins branch and rebranch into smaller and smaller veins forming an interconnected network which supplies the entire blade with vascular tissue
• characteristic of dicots
• 2 types: pinnate and palmate

• Pinnate: one main vein (midrib) down the middle of the blade, smaller veins branch off
• Palmate: several main veins grown from a common point at the tip of the petiole, smaller veins branch off

• Veins run parallel to each other throughout the length of the blade
• Do not form an interconnected network
• Characteristic of monocots

• Simple: blade is in one piece, not subdivided into leaflets
• Compound: blade is subdivided into smaller segments, called leaflets
• Pinnately compound: leaflets are attached on either side of an elongated stalk (the extended petiole)
• Palmately compound: leaflets are attached at a common point at the tip of the petiole

Leaf arrangement

• Refers to the number of leaves per node
• Alternate: 1 leaf per node
• Opposite: 2 leaves per node
• Whorled: 3 or more leaves per node

• Deciduous: Leaves live for 1 growing season
• Evergreen: Leaves live for 2 or more growing seasons - but they do not all drop off the tree at the same time, therefore the tree is evergreen

• Cuticle
• Upper epidermis
• Mesophyll
• Veins
• Lower epidermis
• Stomata

• A thin, waxy, nonliving secretion of the epidermis
• found more commonly on the upper epidermis

• The single layer of protective tissue on the upper side of the leaf

• 2 layers of parenchyma (ground tissue) located between the upper and lower epidermis
• Palisade parenchyma: elongated, tightly packed cells, adjacent to the upper epidermis
• Spongy parenchyma: irregularly shaped loosely packed cells, adjacent to the lower epidermis, contains numerous intercellular spaces

• Vascular bundles interspersed throughout the mesophyll
• composed of xylem and phloem

• The single layer of protective tissue on the lower side of the leaf

• Pores in the epidermis
• Found more frequently in the lower epidermis
• The size of the pore is controlled by changes in the size and shape of the 2 guard cells on either side

Macronutrients

• Carbon, oxygen, hydrogen: obtained from CO2 and H2O: these are the major components of the plant's organic compounds
• Nitrogen, phosphorus, potassium, calcium, magnesium, sulfur: mineral nutrients obtained from soil calcium and magnesium are plentiful in most soils, fertilize to add the others
• Nitrogen, phosphorus, potassium are required in the greatest amounts: commercial fertilizers are rated by the % of these 3

• Produced by weathering of rock and decomposition of organic matter

• Minerals
• Soil water
• Organic matter
• Living organisms
• Oxygen

• From rock breakdown, type of rock determines what minerals are present

• Size of soil particles affects capacity to hold water: smaller particles (such as clay) hold more water (more spaces, more surface area), larger particles (such as sand) do not hold water as well
• best soil is a mixture of sizes
• Soil water contains dissolved molecules and ions, some tightly bound to soil particles b/c of charge on particles and ions: cation exchange helps make these nutrients available
• soil pH determines what is dissolved and thus available to plants, most plants do best between pH 6.0 and 7.5
• To adjust soil pH, add lime to raise pH, add sulfur or ammonium sulfate to lower pH (chemicals also add nutrients)

• Also called humus
• Soaks up water and releases it later as neeed
• Also helps to keep the soil loose
• Organic mulch on top of soil acts as a sunscreen and as a reservoir of nutrients which are released slowly
• Thus organic matter is better than commercial fertilizer b/c organic matter provides soil conditioning and slow release of minerals prevents fertilizer burn

• Numerous and varied
• I.e. bacteria and fungi (decomposers), worms, insect larvae

• Important for respiration of roots and soil organisms
• Earthworms are natural cultivators, mixing air with soil particles

Transport in plants

at the cellular level

• Diffusion: movement of molecules from a region where they are more concentrated to a region where they are less concentrated
• Osmosis: diffusion of water through a differentially permeable membrane from a region where it i more concentrated into a region where it is less concentrated
• Active transport: movement of molecules from a region where they are less concentrated ino a region where they are more concentrated: this requires energy

Transport in plants

at the tissue and organ level

• Cell wall pathway
• Cytoplasmic pathway, through the plasmadesmata

Transport in plants

at the whole plant level

• This involves the vascular tissues
• Bulk flow: movement due to pressure differences moves water and minerals through xylem and food through the phloem

• Absorption of water and minerals by roots and lateral transport through the root

• Pipelines of cells stacked one on top of another
• The ascent of water and minerals (sap) in xylem vessels
• 3 factors: capillarity, root pressure (the push from the bottom), transpiration (the pull from the top)

• movement of fluid into a narrow tube b/c of the attraction of the walls of the tube for the molecules of the fluid (adhesion) 
• Molecules of water adhere to the sides of the tube and these water molecules pull other water molecules up (cohesion)
• By capillary alone, water can rise only a few feet (2-5 ft)
• So if the sap cannot climb on its own, it must either be pushed from the bottom or pulled from the top

• The push from the bottom
• Root pressure results from the active transport of ions followed by osmosis of water
• Thus building up hydrostatic pressure in xylemt
• This can be demonstrated in some plants by cutting off the plant near the ground, sealing the stump in a glass tube and watching the sap rise in the tube
• In small plants guttation (loss of liquid water from leaves) may occur as a result of root pressure
• Greatest root pressures measured can push sap only a few feet
• Thus capillarity and root pressure alone are not sufficient to account for movement of sap in large plants

• The pull from the top
• Loss of water vapor (by evaporation) from pores in the leaves
• Experiment to show this: Cut leafy branches from a plant, remove different amounts of leaves from them, put them in containers of water and observe that the amount of water lost from the containers is directly proportional to the area of leaf surface on the branch

