-an association of interacting populations, usually defined by the nature of their interaction of the place in which they live

-a community is spacially defined and includes all the populations within its boundaries

-communities are often named after their most conspicuous members (ie. riparian forest community)

holistic/individualistic concepts

-holistic-

-the view that a community is a superorganism whose functioning and organization can be appreciated only when it is considered as an entire entiy

-one can understand each species only in terms of its contibution to the dynamics of the whole system

-community is more than sum of its individual part

-individualistic-

-the view that community structure and functioning simply express the interactions of individual species that make up local associations, and do not reflect any organization, purposeful or otherwise, above the species level

-because natureal selection acts on the reproductive output of individuals, each population in a community evolves so as to maximize the reproductive success of its own members, not to benefit the community as a whole

-middle point-

-most species interactions areantagonistic and that communities may be assembled haphazardly, but also admits to the holistic premise that some attributes of community structure and function arise only from interactions among species.

-Community structure is difficult to define and measure

-one of the simplest and most revealing measures of a community's structure is the number of species it includes (species richness)

-about 1.5 million species have been names worldwide, while estimates range up to there being tens of millions

-to manage complexity of comunities, ecologists often partition diversity into numbers of species at each trophic level: primary producers, herbivores, and carnivores

-within trophic levels, method or location of foraging distinguishes different guilds of species: herbivores for example, include leaf eaters, stem borers, root chewers, nectar sippers, and bud nippers

CLOSED

-from a holistic viewpoint, the species belonging to a community are closely associated with one another, which implies that the ecological limits of distribution of each species will conincide with the distribution of the community as a whole

 -F.E. Clements

-Holistic Organization

-Distinct Boundaries(ecotones)

-Coincident Species Ranges

-Prominent Coevolution

OPEN

-from an individualistic viewpoint, each species is distributed independently of others that coexist with it in a particular association

-has no natural boundaries; therefore, ecological distributions of its member species, which may extend their ranges independently into other associations

-H.A. Gleason

-Individualistic Organization

-Diffuse Boundaries

-Independent Species Ranges

-Uncommon Coevolution

-closed communities are discrete ecological units with distinct boundaries, called ecotones.. these are regions of rapid replacement of species along an environmental gradient

-we can observe these when 1)the physical environment changes abruptly and 2)when one species or life form dominates the environment that the edge of its rangedetermines the distribution limits of many other species.

*can have partial ecotones, ie. the separation b/w serpentine and non-serpentine soils. Some species live only on one side of the ecotone, some live all across, and others live only within the ecotone

-ecotones are less likely to occur over gradients of gradual evironmental change

-continuum concept refers to the concept of open community organization

-within broadly defined havitats, such as forest, grassland, or estuary, populations of plants and animals replace one another continuously along gradients of physical conditions

-each of the different species that co-occurs at a single locality in Kentucky has a different geographical distribution

-Montane plant distributions indicate open commmunity structure (from wet to dry) (as one increases, another decreases)... while in arizone there is a hint of ecotones

gradient analysis

-the validity of the continuum concept depends on the way in which species are distributed along ecological gradients

-in a gradient analysis, closed community organization should reveal itself by the preence of sharp ecotones.

-feeding relationships organize communities in food webs

-when we apply a food web perspective to the community, we tend to emphasize diversity

-although food webs are also based on functional relationships, they stress connections b/w populations and recognize, for example, that not all herbivores consume all producers

-food web analysis has greater power than ecosystem analysis to differentiate community structure (looks at species level)

-as communities become more diverse,species exert greater influence on one another through their various interactions

-predators influence the diversity of lower trophic levels

-study by Robert T Paine compared Pisaster to Heliaster

-showed that consumers could promote diversity and thereby control the structure of a community

-these are keystone predators because when they are removed, the edifice of the community tumbles

-described by Paine

CONNECTEDNESS WEBS

-emphasize feeding relationships among organisms, portrayed as links in a food web

ENERGY FLOW

-represent an ecosystem viewpoint, in which connections between species are quantified by flux of energy between a resource and its consumer

FUNCTIONAL WEBS

-the importance of each population in maintaining the integrity of a community is reflected in its influence on the growth rates of other populations

-can only be revealed by experiments

omnivory- feeding on more than one trophic level

-different communities of similar diversity may have different food web structures

trophic levels are influenced fro above by predation and below by production

-trophic cascade is the influence of consumers or producers on poulations that are two or more trophic levels removed

-when higher trophic levels determine the size of the trophic levels below them, the situation is referred to as top-down control

-bottom-up control is the opposide

-a survey of zooplankton and phytoplankton densities in natural lakes (Mathew Leibold) showed that the primary consumer trophic level varied in parallel with the producer trophic level, a pattern that is consistent with bottom-up control.

-however, when predatory fish were added to the experimental lakes to decrease the density of zooplankton, phytoplankton abundance increased in most cases, sometimes by a factor of more than 10, indicating top-down control

-trophic cascade experiments (inorganic nutrients to experimental microcosm comunities..... bottom-up)

-results revealed that both bottom-up and top=down control of trophic level size

-increased primary production tends to augment all the overlying trophic levels, however, the experiment also showeed that consumers could depress the size of the trophic level immediately below them and increase the abundance of organisms two levels below.

***bottom up increases everything**
**top down makes fluctuations***

-Christen Raunkiaer noted early in the twentieth century that within a particular community, a few species attain high abundance, and they are the dominants in the community, whereas most others are represented by relatively few individuals.