The sequence of events

that moves the sap upward

• Transpiration
• Cohesion
• Tension

• The leaf water evaporates from mesophyll cells into the air spaces and from there out through stomata
• Loss of water creates a water deficit in cells next to the air spaces
• This lost water is replaced by water from neighborhood cells
• Then these cells get replacement water from neighboring cells, etc
• Eventually, water lost from mesophyll cells is replaced by water from xylem in the leaf
• From xylem in the stem
• And so on down to the root, and then to the soil

• Continuance of Transpiration: and then to the soil
• since water molecules stick together
• Pulling water out the top of a xylem column is like pulling on a thin thread of water that extends all the way down the xylem pipeline

• Transpiration sets this process in motion and cohesion of water molecules allows it to continue
• Hence it is called the transpiration-cohesion-tension mechanism of water transport

Transpiration-Cohesion-Tension

Mechanism

• Evaporation of water from the upper plant (transpiration)
• Creates a negative pressure (tension)
• In xylem that pulls water molecules from the lower plant (by cohesion)

• Moves water up from the roots, through the xylem, and out through the stomata
• Water lost from the leaves is continuously replaced as soil water is taken up by the roots

Factors of the

rate of transpiration

• Structural factors: density of stomata, thickness of cuticle
• Environmental factors: availability of soil water, temperature, humidity, wind, and sunlight (stimulates photosynthesis in guard cells, causing them to build up sugar and thus take up water and become turgid, opening the stoma)

• Movement of sugars (and other nutrients) in phloem following a source to sink pathway 
• source - where sugar is produced, i.e. leaves
• sink - where sugar is not produced and has to be imported, i.e. roots

Pressure flow

hypothesis

• Solutes move in solutions that move b/c of differences in water concentration (pressure) caused by differences in solute concentration
• Sugar from mesophyll is transported into sieve tubes which causes water to be drawn into sieve tubes by osmosis
• Added water causes turgor pressure to increase, forcing fluid through the sieve plates toward the roots
• In the roots, sugar is removed from sieve tubes and either used or stored as starch
• Water moves out of sieve tubes by osmosis
• Thus, water flows in at one end of the sieve tube and out at the other - b/w the 2 points, water and solutes move by bulk flow

• Primary and seconday growth results from the functioning of meristematic tissue

• Perpetually young tissue, retains the ability to continue dividing
• Apical Meristem: found at the tips of roots and stems, responsible for growth in length - this is also called primary growth
• Lateral meristem: found as layers of cambium (vascular cambium and cork cambium) inside of roots and stems, responsible for growth in diameter - this is also called secondary growth (not all plants have secondary growth

Internal structure of a 

woody dicot stem

• cork
• cork cambium
• cortex
• secondary phloem
• vascular cambium
• secondary xylem
• pith

• Several layers thick
• a dermal protective tissue that has replaced the epidermis

• Just inside the cork
• Produced the cork

• Inside the cork cambium
• Composed mainly of parenchyma

• The largest area of the stem
• Made up of a number of anual rings equal to the number of years the stem has lived (this is what you are counting when you count the rings in an old tree stump)
• Each ring consists of a light band of spring wood toward the center of the stem and a darker band of summer wood toward the outside, making it easy to see where one ring stops and the next one starts

• Inside the cortex
• Has been produced by vascular cambium

• Layer of lateral meristem between the secondary phloem and secondary xylem

• In a young woody stem, there is still some pith parenchyma in the center of the stem
• This decreases each year as the secondary xylem increases 
• The pith eventually disappears in an older stem

• Everything from the vascular cambium out is the bark
• Everything from the vascular cambrium is in the wood

In older

woody stems..

• The xylem in the center of the stem stops conducting water and minerals and turns dark due to the accumulation of waste products
• This is called heartwood, the lighter colored wood outside of that continues to ocnduct water and minerals and is called sapwood

Alternation of 

Generations

• Ferns and flowering plants

2 types of reproduction

in flowering plants

• Vegetative
• Sexual

Vegetative reproduction 

in flowering plants

• An extension of the kinds of growth already discussed
• Gives rise to new individuals with geneti make-up identical to parent plant, thus perpetuating gene combinations that are well adapted to a particular environment
• i.e.: root cutting, separate bulbs, cut up tubers

Sexual reproduction

in flowering plants

• Involves fertilization and meiosis
• Involves production and growth of the flower, production, fertilization of gametes and development of embryo, seed, and fruit
• Advantages: New genetic combinations in each generation, Production of seeds which can disperse over a wide area and which are protected against adverse environmental conditions

• Sepals
• Petals
• Perianth
• Stamens
• Carpel

• Usually small and green
• Collectively called the calyx

• Usually larger than the sepals
• Some color other than green
• Collectively called the corolla

• Sepals and petals collectively
• Functions: protection of reproductive parts (especially in the bud stage), attraction of insects which led to insect pollination which is thought to be the main factor that has allowed angiosperms (flowering plants) to become more successful than gymnosperms

• Male reproductive structures
• Consist of filament (the stalk) and anther (produces the pollen grains)(the young male gametophyte bodies)

• Also called a pistil
• Female reproductive structure
• Consists of: stigma (upper part, where pollen grains germinate), style (the neck or stalk), ovary (the enlarged basal part where the ovule (immature seeds) which contain the female gametophyte are produced)

Variations in 

flower structure

• Complete flower
• Incomplete flower
• Perfect flower
• Imperfect flower

• has all 4 parts
• sepals, petals, stamens, carpel (pistil)

• any one of the 4 types is missing

• has both the reproductive parts
• stamens and carpel (pistil)

• either of the reproductive parts is missing
• Thus imperfect flowers are either male or female
• If both male and females flowers are on the same plant, the plant is monoecious
• If male and female flowers are on different plants, the plant is dioecious

Variations in number

of flower parts

• Monocots have flower parts in 3s or multiples of 3
• Dicots have flower parts in 4s or 5s or multiples of 4 or 5