-when he plotted the number of individuals of several different species on the same trophic level, the result was a reverse J shaped curve

-abundances of species can also be plotted ona logarithmic scale

-

-more species occur within large areas that within small areas

-Olaf Arrhenius first formalized this species-area relationship

S=cA^z

(c and z are constants)

-z usually 0.2-0.35 (ie. # species increases in proportion to 1/5-1/3 power of area

-**z is usually lower in continental areas than islands

 *area and habitat diversity both contribute to the species-area relationship

-weight species richness by relative abundance

-as more individuals are sampled, probability of encountering rare species increases

-also, not all species should contribute equally to our estimate of total diversity because their functional roles in a community vary in proportion to their overall abundance

-in diversity indices, the contribution of each epecies is eighted by its  relative abundance (ie. the proportion of the total number of individuals in a community that belong to that species)

-two indices used widely in biology are

-Simpson's index

-Shannon-Wiener index

-both are calculated from the proportion of each species in the total sample of individuals

D = 1/ Σp_i²

-D = simpson's index.. ranges from 1-S, depending on variation in species abundances

-pi is the proportion of each species

-for example, when 5 species have equal abundances, the value of D is 5

-thus, the diversity index of this sample is 5, which is the number of species in the sample

-when five species have uneqal abundances, the diversity index is less than the total number of species

H = -Σp_ilog_ep_i

-higher H means greater diversity

another problem in esstimating species diversity is that the number of species in a sample  tends to increase with the number of individuals sampled. If we wish to standardize measurements of diversity for comparison, we must base them on comparable sample sizes. When samples include different numbers of individuals, comparability can be achieved by a statistical procedure known as rarefaction, in which equal sized subsamples of individuals are drawn at random from the total sample

-rarefaction can be thought of as a means of portraying the relationship between number of species and sample size

-Howard Sanders applied this technique to samples of benthic marine organisms dredged from soft sediments at various localities in several marine environments

*for samples of comparable size, diversity varies among different habitats

-when a habitat is disturbed (a forest cleared, a prairie burned, a coral reef obliterated by a hurricane, etc) the community slowly rebuilds

-the sequence of changes initiated by disturbance is called succession, and the ultimate association of species achieved is called a  climax community

-plants dispersed by physical forces are the first to arrive in primary succession (sea/wind/animal.... mostly sea dispersed in the beginning, then wind.... once things start to grow, then animal dispersed as well (animals havea reason to come)

-a series of stages of community change in a particular area leading towards a stable state

-beginning with Clement's classic work on succession, ecologists have classified seres into two types according to origin

primary succession -is the establishment and development of plant communities in newly formed habitats previously lacking plants..... sand dunes, lava flows, rock bared by erosion, etc.

secondary succession - is the regeneration of a climax community following a disturbance

-distinction is blurry b/w the two, as in the case of a largescale disturbance

-some ponds undergo bog succession (fills with organic detritus)

-primary succession best studied through receding glaciers

-investigated the colonization of artificially created bare patches by various subtidal invertebrates that grow on hard surfaces

-attemped to ask "How does gap size influence succession on marine hard substrates?"

-found that small R-selected organisms developped quickly as they were adapted to succession, but were eventually replaced by longer living and more resiliant species.

-colonizing ability and competitive ability were found to be inverse

-climax community is the endpoint of succession

-the many seres found within a region often progress towards the same climax

-continuum index -a scale of an environmental gradient based on changes in physical characteristics or community composition laong that gradient

ie. Curtis and MxIntosh used this for Wisconsin forest types

-embodies Clements's view of succession as a developmental sequence in which each stage paves the way for the next, just as structure follos structures as an organism develops

-colonizers allow others to invade

-also occurs in marine systems (seeds of surfgrass have barbs that enable them to become attached to certain types of early successional algae

-inhibition of one species by the presence of another is a common phenomenon, which we have discussed in detail with respect to competition and predation

-sometimes colonization depends on precedence... who gets there first (ie. adults inhibit other species of colonizers)

-through this mechanism,  a species can invade new habitat and become established independently of the presence or absence of other species, depending only upon its dispersal abilities and the physical conditions of the environment

-competitive exclusion then shapes the ensuing sere

seed banks -early seral species produce many small seeds that are usually wind dispersed ... their seeds can remain dormant in the soils of forest and shrub habitats for years, until fires of treefalls create the baresoil conditions required for their germination and growth

-the seeds of most climax species are relatively large, as competition is high

**the survival of seedlings in shade is directly related to seed weight

EARLY

-many small seeds

-wind/animal dispersal

-long seed viability

-low root:shoot ratio

-rapid growth

-small mature size

-low shade tolerance

LATE

-few, large seeds with limited viability

-dispersal by gravity/eaten by animals

-high root:shoot ratio

-slow growth/large mature size

-high shade tolerance

-not all climaxes persist

-ie. seasonal ponds.. each year restocked

-scavengers may also form a pattern oftransient succession (no climax... even though succession of dead animal use)... though scavengers may be part of a larger savana climax

-in simple communitites, these can be created by the particular life history characteristics of a few dominant species

-species A causes B which causes C which causes A

Scotland:

-extensive wind damage, and shredded foliage and broken twigs create openings for further damage, and the process becomes self accelerating

-regeneration occurs on protected side of damaged area

-migratory in direction of the wind

-habitats with simple vegetation structure, such as grasslands and marshes, have fewer species than more complex habitats with similar primary productivity.

MacArthur plotted the diversity of birds observed in different habitats according to diversity in foliage height

-bird species diversity is correlated with foliage height diversity

-the level of potential evapotranspiration has been found to be a good predictor of diversity over large regions

-it is the amount of waer that cold be evaporated from the soil and transpired by plants

-the correlation b/w PET and diversity has become known as the energy-diversity hypothesis

-local (beta) diversity is the number of species in a small area of homogeneous habitat. Clearly it is sensitive to how one defines habitat and the intensity of sampling in community

-regional (gamma diversity) - is the total number of species observed in all habitats within a geographic area that includes no significant barriers to dispersal of organisms

-how we define a region depends on which organisms we are considerign

*if each species occurred in all habitats within a region, local and regional diversities would be the same.

beta diversity - the difference, or turnover, in species from one habitat to another within a region

regional diversity = local diversity X beta diveristy

-the species that occur within a region are referred to as its species pool

-these are the potential members of a community

-the presence of a particular species within a local community signifies thatthe species can tolerate the conditions of the environment and find suitable resources for survival and reproduction. we say that these conditions occur within the fundamental niche of the species (the range of conditions and resources within which individuals of the species can persist)

-other species may restrict the distribution of a particular species to those parts of its fundamental niche where it is most successful. This more restricted range of conditions and resources is referred to as the realized niche

-

species sorting - restriction of species from a regional pool in local communities owing to their tolerance of conditions, requirements for resources, or interactions with competitors/preditors.