Male development 

of the gametophytes

• Inside the anthers, meiosis produces microspored which develop into pollen grains containing 2 sperm
• pollen grains will produce pollen tubes after being transferred (by wind, insects, birds, bats) to a stigma
• Pollen grain plus pollen tube makes up the mature male gametophyte body

Female development

of the gametophytes

• Inside the ovules in the ovary
• Meiosis produces megaspores
• One of which will develop into the female gametophyte
• Called an embryo sac or egg sac which produces an egg and 2 polar nuclei

• Transfer of pollen from an anther to a stigma where it germinates to form a pollen tube

Pollen tube

• Carrying 2 sperm
• Grows through the style to the ovary
• Grows into the ovule and discharges the sperm in the embryo sac
• This leads to double fertilization (only in the angiosperms)
• 1 sperm fertilizes the egg producing the zygote
• The other sperm fuses with the 2 polar nuclei producing the endosperm
• Then the zygote develops into an embryo, the endosperm develops into food storage tissue, and the outer layer of the ovule develops into a seed coat
• Thus, an ovule has developed into a seed (a seed consists of a dormant embryo, a food storage region, and a seed coat)

• Consists of:
• cotyledons: one in a monocot seed and 2 in a dicot seed: which are also food storage areas
• epicotyl: the embryonic stalk above the point of attachment of the cotyledons
• hypocotyl: the embryonic stalk below the point of attachment of the cotyledons
• Plumule: at the tip of the epicotyl, grows into the shoot of the new seeding
• Embryonic root (radicle): at the tip of the hypocotyls, grows into the root of the new seeding
• the ovary then develops into a fruit

• The resumption in growth of the seed after a period of dormancy

Plant growth

regulators (hormones)

• Every aspect of the production, differentiation, growth, and maturation of plants is regulated by chemicals - the plant hormones
• Environmental stimuli affect the production and distribution of hormones - the hormones in turn govern responses by which the plant adapts to these external factors

• Chemical messengers produced in one part of an organism and transported to other parts where they exert an effect

Differences in plant

and animal hormones

• Plants do not have distinct hormone-producing glands (endocrine glands) as animals do - rather plant hormones are produced in various organs that have other functions as well: i.e. roots, stems, leaves
• Plant hormones can affect virtually any tissue in the plant, rather than having specific target tissues as animal hormones do
• Plant hormones usually do not maintain homeostasis (as many animal hormones do) - but instead affect changes, such as growth, differentiation, and responses to the environment

5 major plant

hormones

• Auxins
• Cytokinins
• Gibberellins
• Abscisic acid
• Ethylene

• 1st plant hormones discovered, functions include: 
• Promote meristematic growth and cell elongation
• Prevent leaves, flowers, and fruits from falling off prematurely
• In apical buds - partially responsible for apical dominance
• Phototropism: auxin causes stems to bend toward light (b/c auxin is light sensitive, it accumulates on the darker side of the stem, causing it to grow faster, thus bending the plant toward the light)
• Gravitropism: Auxin causes roots to grow down and shoots to grow up
• Synthetic auxins are used commercially in rooting preparations and as weed killers (2,4-D)

• Functions include: 
• Stimulate cell division
• Inhibit aging of leaves: florists spray cut greenery and flowers with cytokinin to keep them fresh
• Interact with auxin to produce the total growth pattern of the plant

• Functions include:
• Promote stem elongation
• Stimulate leaf and flower growth: florists use to stimulate early flowering

• Functions include: 
• Inhibition of growth (it opposes the 3 growth-promoting hormones)
• Promotes dormancy in shoots and seeds
• Promotes closing of stomata during water stress

• Functions include:
• Fruit ripening
• Counteracts some of the effects of auxin (acts as a check and balance system)
• Promotes dropping of leaves, flowers, and fruits

• Growth responses in the direction of environmental gradients, tropisms orient the plant favorably with respect to the resources it needs
• Phototropism: response to light
• Gravitropism: response to gravity

• Response to length of day and night
• Short-day plants
• Long-day plants
• Day-neutral plants

• flower only if exposed to light for less than a certain maximum amount of time each day 
• i.e. tobacco, soybeans, rice

• Flower only if exposed to light for more than a certain minimum amount of time each day, 
• i.e. spinach, radish, barley

• Flower at a certain stage of growth regardless of day length
• i.e. tomatoes, cucumbers

How do plants measure

the length of the photoperiod?

• The pigment phytochrome has 2 different chemical forms that change in response to exposure to different wavelengths and amounts of light
• Flowering apparently depends on phytochrome being in the proper form for a certain length of time during the right part of the plant's daily cycle

Barry Commoner's 4

basic laws of ecology

• Everything is related to something else
• Everything is going someplace
• There is no such thing as a free lunch
• Nature knows best

Hierarchy of organizational

levels in the ecological world

• Population
• Community
• Ecosystem
• Biome
• Biosphere

• a group of interbreeding individuals of the same species, living in the same geographic area

• 2 or more populations of different species, living in the same geographic area and interacting with one another

• A community of living organisms plus their non-living environment through which energy flows and minerals cycle

• A groups of ecosystems with common patterns of climate and distinctive vegetation distributed over a wide area

• All of the ecosystems of the world
• The portion of the earth that supports life, including the atmospher (air), the hydrospher (water), and the lithosphere (land)

• A large terrestrial geographic region containing distinctive plant communities
• A group of communities of organisms with common patterns of climate (temperature and precipitation) and distinctive vegetation, distributed over a wide area
• Thus, areas with similar climate have similar plant communities

Temperatue and 

Precipitation

• The 2 main climatic factors which determine the distribution of biomes are temperature and precipitation
• Generally speaking: the higher the temp and the higher the rainfall in an area, the more and larger plants it can support

• Communities that make up biomes are discontinuous
• But resemble each other in different parts of the world
• Thus, a biome is a class or category, not a specific place
• Obviously, the boundaries are not as sharp as they appear on the map
• There are transition zones

• Biomes are the largest easily recognizable subdivisions of the biosphere
• Each biome is characterized by a general type of plant/animal community which looks much the same wherever the biome occurs, even though the particular species vary from place to place
• A particular biome wherever found in the world has been shaped by a particular combination of topography and climate, therefore even though species differ from place to place, each biome has a characteristic appearance b/c the plants and animals have adapted in similar ways to a particular environment (convergent evolution)

• A biome is sometimes viewed as a very large ecosystem
• But it is more accurate to view it as a collection of similar and related ecosystems
• Each biome consists of a number of ecosystems which are related to each other more closely than they are to the ecosystems making up other biomes

• Found in the arctic regions of North America and Eurasia
• Long extremely cold winters, summers are only a few weeks
• Permafrost (permanantly frozen subsoil) prevents penetration of water and plant roots, therefore vegetation is sparse
• Dominant plants are lichens, mosses, sedges, grasses, low growing shrubs
• Dominant animals are caribou, musk ox, wolverine, artic fox: many have heavy fat or fur layers, some change color in winter
• Food chains are simple and limited, populations may show extreme fluctuations in #s 
• Organic decomposition is slow because of extreme cold, thus soil builds up slowly
• Southern extensions in N. America are found as alpine tundra in high mountainous regions of more temperate zones

• Also called the taiga
• Found across N. America and Eurasia south of the tundra w/ southern extensions in mountainous regions such as the Cascades, the Sierra Nevada, and the Rockies
• Summers cool, Winters cold
• Rainfall moderate, soil thin and nutrient-poor
• Dominant plants are pine, spruce, fir (different species in different areas): forest floor is shaded year-round, thus the ground is somewhat bare
• Dominant animals are squirrel, beaver, porcupine, deer, moose, black bear

Moist temperate

coniferous forest

• Also called temperate rain forest
• moderate coastal climate: Alaska to northern California
• Cool summers with abundandt rain and fog
• I.e. redwood forest in CA and Olympic rain forest in Washington (spruce and fir)
• Understory is well-developed where light penetrates
• Dominant animals are similar to northern coniferous forest

Eastern Deciduous

Forest

• also known as a Temperate deciduous forest
• eastern U.S. (includes Memphis)
• Moderate Temperatures w/ distinct seasons
• abundant year-round precipitation
• Dominant plants are bread leaf deciduous trees - species composition varies in different areas: i.e. beech/maple, maple/basswood, oak, oak/hickory, mixed species
• Dominant animals are black bear, white-tailed deer, raccoon, gray squirrel, insects, birds in eastern U.S., only .5% of original deciduous forest remains undisturbed

• Found on all continents except Antarctica normally occupies interior of continent where rainfall is relatively light - too dry to support a forest, but too wer to be a desert
• W/ light rainfall, nutrients are not leached from the soil - thus it is very fertile - this is the best agricultural land
• Dominant plants are grasses - tall grasses in the prairie in the more eastern part of the grassland and short grasses in the drier plains further west
• Dominant animals are pronghorn antelope, prarie dog, coyote, badger prairie chicken, bison 

Tropical savanna 

(Tropical grassland)

• Only major biome not represented in N. Amer.
• Found in warm regions w/ prolonged dry seasons and recurrent fires - largest one is in Africa, also in S. America and Australia
• Dominant plants are grasses w/ a few small scattered shrubs or trees
• Dominant animals are hoofed grazing mammals such as giraffe, antelope, wildebeest, zebra, and their predators, lion and cheetah

• Found in S. California and the Mediterranean
• Temperate coastal areas w/ mild, rainy winters and long, not, dry summers (often called a "Mediterranean climate")
• Dominant plants are spiny evergreen shrubs adapted to and often dependent on periodic fires - some produce seeds that will germinate only after exposure to fire, some sprout from fire-resistant roots after fires - thus, fire maintains the vegetation
• Dominant animals are coyote, gray fox, mule deer, ground squirrel

• Found in regions characterized by dry, sub-tropical air masses, such as the Sonoran Desert in the southwest U.S. and the Sahara Desert in Africa
• Other temperate deserts or "cool deserts" are found in the rain shadow east of mountain ranges such as the Cascades and the Sierra Nevada which block the coastal moisture from reaching the Great Basin region of Washington, Oregon, Utah, and Nevada - more brush and perennial grasses are found here that in hot deserts
• Dominant plants in hot deserts are cacti, adapted to gather and conserve what little water is available - reduced leaf surfaces, thick succulent stems
• Many animals such as reptiles and rodents conserve water by being nocturnal 

Tropical Rain 

Forest

• Found in equatorial Central and S. America, Africa, and southeast Asia where rainfall and temperatures are high throughout the year
• Richest biome in species diversity
• Rapid plant growth due to excellent growing conditions year-round (temp., rainfall, and light), also organic decomposition is rapid, thus minerals are recycled quickly
• Dominant plants are tall trees with slender trunks, branching near the top, forming a dense canopy over a thick understory of vines, ferns, and epiphytes such as orchids and bromeliads - much growth is stratified with distinct levels
• Animals are diverse and colorful, including birds, amphibians, mammals, reptiles, insects - many are aboreal

Effects on vegetation

from latitude and altitude

• Increasing latitude and altitude have similar effects on the changes in vegtation going north from the equator to the pole or going from the base to the top of a mountain
• You would see similar changes in the vegetation which result from decreasing temperatures and decreasing amounts of available moisture

• Strictly speaking, the term biome refers to terrestrial communities - however, we can stretch the meaning  of the term a bit and apply it to aquatic communities b/c there are many aquatic communities, both freshwater and marine, which exhibit similarities wherever in the world they occus 
• And as on land, environmental conditions influence the distribution of organisms in water
• i.e. temp, nutrient supply, intensity of sunlight, salinity, wave action, water currents

• Except in very shallow lakes, there is a vertical stratification of the physical and chemical variables which affect life in the lake
• 3 of these variables are: sunlight, dissolved oxygen, and temperature