-Weiher and Keddy's experiment shows how after time, certain species are eliminated and a few dominate (wetland plants)

-these depended on certain environmental conditions (ie. water height)

-some species always present, some occasionally present

-expansion of habitat and resource use by populations in regions of low species diversity resulting from low interspecific competition

-can be seen in surveys of bird communities

-show that where fewer species occur, each is likely to be more abundant and to live in more habitats (closer to fundamental niche)

*as the diversity of the region increases, habitat breadth and local abundance of individual species decrease

-while local diversity and turnover of species b/w habitats increase(ie. beta diversity)

-total community niche space

-extent of niche overlap

-the niche breadth of individual species

1)increased resource diversity

2)increased niche overlap (increased sharing, productivity of each species would decrease)

3)increased specialization (average productivity would also decline here)

---a combination of these things occur in the tropics

-species added to a community increase the variety of ecological roles played by its members

-niche relationships can be portrayed in morphological space (ie. bats)

-distribution in morphological space differs b/w the aerial-feeding bat faunas of Ontario and Cameroon, West Africa

-in less diverse Ontario, all the bat species have similar morphology and all play similar ecological roles (insectivores)

-the bats of the morphologically diverse community in Cameroon play a greater variety of ecological roles (insects, fruit, nectar, fish, bat eaters)

-also, diversity is smallest in headwater springs of rivers, and the greatest diversity occurs at the end of the river (diets, and thus morphology become more complex)

-higher productivity results in more energy reaching higher trophic levels and therefore supporting larger populations of predators

-increased predation pressure should reduce competition among prey species and permit more prey to coexist

-avenues of escape from predators represent ways in which species may diversify

 -the variety of color patterns and resting positions exhibited by moths, which reflect the variety of backgrounds against which they hide during the day to avoid visually hunting predators, tends to by much higher in more diverse tropical communities than it is in temperate moth communities

-equilibrium theories of diversity balance factors that add and remove species

-equilibrium theory of community diversity resembles the theory of density-dependent regulation of population size

MacArthur

equilibrium theory of island biogeography - states that tthe number of species on an island balances regional processes governing immigration against local processes governing extinction

-flora and fauna of the closest continental areas make up the species pool of potential colonists

-as the number of species on the island increases, the rate of immigration of new species to the island decreases

-where immigration and extinction curves cross, the corresponding number of species on the island attains a steady state at the level Š

-smaller islands support fewer species becuase of higher extinction rates

-islands close to the mainland support more species because of higher immigration rates

Simberloff/Wilson did experimental manipulations of island faunas

-found that  the re-colonization of four small islands supports the equilibrium theory of island biogeography

-major difference b/w islands and continental regions is that in continental regions, new species are more likely to form within the region, as well as arriving from outside the region by immigration

*evolution + immigration = speciation

1)environmental heterogeneity allows species to coexist because they can specialize on different parts of the niche space

2)Gaps creasted by disturbances provide environmental conditions to which species may be specialized

3)Herbivores and pathogens affect common species more than they do rare ones, and the resulting rare species advantage allows diversity

4)because species of trees are similar ecologically, competitive exclusion takes a long time, and the species added to a community are likely to remian

-argument that diversity of trees varies in proportion tot he heterogeneity of the environment

-soil and climatic conditions

-not enough of an explanation....

-Connell relates the high diversity of tropical rain forests to habitat heterogeneity created by disturbance

-for this intermediate disturbance hypothesis to account satisfactorily for differences in diversity b/w regions,there would have to be comparable differences in the level of disturbance

-rains are heavier, soils have less organic matter, and the sun is directly overhead... creates more heterogeneity b/w forest gaps and rest of environment

=Steve Hubbell investigated the recruitment of tree seedlings in gaps in a tropical rain forest. said that the number of species was the same in gaps and in non gap control sites

-led him to suggest that even though species of trees may be specialized differently for germination sites, the species that actually invade a particular gap depend more on the vagaries of recruitment than on the particular ecological conditions in the gap\

***the death rate of canopy trees does not differe b/w tropical and temperate forests.

-explains why monocultures fail

-the hypothesis states that seedlings should be less likely to establish themselves close to adults of the same species than at a distance

* seedlings are most dense close to the parent tree, but survival of seedlings is highest at a distance, where seedlings escape the detrimental effects of crowding close to the parents**

-pest pressure and recruitment limitation can reduce the consequences of interspecific competition for community members

-Hubbell has argues that these factors make most species of tropical trees competitively equibalent.

-consequently, new invaders are likely to remain for long periods.

-characteristics shared by a lineage irrespective of environmental factors

-these effects reflect the inertia of evolution... the lack of change of some attributes in the face of change in the environment

-earth formed 4.5 bya

-atmosphere had very little oxygen... most of history of the earth, life forms were very primitive

-eventually photosynthesis produced enough oxygen in the atmosphere for oxidative metabolism

-eukaryotic cell within last 1 billion years

-around 590mya, most of modern phyla of invertebrate organisms appear in the fossil record

-animals began to protect themselves with hard shells

3 eras of life: paleozoic, mesozoic(age of reptiles), cenozoic(most recent)(age of mammals)

-camprian is first period within paleozoic (hard shelled animals)

-then ordovician

-the movement of landmasses on the surface of the earth

-position of landmasses influences climatic conditions

-drift creates and breaks down barriers to dispersal, alternately connecting and separating evolving biotas in different regions of the earth

Pangea-about 200 mya in the early mesozoic era ... was a giant single continental landmass

By 144 mya, att he beginning of the cretaceous, the northern continents (Laurasia) had separated from the south (Gondwana) , with the Tethys Seaforming in the space between them

-by the end of the mesozoic, 65mya, South America and Africa were widely separated

-connection between Australia and South America through a temperate Antarctica finally dissolved about 50mya

-Europe and Africa joined about 17 mya, and N/S America joined around 5 mya.