• The source of energy for photosynthesis - thus, this is critical in determining what will survive in the lake - both the plants and animals which depend on the plants for food
• The intensity of light decreases with depth
• The upper zone where there is sufficient light for photosynthesis is the photic zone - here plants produce more oxygen than they use so extra is available for respiration of other organisms
• Below that is the aphotic zone where there is not enough light for photosynthesis
• The "dividing line" b/w these 2 zones is the compensation depth - where the available light is just enough for photosynthesis and respiration to balance each other (in green plants) - the level of this depth depends on the clarity of the water
• The littoral zone is the shallow, well-lighted water around the edge of the lake - here there are rooted aquatic plants such as water lillies, willows, and rushes - in many lakes photosynthesis in this zone provides most of the lake's productivity - fish, tadpoles, insects, snails, worms, etc. feed among these plants
• The limnetic zone is the well-lighted open surface of the lake - here there are floating plants, algae (photoplankton) and animals such as fish, small arthropods, and zooplankton

Dissolved Oxygen

• This affects many aspects of life in the lake, including what can live where and the solubility of many nutrients
• Oxygen enters the water from photosynthesis and by dissolving from the atmosphere at the surface (thus, it is more abundant in the upper photic zone) and is removed from the water by respiration - large amounts of oxygen are used by the bacteria that decompose the detritus (dead organic matter) that settles to the bottom.

• Temperature has a profound effect on the seasonal activities of a lake - this is due to the fact that water (which has a freezing point of 0 degrees C) has a peculiar property of being most dense at 4 degrees C - and therefore will sink below the water that is either warmer or colder, resulting in a mixing of the lake water twice a year
• In winter - at 0 Degrees C the surface freezes, while under the ice the water remains between 0 and 4 degrees C and the lake's organisms survive w/o freezin
• In spring - the ice melts as the sun warms the surface - when the surface water reaches 4 degrees C, it sinks thus forcing the colder water below to rise to the surface - this is the spring overturn which is important b/c it brings nutrients up and carries Oxygen down
• In summer - another temperature stratification occurs as the colder (4 degree) denser water gets trapped below the warmer water on the surface
• In fall - another overturn - the fall overturn - occurs as the surface water cools - when it reaches 4 degrees it sinks below the warmer water just under the surface - as in the spring, this is important to the life in the lake b/c it brings nutrients up and carries oxygen down

2 Kinds of Lakes 

(based on productivity: 

how much plant 

life they support)

• Eutrophic: relatively shallow, rich in organic matter and nutrients, very productive, but contains little oxygen because decomposers use it up rapidly
• Oligotrophic: deeper, poor in nutrients and therefore little productivity, little organic material, but contains more dissolved oxygen b/c there are fewer decomposers to use it up, generally very clear water
• As lakes age, they steadily fill with sediment and become more eutrophic - maybe turning into a bog or marsh and finally land - human activities speed up this natural process, i.e. fertilizer run-off, pollutants

• Oceans cover approximately 75% of the earth's surface and contribute greatly to conditions on the other 25% - i.e., most of the plant's rainfall is provided by evaporation from the ocean, also marine algae produce a large percent of the earth's oxygen and consume large amounts of CO2
• The edges of the sea are the hatcheries and nurseries of many important species, i.e., in the U.S. 1/2 of the commercial harvest of the Pacific and 2/3 of the commercial harvest of the Atlantic and Gulf depend on coastal wetlands and estuaries - these areas are also nesting and feeding areas form many migratory waterfowl - these areas also act as buffers against erosion and flooding further inland
• therefore, ecologists are alarmed at the draining and filling of these areas to build towns and resorts - such destruction of habitat is the most common cause of extinction of wildlife

Classifications of 

Marine Communities

• Light penetration (photic or aphotic)
• Distantce from the shore (intertidal zone, subtidal zone, oceanic zone)

• Area b/w low and high tides 
• This area supports a variety of plants and animals depending on the type of shore (rocky, sandy, muddy)
• Densly populated b/c this area recieves abundant light and minerals washing from the shore

• Area extending from the low tide out to the edge of the continental shelf
• Less temperature fluctuations and less violent wave movement than the intertidal zone
• The subtidal zone is densely populated b/c it also receives abundant light and minerals washing from the shore

Oceanic zone

• The open ocean
• From the edge of 1 continental shelf to another
• Organisms in the open ocean include the plankton (the drifters or floaters), the neckton (the swimmers), and the benthos (the bottom dwellers)

• A group of interbreeding individuals of the same species, living in the same geographic area
• A population has characteristics not found in the individual members

• Gene pool: all the genes of the individuals in the population
• Density: the # of individuals per unit area or volume
• Pattern of distribution: random, clumped, or regular
• Age structure: % of individuals in the 3 ecologically significant age groups (prereproductive, reproductive and postreproductive)

• Houseflies
• Elephants
• English sparrows

2 factors in the growth and

development of populations

• 2 opposing forces
• Biotic potential: ability to reproduce and survive at a given rate
• Environmental resistance: opposition to growth from biological, chemical, and physical forces in nature

• We can use growth curves to understand the interaction b/w biotic potential and environmental resistance
• 2 types: exponential growth (J-shaped) and logistic growth (S-shaped)
• Both types of growth curves are mathematical models - a population will not necessarily fit either one perfectly, however they are useful in predicting how a population will grow under certain conditions

• J-shaped curve
• rate of growth of a population under ideal conditions
• unregulated growth
• cannot continue indefinitely b/c food supplies and space become limited and waste products build up

• S-shaped curve
• Population growth that is slowed by limiting factors
• Growth may start of exponential, but it levels off at the carrying capacity of the environment
• The # of individuals that an environment can support for a prolonged period of time
• Most species typically show this kind of growth curve

Factors affecting

biotic potential

of a population

• An individual's contribution to population growth can be increased in 3 ways
• 1. by producing a larger # of offspring at a time
• 2. by having a longer reproductive live
• 3. by reproducing earlier in life

Reproductive strategies

(life history strategies)

• In each species the # of offspring, frequency of reproduction, and age of 1st reproduction are adapted to the carrying capacity of the environment and result from natural selection
• Generally there are 2 opposing types of reproductive strategies or reproductive responses to growth limits: r-selection and K-selection

• Typically occurs under low population densities in unstable environments and favors characteristics that lead to rapid rates of increase
• r-selected individuals spend a large part of their energy in reproductive efforts
• This would be advantageous in a low-density population b/c it would help increase the population
• Most offspring do not survive but the 1s that do mature rapidly and 5 characteristics of an r-selected population
• 5 characteristic of a K-selected population:
• 1. typically reproduce once
• 2. have many young
• 3. young are small
• 4. young mature rapidly
• 5. young have little or no parental care
• Examples: many insects, weed that invade new habitats (typically have many small seeds)

• Typically occurs in populations at or near the carrying capacity in a stable environment, where individuals spend less energy on reproduction and more energy on competing for available resources
• These are longer-lived individuals that produce a few well-endowed young over their life span
• 5 characteristics of a K-selected population
• 1. typically reproduce more than once
• 2. have few young at a time
• 3. young are larger
• 4. young mature rapidly
• 5. young have little or no parental care
• Examples: many insects, weeds that invade new habitats (typicaly have many small seeds)

r-selection and 

K-selection

• Represent opposite ends of a continuum of reproductive strategies that occur in nature 
• Within a group or within an area, there will be a range of reproductive strategies
• the best choice in the continuum, the choice made by natural selection operating on a population, depends on the properties of the population and the environment

Populations following

r and k-strategies

• Populations following r-strategies would appear to lead riskier lives both as individuals and a species 
• Typically they rapidly exploit an environment and then move on w/ many offspring not surviving
• However, they possess remarkable recovery powers b/c the population can be built up quickly from only a few individuals 
• By contrast, populations following K-strategies would appear to lead safer lives since each individual has a much greater chance of survival, especially when maturity is reached 
• However, these populations may not be able to recover as well when their numbers drop below the carrying capacity

• the length of time an individual of a particular age can expect to survive
• Species w/ different reproductive strategies tend to have different patterns of survivorship
• Survivorship curves: relate these to the differences in parental care
• r-selected type: most individuals die at an early age, many as eggs b4 hatching
• K-selected type: most individuals live for a long time and die as a result of the diseases of old age
• These curves are also mathematical models: meaning that in real populations the survivorship curve may fall somewhere in b/w

Regulation of

population size

• 2 general types of factors limit population growth:
• density dependent
• density independent
• Both of the types of factors, density dependent and independent, are generally at work at the same time in most populations

• As population density increases, these factors intensify and affect a larger proportion (not just a large #) of individuals
• These factors reduce the population growth by decreasing reproduction or by increasing mortality
• Examples:
• Resource limitations - food, space
• Predation - predator more likely to encounter the prey in a crowded population
• Intrinsic factors - high density leads to the stress syndrome in which hormonal and other physiological factors may delay maturation or inhibit reproduction or suppress immunity

• These factors affect the same % of the population w/o regard to its density
• Examples:
• Seasonal weather changes - freezing in winter, heat in summer, etc
• Catastrophic weather events - floods, earthquakes, tornados, forest fires, etc. - a flood, fire, etc. that is severe enough to kill 50% of the population, kills 50% of the population whether it is a large or a small population
• However, bad weather may actually be density dependent in some cases
• If a population can survive by finding shelter and the amount of shelter is limited, then all members of a small population might survive while only a fraction of a larger population will find shelter and survive

• Ultimately responsible for most of our other ecological problems
• The human population has steadily increased for at least the last 10,000 years
• Since the time of the agricultural revolution
• The greatest population growth has been in the last 50 or so years, largely b/c the death rate has been dramatically reduced in most countries b/c of improvements in nutrition and hygience, antibiotics, vaccines 
• It took from the beginning of life until 1950 for the 1st 2.5 billion people to accumulate on earth, but it took just 40 years for the 2nd 2.5 billion to be added
• At the current growth rate, by 2025 an additional 5 billion more people will be added to the current world population of over 6 billion

• The study of populations
• Back in the 1940s, demographers noted that a decline in the death rate in a human population is usually followed within a few generations by a decline in the birth rate
• This decline in the birth rate is the demographic trasition

• The decline in the birth rate which generally follows the decline in the death rate in a human population
• Generally takes from 1 to 3 generations to spread through the population
• It has occurred in most western nations since 1900
• I.e. the avg. # of children born to an American woman declined from 4 in 1920 to 2 in 1980 (and less than 2 today) 
• The single factor most clearly correlated with a lowered birth rate is the increased level of education and employment for women

• Generally takes from 1 to 3 generations to spread through a population
• During its progress, the death rates are lower but birth rates remain high
• The problem is that today some underdeveloped countries are not proceeding through the demographic transition
• They have lowered their death rates (w/ the help of vaccines, antibiotics, and other medical interventions provided by developed countries such as the U.S.), but they have not achieved the social and economic gains needed to reduce their birth rates

• Currently demographic trends have resulted in a demographically divided world
• About 1/2 of the human population is in developed countries that have completed the demographic transition
• These are stable populations (the #s of prereproductives and reproductives are approximately balanced)
• The other 1/2 of the human population is in underdeveloped countries that are stuck in the 2nd stage of the transition where birth rates are still high
• These are expanding populations (the prereproductive outnumber the reproductives)

• When we study the biological forces that affect populations, we are studying community ecology since a community consists of 2 or more populations of different species, living in the same geographic area and interacting w/ 1 another
• Thus, a major theme of community ecology is interactions among organisms - these interactions influence the behavior, distribution, and abundance of organisms