-the splitting of a widely distributed ancestral population by continental drift

-lineages of ratite birds were separated by the fragmentation of Gondwana (rhea, ostrich, emu, kiwi, etc)

-developed by Alfred Wallace

Nearctic/Palearctic regions, corresponding roughly to North America and Eurasia, maintained connections across either what is now Greenland or the Bering Strait between Alaska and Siberia throughout most of the past 100 million years

-the continents of the Southern Hemisphere, particularly Africa (Ethiopican region) and Australia (Australian region), experiences long histories ofisolation from therest of the terrestrial world, during which time many distinctive forms of life evolved in each

-the oriental region includes the biota of SE Asia, which was isolated from tropical areas of Africa and South America in addition to contibutions from the landmass of India.

-stronger relations exist between palearctic/oriental than between nearctic/neotropical (SA)

-when they connected, more North American groups entered South America than the reverse

-large South America extinction epidemic was the result

-alternating periods of coolingand warming led to the advance and retreat of ice sheets at high latitudes over much of the Northern Hemisphere  and caused cycles of cool, dry and warm, wet climates in the Tropics over last 2 million years

-around 18k years ago, a general pattern of reforestation occurred in NA

-migration of many types of trees in NA from pleistocene refuges 18k years ago to their present distributions can be seen and studied

-most famous was 65 mya

-evidence points to the shallow seas off of Mexio

-evidence of the explosion appear as a layer of clay in geologica strata all over the world

-asteroid 10km in diameter and traveling 25km per second

-Organisms in similar environments converge in form and function

-convergence is the process whereby unrelated species living under similar ecological conditions come to resemble one another more than their ancestors did

-several unrelated birds have becoe convergently adapted to extract insects from wood

-unrelated African and South American rain forst mammals show striking convergence

-regional processes and the unique histories of different regions have left an imprint on local community diversity

-understand 24.13

-saturation of local communities can be tested by relating local to regional diversity

-when local diversity increases in proportion to regional diversity, no limit to species coexistence is indicated

-when local diversity levels off at higher regional diversity, interactions within communities limit the number of coexisting species.

*the number of fish species in short stretches of river (local) is directly proportional to the regional pool of species within entire river drainages in both northern SA and West Africa

-species pool for temperate North America is 253, 124 i nEurope, and 729 in temperate east asia.

-regional and local diversity appear to be closely related

-larger corridor in asia

-also result of higher rate of species production over Tertiary period

-are tropical forests that occur within tidal zones along coastlines and river deltas

-tolerate high salt concentratios and anaerobic conditions

-presetly, mangrove flora ofthe Atlantic and Caribbean includes 7 species, while in the Indo-West Pacific includes at least 40 species

-not due to habitat availability

-diversity appears to have resulted from plant taxa invading mangrove habitats more frequently in the Indo-West Pacific than in the Caribean region, although the reasons for this are not clear

-in addition, fewer lineages may havesuffered extinction in the IWP

-in latter part ofTertiary, terrestrial habitats fringing Caribbean were arid 

Processes on many scales influence biodiversity

-24.19 is really good

-several processes ar important to the regulation of biodiversity, each with a different characteristic scale of time and space

-scale in time varies from behavior, through demography and population regulation, and then competitive exclusion, and evolution

-scale in space varies from the activity ranges of individuals, through the geographic and ecological dispersal of individuals within populations , to the expansion and contraction of geographic ranges of populations.

-local diversity depends on local rates of extinction, (predators/disease/exclusion/physical environment/etc) and regional rates of immigration

1)reduce human population

2)reduce amount of consumption

3)maintain ecosystems

-biodiversity includes the many unique attributes of all living things... an evolutionary term

-ecological diversity refers to adaptations that define an animal's place in nature

-species whose distributions are limited to small areas are called endemic species, and regions with large numbers of endemic species are said to possess a high level of endemism

-conservation of global biodiversity is best served by directing efforts towards areas of high endemism/high diversity

-oceanic islands are well known for harboring endemic forms; ie. Galapagos/hawaii

-Norman Myers identified 25 biodiversity hotspots worldwide, which they have proposed for special conservation consideration

-these areas occypy 1.4% of total land area of the earth, yet hold as many as 44% of plant species and 35% of terrestrial vertebrate species.

-within these areas, an average of 88% of natural vegetation has already disappeared

-estimates that 1 species disappears each day on earth

MORAL RESPONSABILITY

-rights of non-human lives are as important as human lives

ECONOMIC BELIEFS

-1/4 of prescriptions filled in USA are extracted from flowering plants

-ecotourism confers economic value on biodiversity

INDICATION OF ENVIRONMENTAL QUALITY

-predatory birds were important bioindicators of the effects of the pesticide DDT

-manufacture and export still legal in USA

MAINTENANCE OF ECOSYSTEM FUNCTION

-diverse systems are better able to maintain high productivity in the face ofenvironmental variation

-Tilman and Downing demonstrated that biomass production was less affected by severe drought on high diversity plots than on low diversity plots

-such results can be explained by positing that higher diversity systems are more likely to include some species that can withstand particular stresses. As the environments changes, different species can take over the roles of predominant producers in a system

 -also, experiments show that increasing the number of guilds among primary producers or increasing the number of links in the food web increases ecosystem productivity and stability in the face of environmental variation

background extinction - as ecosystems change, some species disappear and others take their places. This is the turnover of species, at a relatively low rate

mass extinction - refers to the dying off of large numbers of species due to catastrophe

anthropogenic extinction- extinction caused by humans

-the lifespan of a species generally falls within the range of 1-10 million years

-background extinction rate is estimated to be around 1 species per year

-T.C. Foin recently surveyed the causes of population declines for endangered species in the USA

-the primary causes they found were 1)habitat fragmentation (67%) 2)small population size 3)introduction of exotic species, and 4) overexploitation

FRAGMENTATION/REDUCTION

-drastic changes in climate during the ice age combined with dispersal barriers such as the Mediterranean Sea are responsible for today's impoverished European fauna/flora

INTRODUCTION OF EXOTIC SPECIES

-Hawaii's native tree snails are being eliminated b¥ introduced predatory snails 

-tons of examples.... get one and don't know? prob introduction of exotic sp...

OVEREXPLOITATION

-weapons and other harvesting tools

-often changes species composition in a community

-whereas cod were abundant in catches on Georges Bank until early 60s, they have since been largely replaced by skates and dogfish sharks

-the overexploitation of some food species has forced people to switch to others

-Remains offood items in Paleolithic achaeological sites in Israel and Italy document a shift from easily caught prey (tortoises/shellfish) to prey requiring more hunting skill.

VULNERABILITY TO EXTINCTION IS POORLY UNDERSTOOD!

-since species tend to exist for so long, the forces that cause a population to embark on a decline to extinction may be very subtle

-conservation plans for individual species must include adequate habitat for a self-sustaining population

**the design of nature preserves must take into account the ecological requirements of the species and the amount of space needed to support minimum viable population (the smallest population that can sustain itself in the face of environmental variation)

-must be large enough to avoid stochastic processes, and also be distributed widely enough so that to avoid local calamities

-

-The Greater Yellowstone ecosystem is one of the few places where buffalo have access to large areas of grazing land

-populations that undergo long-distance and seasonal migrations present conservation challenges (sandpipers and turnstones feed on eggs laid by horseshoe crabs.... the habitat is necessary for migrating birds)

-conflicting interests and values present obstacles to conservation

-In Washington and Oregon, the fate of the spotted owl has come into conflict with the timber industry

-there are 3 guiding principles:

1)species-area relationship

2)avoidance of edge effects

3)freedom to migrate

 -one large area is better than several smaller areas

-corridors connecting isolated areas are desirable

-circulare areas are better than elongate ones with lots ofedge

-of terrestrial production, 35-40% is used by humans, either directly as food and fiber crops or indirectly as feed for animals

-75million tons of fish

Pauly and Christensen assume that for each step in the chaing of feeding relationships, about 90% of consumed energy is used to maintain the consumer

-ie only 10% is converted through growth and reproduction to biomass

-Lotka was teh first to consider populations and communities as energy-transforming systems

-he believed that the size of a system and the rates of energy and material transformations within it obeyed thermodynamic principles

-energy transformations of ecosystems grow in direct proportion to their size (ie. total mass of constituent organisms), productivity rate, and inefficiency

Raymond Lindeman adopted Tansley's ntion of the ecosystem as the fundamental unit in ecology and Elton's concept of the food web, including inorganic nutrients

-food chains- the sequence of feeding relationships by which energy passes through the ecosystem

-trophic levels - links in a food chain... plant, herbivore, etc

pyramid of energy-less energy reaches each higher trophic level

ecosystem ecology-the cycling of matter and the associated passage of energy through an ecosystem provides a basis for characterizing that system's structure and function

E.P Odum wrote Fundamentals of Ecology was a huge influence in ecosystem ecology

-he depictedecosystems as energy flow diagrams

-for any one trophic level, a diagram features a box representing the biomass of all the organisms making up that trophic level at any given time

-superimposed on the box are pathways representing the flow of energy through that trophic level

****the net production of one trophic level becomes the ingested energy of the next higher level

***Odum extended his model to include the cycling of nutrients, which are retained in the system

-

-plants, algae, and some bacteria capture light enegy and transform it into the energy of chemical bonds in carbohydrates... quantified as primary productivity

-6CO₂ + 6H₂O > C₆H₁₂O₆ + 6O₂

-photosynthesis transforms carbon from a low energy oxidized state to a high energy reduced state in carbs

-plants and other photosynthetic autotrophs form the base of all food chains, and are thus called primary producers

****the difference b/w gross and net primary production is the energy of respiration, which is the amount used by plants for maintenance and biosynthesis

IN

-CO2 uptake measured by decrease in closed chamber or by uptake of carbon-14 labeled CO2

-water and minerals are difficult to measure and not directly related to rate of photosynthesis

OUT

-in aquatic ecosystems, change in concentrations measured in closed chamgers... light and dark bottle method

-water not directly related to rate of photosynthesis

-CARBS-harvest methods can be used to measure NPP

Mwasurements of CO2 flux in dark and light can provide an estimate of gross primary production

-Net uptake in light(NPP) + production in dark(resp) = gross uptake (GPP)

-primary production is sensitive to variations in light and temperature

-photosynthetic efficiency is the percentage of the energy in sunlight that is converted to NPP during the growing season

-where water and nutrients do not limit plant production, this efficiency is between 1-2% in the ecosystem

-water limits primary production in many terrestrial habitats

-when stomates close to prevent water loss, CO2 cannot be taken up, and photosynthesis slow to a standstill

-transpiration efficiency is the drought resistance of a crop, which is also called water use efficiency

-(g dry matter produced per kg water transpired)

-swamps and marsh, tropical forest, temperate forst, estuaries, and algal beds and reefs have highest NPP

-tundra, open ocean, desert scrub have lowest

Ingested Energy - Egested Energy = Assimilation Energy

Assimilated Energy - Respiration - Excretion = production (10%)

-the overall ecological efficiency of th food chain begins with the efficiency with which organisms assimilate the food they consume

-this is the ratio of assimilation to ingestion, usualy expressed as a percentage

**food of animal origin is more easily digested than food of plant origin (predators assimilate 60-90%, herbivores 30-70)

-The most active animals have the lowest net production efficiencies

the ratio of energy contained in production to total assimilated energy is referred to as net production efficiency

-active, warm blooded animals exhibit low efficiencies, those of birds are less than 1%

-these oganisms use most of their assimilated energy to maintain salt balance, circulate blood, produce heat for themselves, and move

-cold blooded animals can channel as much as 75% towards growth and reproduction

gross production efficiency is the product of assimilation efficiency and the net production efficiency

GPE = (assmilation/ingestion) X (production/assimilation) X100

or

= (production/ingestion) X 100

-is usually b/w 1-30%

** in plants, which don't ingest/assimilate fod, efficiency is defined as the ratio of net production to gross production.