Classifications of Interactions

among organisms

• These interactions are classifies by whether they are beneficial (+) or harmful (-) to each organism: 
• +/+ interactions: both species benefit, i.e. mutualism
• +/- interactions: one species benefits and the other species is harmed, i.e. predation, parasitism
• -/- interactions: both species may be harmed, i.e. competition

• an interaction b/w 2 species in which both species benefit (+/+ interaction)
• There are numerous ex. including: 
• bacteria living in the digestive tract of animals receive food from the animals and in turn help to digest food for the animal - i.e. bacteria in the digestive tract of termites digest the cellulose in wood and bacteria living in the human digestive tract help digest and absorb certain nutrients and also synthesize vitamin K for us
• Lichens consist of an alga and a fungus in a mutualistic relationship in which the alga makes the food by photosynthesis and the fungus attaches to the substrate and absorbs water and minerals
• Mycorrhizae are mutualistic associations of plant roots and fungi, the plant roots provide nutrients for the fungi and the fungi help to absorb water and minerals for the plant
• In seed dispersal, birds or mammals eat a fruit and then deposit the seeds far away from the parent plant
• Shrimp and goby fish live together in a mutualistic relationship in which the fish provides protection and the shrimp shares its burrow with the fish
• Pollinating insects receieve food (pollen or nectar) while spreading pollen from plant to plant, thus ensuring genetic variation by way of cross pollination, some of these associations are very specific such as the yucca plants and yucca moths
• Coral reefs are mutualistic associations of corals and algae in which the corals provide the algae w/ a home and some essential nutrients while the algae provide the corals w/ food produced by photosynthesis

• An interaction b/w species in which 1 species (the predator) exploits another living species (the prey) for food (+/- interaction
• Examples: 
• Hare and lynx: oscillations in growth cycles, also involves a 3rd factor (vegetation - food for the hare)
• Kaibab deer: effects of disruption of predator-prey relationships by human interference

• Not necessarily abundant in a community, but they exert a strong effect on the community structure (not by #s) but by their role in the community
• i.e. the sea star is a keystone predator which preys on mussels (a dominant species and strong competitor) - if the sea stars are removed from the community, the mussels increase in # and they eliminate most other invertebrates and algae - species diversity declines

• Prey populations have some natural defenses against predation such as:
• camouflage
• hiding
• running away
• gathering in large #s
• weaponry
• chemical defenses
• warning coloration

• an interaction b/w species in which the parasite benefits at the expense of the host by living either within the host or on the host (+/- interaction)
• There are numerous ex's, varying in degree of effect, often to the point of near extinction of the host (fungus and the American elm) - if the parasite is too successful (and specific), extinction of the host leads to extinction of the parasite
• On the other hand, there are examples (rabbits and viruses in Australia) in which there is a coevolution of parasite and hot by adaptation and selection that enables parasite-host relationship to exist below the extinction level

• Using 1 organism to control the #s of another 
• Examples: companion planting, beneficial insects

• If the size of a population declines too drastically, the population may become extinct
• Local populations do become extinct often, but are reestablished later by immigration from neighboring populations
• However, when an entire species consists of only 1 small isolated population, it is especially prone to extinction
• Extinction is not a new problem
• About 65 million years ago, more than half of all species on earth, including the dinosaurs, became extinct in a relatively short period of time
• Biologists are still arguing about the cause, but whatever the cause, it was a natural cause

• Today, however, most species extinctions are caused by human activities such as: 
• Destruction of habitat
• Competition from human-imported species
• Overhunting
• Humans caused extinctions are eliminating species much faster than new ones can form
• This destroys an irreplaceable resource
• Coadapted gene pools that might be valuable to agriculture or medicine, also vital links in the food chain are being destroyed

• An interaction b/w populations living in a common environment and sharing a limited resource (-/- interaction)

Gause's Principle of

Competitve Exclusion

• if 2 species are in competition for the same limited resource, 1 species will be more efficient at utilizing that resource and will eventually eliminate the other species in situations where they occur together
• Thus, 2 different species cannot occupy the same niche in the same place for very long

• A place where an organism lives 
• i.e. forest, desert, lake, ocean, etc

• The functional role that an organism plays in the place where it lives
• i.e. producer, consumer, competitor, predator, prey, parasite, host, etc

Competitve Exclusion 

Examples

• Protozoans
• Duckweed 
• Barnacles

• The physical limits of tolerance of the organism

• that portion of the fundamental niche which is actually utilized
• Determined by physical factors and competition

• closely related species can coexist and avoid excessive competition by assuming different niches, each specializing w/in a narrow range of resource gradients
• This is called resource partitioning
• Sharing the same resource in different ways, in different areas, or at different times

• within a single species
• from the concept of the niche, it should be obvious that competition would be expected to be most keen among individuals of the same species, for here the niche requirements are identical
• Many studies on a variety of organisms have shown that overcrowding and excessive competition w/in a species result in build-up of wastes, scarcity of food, interference w/ feeding and mating, reduction in birth rates, etc. 

Avoiding excessive

intraspecific competition

• 1 way to avoid this excessive intraspecific competition is by territoriality
• A phenomenon in which an individual or a group stakes out a claim on a geographic area which it then defends in some manner against invaders
• This is found mainly in birds and mammals

• The slow process whereby 1 community of plants and animals replaces another 
• Typically a very slow process

• Begins when a new previously unoccupied surface (bare rock, sand, bare soil) eventually results in a plant-animal community which will continue to change by further succession
• Thus, primary succession establishes new communities

• Succession begins when plants invade an area
• This invasion usually occurs in 4 stages: 
• migration
• establishment
• aggregation
• competition

• The pioneer plants typically are lichens (a mutualistic association of an alga and a fungus)
• They help to trap organic debris
• They aid in the chemical weathering of rock - acid by-products erode the rock 
• Natural weathering also occurs by wind erosion, water erosion, freezing and thawing
• All help to break up the rock into smaller pieces 
• This is part of the process of soil formation

• 2 processes involved
• weathering of rock 
• decomposition of organic matter (humus)

Typical stages in

primary succession

on bare rock

• Lichens, mosses, ferns, shrubs, pioneer trees
• birches, for example
• Taller more shade - tolerant hardwood trees
• oaks, for example

• The terminal stage to which a plant community develops under a stable climate forest climax of this area - oak, hickory, beech, maple
• Not all regions will go to a forest climax - it depends on climate (temp and rainfall mainly) and geography

• The recovery of a once-vegetated area as it grows again toward climax
• i.e. after a forest fire, volcanic eruption, or clear-cutting
• Thus, secondary succesion replaces disturbed communities

• A community of plants and animals plus their non-living environment through which energy flows and minerals cycle
• Can sustain itself indefinitely if it contains the resources necessary to support its resident organisms and to dispose of their wastes

• Abiotic components
• Biotic components

• water
• oxygen
• carbon dioxide
• minerals
• continuous supply of energy

• producers: the green plants, use energy from sunlight to produce food
• Consumers: various levels, depending on what they eat
• Primary consumers: herbivores, eat the producers
• Secondary consumers: carnivores, eat the primary consumers
• Tertiary consumers: carnivores, eat the secondary consumers
• Decomposers (detritivores): bacteria and fungi, break down organic matter (waste products and dead bodies which are called detritus)
• Omnivores are primary consumers  when they eat things like nuts or fruit. They are secondary consumers when they eat meat.

• An organism that is unable to synthesize its own organic carbon-based compounds from inorganic sources, hence feeds on organic matter produced by, or available in, other organisms
• Consumers: herbivores, carnivores, and omnivores
• All animals, some fungi and most bacteria
• They are not capable of producing their own food, therefore they obtain their energy requirements by feeding on organic matter or another organism

• A series of organisms, each of which is eaten by the next
• However, food chains are rarely isolated sequences
• They are usually interconnected w/ one another in an overall pattern called a food web

• The trophic level to which an organism belongs indicates the feeding level in the food chain
• 1st trophic level: producers
• 2nd trophic level: primary consumers
• 3rd trophic level: secondary consumers
• But will the food web concept, an organism cannot alway be assigned to 1 specific level
• It may be feeding on more than one level

• The flow of energy through an ecosystem can be represented in the form of a pyramid of energy
• It is smaller at the top b/c energy is used and lost at each level
• This limits the # of trophic levels in an ecosystem
• There are seldom more than 4 or 5

• Not all food available at 1 trophic level is actually eaten
• Not all of the food eaten is useful, i.e. growth of consumers is often limited by the content of nutrients such as essential amino acids in their food - in the process of eating enough food to get all of the amino acids they need, they may egest and waste large amounts of food
• Also, the amount of energy at each level that is available to be passed on is reduced b/c the organisms at each level use energy in metabolism to maintain their bodies and lose heat energy from their bodies
• Therefore, b/c of all of these energy losses from 1 trophic level to the next, there is not enough energy left to support higher and higher levels
• This concept can also be illustrated by using a pyramid of biomass or a pyramid of #s

• The amount of organic matter produced by the members of a given trophic level during a given period of time
• Primary productivity
• Secondary productivity

• Rate at which energy is stored in organic matter by photosynthesis in the producers
• Gross primary productivity minus respiration = net primary productivity
• Net primary productivity is the amount that appears as plant growth and is available for consumers
• Primary productivity varies considerably in different ecosystems b/c of different limiting factors such as temp, rainfall, and length of growing season

• Rate of formation of new organic matter by heterotrophs
• On avg, animals convert only about 10% of the energy they consume into new animal growth

• The movement of nutrient elements through an ecosystem by physical and biological processes
• The name indicates that the circulating chemicals are associated with both the living and the non-living parts of the ecosystem

• Sedimentary: major reservoir is some sedimentary material such as soil, rocks, or water
• Atmospheric (gaseous): major reservoir is the atmosphere

• Phosphorus cycle
• Carbon cycle
• Nitrogen cycle
• Water cycle: evaporation, precipitation, runoff

• The Hubbard Brook Experimental Forest in New Hampshire, it has been shown that a forest is extremely efficient at retaining minerals
• 1 experiment examined what happens when a forest is cut down
• Trees and shrubs in a valley were removed, resulting in a dramatic effect almost immediately
• The rate of loss of inorganic nutrients dissolved in stream water increased 6 to 8 times as much as in control area w/ no cutting (these are nutrients that would have been taken up by the trees)

• pH of normal rain is about 5.6 b/c of carbon dioxide and other gases that form acids as they dissolve in rainwater
• Since the mid-1960s however, rain in the easter U.S. has become more acidic w/ pHs averaging 4 to 4.2 and sometime 3.0 or lower
• It has been recorded as low as 1.5 in W. VA

• Acid rain occurs when sulfur oxides and nitrogen oxides in the atmosphere react w/ water in the air to form acids
• These sulfer and nitrogen compounds found in acid rain come mainly from human activities such as industrial pollution, automobile exhaust, burning of fossil fuels and to a much lesser extent from natural causes such as volcanic eruptions and release of sulfur gases from anaerobic bacteria living in wetlands

• Add industrial pollution controls
• Develop and use antipollution devics

• An undesirable change in an ecosystem's physical, chemical, or biological characteristics
• All organisms release waste products into the environment, making the environment less suitable for that organism
• But in a balanced ecosystem, 1 organism's wastes are another organism's food (since the decomposers break down wastes and keep them from accumulating)
• Pollution occurs when wastes (mostly from human activities) are not destroyed as fast as they are produced or cannot be bio-degraded by the decomposers
• Instead they accumulate, making the environment less hospitable to human and other life