-most of the production of terrestrial plants is consumed as detritus... dead remains of plants and undigestible excreta of herbivores- by organisms specialized to attack wood, leaf litter, and fibrous plant egesta

-energy of detritus tends to move into the food chain much more slowly than the energy assimilated by herbivores

-little energy accumulates in any one trophic level

-rather, a balance is achieved b/w the production of biomass at one level and its consumption at another... so that trophic structure of an ecosystem remains constant

-exploitation efficiency is the proportion of production on one trophic level that is consumed by organisms on the next higher level.... less than 100%

ecological efficiency = (exploitation efficiency)X(gross production efficiency)

-the rate of transfer of energy between trophic levels is the residence time in each trophic level, and it provides a second index to the energy dynamics of an ecosystem

-the longer the residence time, the greater the accumulation of energy

-the average residence time of energy at a particular trophic level equals the energy stored divided by the rate at which energy is converted into biomass

-we may also calculate the residence time defined by this equation in terms of mass rather than energy, in which case it expresses the biomass accumulation ratio

 =biomass/rate of biomass production

-the residence time of energy in accumulated litter can be determined by an equation analogous to that for the biomass accumulation ratio:

 residence time= litter accumulation/rate of litter fall

-biomass accumulation highest in temperate forests/boral and tropical forests... but not swamp and marsh

-cultivated land is the least

-in water, algal beds and reefs have the highest, along with estuaries, and open ocean is least

-ecosystem energetics summarizes the movement of energy throug hthe ecosystem

Lindeman constructed the first energy budget for an entire biological community... Cedar Bog Lake

-the overall energy budget of an ecosystem reflects a balance between income and expenditure

organic materials produced outside the system are referred to as allochthonous inputs. Photosynthesis that ocurs within the system is referred to as autochthonous production

-example of allochthonous inputs is trees hanging over a small stream.

***

Kozlovski concluded that  

1)asimilation efficiency increases at higher trophic levels

2)net and gross production efficiencies ecrease at higher trophic levels

3)ecological efficiencies average around 10%

assimilatory processes are transformations that incorporate inorganic forms of elements into the molecules of plants, animals, and microbes

ie. photosynthesis

-in the overall cycling of carbon, photosynthesis is balanced by respiration, a complementary dissimilatory process that involves the transformation of organic carbon back to an inorganic form.. accompanied by the release of energy.

*most biological energy transformations are associated with teh biochemical oxidation and reduction of carbon, oxygen, nitrogen, and sulfur.

-ie. oxidation of carbon in glucose with releases energy, and the reduction of nitrate nitrogen to amino nitrogen, which forms the building blocks of proteins, which requires energy.

**energy flows through biochemical pathways

-as energy glows through an ecosystem, elements alternate b/w assimilatory and dissimilatory transformations, thus going through cycles

-ecosystems can be odeled as a series of linked compartments

-compartment models of ecosystems can be organized hierarchicaly, having subcompartments with compartments

ie. a compartment that represents available organic forms of nutrients is further subdivided into compartments occupied by autotrophs, animals, and microbes

-evaporation, transpiration, and precipitation drive most movement of water through terrestrial ecosystems

-light energy absorbed performs the work of evaporation

-from a thermodynamic standpoint, evaporation/condensation resemble photosynthesis/respiration

-about 1.4 billion km³ water in biosphere

-more than 97% in oceans

-overland, precip exceeds evap, and evap exceeds precip over oceans

'

-evaporation determines how fast water  moves through the bioshpere

-uses about 1/4 of the total radiation hitting the earth from the sun

-condensation rereleases this energy

-the residence time on the surface (2800years) is about 100K times longer than its residence time in the atmosphere

-energy from sun provides driving force

3 processes:

1)assimilatory and dissimilatory reactions of carbon, primarily in photosynthesis and respiration

2)exchange of carbon dioxide b/w atmosphere and oceans

-oceans contain 50X more CO2 than atmosphere

-residence of C in atmosphere is 5 years

3)sedimentation of carbonates

-occurs only in aquatic systems

-particularly limestone and dolomite

CO2 + H2O > H2CO3

(carbon dioxide dissolves in water to form carbonic acid, which readily dissociates)

H₂CO₃ > H⁺ + HCO₃^- > 2H⁺ + CO₃^2-

 -Finally, when calcium is present, it equilibrates with the carbonate ions to form calcium carbonate

-calcium carbonate has low solubility and sedimentates

-naturally acidic rivers tend to dissolve these and equilibrate the process

**when photosynthesis exceeds respiration (algal blooms), calcium tends to precipitate out of the system

CHANGES IN CARBON CYCLE OVER TIME

-CO2 in atmosphere has decreased since the beginning of the paleozoic era (550-400mya)

-15-20x more than today in atmosphere

-rose to 5X again in mesozoic

*At the start of the Devonian, soil clay content increased, rooting depth and the sizes of other plant parts increased as forests flourised whose carbon was sequestered in coal and carbonate deposits... and atmospheric CO2 concentrations fell.

-The ultimate source of nitrogenfor life is molecular nitrogen (N2) in the atmosphere

-dissolves a little into water, but is absent from rock

-lightning converts some, but mostly caused by nitrogen fixation(assimilation by certain microorganisms)

-more complicated than CO2, as more oxidized/reduced forms are possible

AMMONIAFICATION

-plants obtain nitrogen from the soil, either as ammonia or nitrate, which they then must reduce to an organic form

ammoniafication - involves the breaking down of proteins into their component amino acids by hydrolysis and the oxidation of the carbon in those amino acids... this results in the production of ammonia (NH3)

**ammoniafication is carried out by all organisms

**N is not oxidized in this process, only carbon, so its energy potential does not change

NITRIFICATION

-nitrification - involves the oxidation of nitrogen, first from ammonia to nitrite (NO2-), then from nitrite to nitrate (NO3-), during which nitrogen atoms are stripped of six, and then two more of their electrons

-this releases much of the potential chemical energy of organic nitrogen

-each step is carried out by a specific bacterium

NH₃ > NO₂^- > NO₃^-

-can only occur in the presence of oxygen to act as electron acceptor

NO₃^- > NO₂^- > NO

-this is called denitrification, and is also accomplished by bacteria

-additional reactions can produce molecular nitrogen:

NO > N2O > N2

-denitrification may be a major cause of low availability of nitrogen in marine systems

-when nitrate is used as an oxidizer by bacteria, it is converted into unusuable forms (NO N2)

NITROGEN FIXATION

-nitrogenase is the enzyme responsible for this process in microorganisms, and it is inactivated by oxygen and works efficiently only under extremely low oxygen levels

-live within anoxic root nodules

-reduce N2 to NH3 by oxidizing sugars or other organic compounds for energy

-must get these resources somewhere... symbiosis for Rhizobium

*on a global scale, nitrgen fixation approximately balances the production of N2 by denitrification

-is a major constituent of necleic acids, cell membranes, energy transfer systems, bones, and teeth

-is relatively simple

-it does not undergo oxidation/reduction reactions in its cycling through the ecosystem

-plants assimilate phosphorus as phosphate directly from soil or water and incorporate it directly into various organic compounds

-does  not enter atmosphere (only as dust(

*acidity greatly affects the availability of phosphorus to plants

-when acidic, it binds tightly to clay particls and becomes insoluble

-is part of 2 amino acids... cysteine and methionine... required by life

-exists in many forms, most oxidized is sulfate (SO4) and most reduced forms are H2S and organic forms

-reduced sulfur may be used by photosynthetic bacteria to assimilate carbon by pathways analogous to photosynthesis in green plants

-elemental sulfur accumulates unless the sediments are exposed to aeration or oxygenatd water, at which state it may be oxidized by chemoautotrophic bacteria to sulfite and sulfate

-without nitrogen fixing bacteria, denitrification uder naerobic conditions would slowly deplete ecosystems of available nitrogen and reduce biological productivity proportionally.

photoautotrophs use sunlight as their source of energy. all green plants and algae are photoautotrophs, as are cyanobacteria, which use water as an electron donor (reducing agent) and are aerobic; and purple and green bacteria, which have light absorbing pigments different from those of green plants, use H2S or organic compounds as electron donors, and are anaerobic

chemoautotrophs- all use CO2 as a carbon source, but they obtain energy for its reduction by the aerobic oxidation of inorganic substrates: methane; hydrogen; ammonia; nitrite; hydrogen sulfide, sulfur, sulfite; or ferrous iron salts.

-almost all bacteria

HYDROTHERMAL VENTS

-the deep sea vents occur well below the level of light penetration, and so there can be no photosynthesis

-the water is hot, and loaded with reduced form of sulfur, H2S

-this is ideal for chemoautotrophic bacteria

-they use oxygen in seawater to oxidize hydrogen sulfid in vent water

-this oxidation provides a source of energy for the assimilatory reduction of inorganic carbon nd nitrogen in seawater

-nutrient regeneration in terrestrial ecosystems occurs primarily in the soil

-new nutrients arrive through the formation of soil by weathering of bedrock and other parent materials

-can measure weathering by measuring the net loss of certain elements from a system

-loss of element from a system equals a weathering input

a watershed is the entire drainage area of a stream or river, from which all surface water and groundwater leaves at a single point

-best known watershed study comes from the Hubbard Brook forest.

-typically, weatering of bedrock provides only 10% of the soil nutrients taken up by vegetation each year

-rain gauges are used to measure nutrient inputs

-analyses of teh nutrient content of water colleced in them helps to determine the overall nutrient budget of the forest and the specific routes of mineral cycles.

-stream gauges are used to measure nutrient outputs

-plants assimilate elementsfrom the soil far more reapidly than weathering generates them from parent material

-organic detritus is everywhere, most conspicuously in terrestrial habitats, where parts of plants are not consumed by herbivores accumulate at the soil surface, along with animal excreta and other oranic remains

Breakdown of leaf litter on the forest floor occurs in four ways:

1)leaching of soluble minerals and small organic compounds by water

2)consumption by large detritus feeding organisms (millipedes, earthworms, wood live)

3)breakdown of the woody components of leaves by fungi

4)decomposition of almost everything by bacteria

-association of fungus and root that enhances a plant's ability to extract mineral nutrients from soil and greatly increases primary production, especially on poor soils

-types are endomycorrhizae and ectomychorrhizae

-promote growth in nutrient depleted soils

-may also protet plant roomts from disease

-most species of vascular plants have endomycorrhizae

-they stimulate growth under low phosphate conditions, but not under high phosphate conditions, as other nutrients become limiting

-ecto- types may extend far out into the soil and may be responsible for taking up organic forms of nitrogen, esp ammonium, that pants are otherwise incapable of using

-high productivity of tropical areas is supported by

1)the rapid decay of detritus uner warm, humid conditions

2)the rapid uptake of nutrients by plants and other organisms from the uppermost layers of soil

3)the efficient retention of nutrients by plants and their mycorrhizal associates

-over extensive regions of old, deeply weathered soils in teh tropics, planting crops such as corn on clear-cut land has predictable adverse consequences for soil fertility

laterite - as exposed tropical soils dry out, upward movement of water draws irons and aluminum oxides toward the surface, where they form a bricklike substance called laterite

-the practice of cutting and burning felled trees releases many mineral nutrients, which may support 2-3 years of crop growth, but then they are quickly leached

-eutrophic , or "well-nourished" soils develop in geologically active areas where natural erosion is high and soils are relatively young

-with bedrock closer to the surfaec, weathering adds nutrients more rapidly and soils retain nutrients more effectively

- in contrast, oligotrophic , or nutrient-poor soil develop in old, geologically stable areas, particularly on sandy alluvial deposits (Amazon basin) where intense weathering removes clay and reduces teh capacity of soils to retain nutrients

-productivity in aquatic ecosystems is highest where nutrients regenerated in sediments can reach the photic zone

-productivity is greatest on continental shelves and in regions of upwelling

-sunlit areas are often removed from nutrient areas

-anaerobic areas result in poor decomposition in large bodies of water

THERMAL STRATIFICATION HINDERS VERTICAL MIXING

-lakes at low and high latiudes experience little thermal stratification

-lakes at middle latitudes experience more

-on one hand, mixing can bring nutrient rich water rom the depths to the photic zone and thereby promote production

-on the other hand, mixing can carry phytoplankton below the photic zone and thereby reduce production

-when a body of water is stratified with a thermocline, highest productivity occurs along thermocline 

-iron and silicon can be limiting agents in ocean environments with abundant phosphorus and nitrogen

 -in southern hemisphere, this is the case, with silicon lacking

-when O2 runs out in anoxic lake conditions, bacteria resort to using sulfur as an oxidizing agent (is reduced) in the place of oxygen

-results in H2S

*oxygen depletion in teh hyplimnion changes water chemistry!!!

-oxygen reduces, carbond dioxide increases, iron/phsphate fluctuate lots, ammonia increases dramatically, and nitrate decreases

-then, mixing occurs in early fall

-phosphorus is the most important contributor to the fertility of most lakes, and low levels of phosphorus limit production

-experiments in natural lakes demonstrated the crucial role of phosphorus in europhication (Schindler)

eutrophication - overproduction of organic matter within a lake or river can elad to imbalance when natural regeneration processes cannot handle the increased demands for cycling of organic matter

-heavy organic pollution, which results, for example from dumping raw sewage into rivers and lakes, creates biological oxygen demand, resulting from the oxidative breakdown of organic detritus by microorganisms

-in the worst conditions, everything in the lake can suffocate

-high external and internal nutrient input makes estuaries and marshes highly productive

-salt marshes export energy to other marine ecosystems

-whale populatons were decimated during the nineteenth and 20th centuries

-when one became unprofitable, switched to something else

-sardine fisheries collapsed in the 50s, only to be replaced with anchovies

-fishing,hunting, grazing, fuelwood gathering, logging, and the like

-technology has advanced too rapidly for nature to keep pace

-in many parts of the world, aggriculture and grazing has left the local land unproductive

-productivity of the tropics depends on natural vegetation

-"shifting agriculture" can be a sustainable pratice, whereby small farms can provide much of a family's food requirements without overstressing the environment

-estimated 50k nonindigenous speceis have been introduced to the USA

-40% of endangered species in US are threatened by competition or predation

-NZ is an extreme example

-500/2500 species are introduced, and account for most of the vegetation

-keystone predators introduced can have HUGE effects... (uneven top down effect)

-may increase soil erosion, and decrease productivity ofland

-on prairies, plowing destroyed the dense root mats of perennial herbs that formerly held the soil together

-drought in USA in 20s/30s turned former prairies converted to agriculture into a devastated "dust bowl" of blowing soil

-we are increasing out dependence on chemical fertilizers

-estimates indicate that up to 1% of the earth's topsoil is lost to erosion every year

-where mangrove forests have been cleared, coasts have been laid bare to rampaging hurricane driven floodwaters (storm surge)

-tremendous benefits and costs

-

COSTS
-environmetnal effects of developing teh dams, wells, canals, and dike work required to support irrigation;

-lowered water tables where wells are the source -

-reduction of groundwater quality through the introduction of pesticides and fertilizers or the concentration of naturally occurring toxic elements

-the accumulation of salt in irrigated soils in arid zones

-transmission of diseases by aquatic organisms

-any substance that enhances the productivity of a habitat may be considered a fertilizer

-can cause eutrophication in lakes/rivers

-input of organic wastes can create anoxic conditions in aquatic environments

-toxins are poisons that kill animals and plants by interfering with their normal physiological functions.

-can be natural or anthropogenic

ACIDS

-acid mine drainage-surfur bacteria oxidize pure sulfur and thiol forms of sulfur to fulfates, which may then be converted to sulfuric acid in streams that drain mining areas

-sometimes aquatic environments are sterilized

-acid rain is an even more widespread problem

-burning coal and oil produces nitric and sulfuric acid, esp in humid conditions

-pH as low as 4

HEAVY METALS

-low concenrations of mercury arsenic, lead, copper, nickel, zinc, etc are toxic to most forms of life

-usually introduced as refuse from mining, fungicides, adn burning leaded fuel

ORGANIC COMPOUNDS

-nicotine and pyrethrins are used as agricultural pesticids

-lots of organic pesticides are also produced in labs

-DDT, lindane, chlordane, etc

-

**bioremediation is the use of biological agents to clean up the environment and help restore habitats

-oil spills are another toxic effect

-mostly made of hydrocarbons

-most spills occur at source areas

-also in the ocear (drilling and tanker spills)

**ocean spills are most common!

RADIATION

-nuclear powerplants pose huge potential accidents

-Chernobyl '86, and Pennsylvania '79

-