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equal: local richness = regional richness

unsaturated (type I): dispersal limited, regional richness > local richness

saturated (type II): biotically limited; local richness largely independent of regional richness

a species must be able to coexist and thrive in a biotic community - must have tolerable relationships with other species within the community

- predators and competitors

a species niche comprises of the resources and conditions it needs to survive

- individuals do not compete for abiotic conditions

- a resource is anything that is limited in supply which will be unavailable to others after its use

shift to another resource

shift to anotehr habitat

- good colonizer

- good at resisting predation

- good at recovering from herbivory

some species make it easier for other species to exist in the environment

ex. clovers are nitrogen fixing and allow grass to grow well

- species run out of resources

- other species consume their resources

- disturbances occur

studies patterns of emigration, extinciton, speciation, and immigration that affect population structure

closed population dynamics: only studies extinction and speciation

populations reproduce in synchrony at regular time intervals and maintain non-overlapping generations. The growth rate stays the same

N_t = N_o x λ^t

- λ = 1: constant population size

lambda is the finite rate of increase

populations reproduce not asynchronously and reproduce continuously. Generations can overlap. 

N_t = N_o x e^rt

- r = 0; constant population size

dN/dt = rN ; r is constant, N changes

r = intrinsic rate of increase

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As density increases, r, the intrinsic rate of increase, decreases. Can be due to an increase in per capita death rate or a decrease in the per capita birth rate.

population size is a dynamic equilibrium and K serves as the balance between birth and death rates. 

Established when r=0 and λ=1

dN/dt = rN ( 1- N/K)

- density dependent growth

- describes the slow in population growth as the # of individuals in the population appraches carrying capacity

- a modification of the exponential growth equation

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Is an S-shaped curve with the slope of r. R decreases as density increases because resources such as food, water, or space begin to run short as the population appraoches carrying capacity

density dependent: regulates population size and results in an equilibrium

density independent: limits population size and results in a smaller populatoin at any given point; but no equilibrium

the per capita amount of productive land required to support one individual

neither regulates nor limits population size. Leads to a populatoin crash or explosion. 

- allee effects: at low densities, individuals have difficulty finding mates so per capita reproduction drops; theatens small populations

- instraspecific facilitation: the first few individuals increase survival or recruitment of the rest. Per capita rate increases with density

intraspecific: in between the same species

interspecific: between different species

exploitation competition

Species 1 equivalents =?

= N₁ + αN₂

- α: competition coefficient, the effect of species 2 on species 1

α > 1 : interspecific competition > intraspecific competition

α < 1 : intraspecific competition > interspecific competition

α = 1 : intraspecifc  competition = interspecific competition

- relate to the degree of niche overlap between competing species

- alpha and beta are independent of each other

- alpha and beta describe the relative effect of interspecific competition vs intraspecific competition on a species

assumes α = β = 1

- violates the competitive exclusion principle

limits biomass by causing patrial or total destruction

- can be biotic or abiotic 

reproductive output VS probability of survival

Reproductive Output

- when to reproduce

- when to stop reproducing

- energy to obtain mate

- how many offspring

- parental care

Probability of Survival

- how long to continue growth

- predator defenses

- disease resistance

- dispersal; when, how far?

- competitive traits

r- selected life strategy

- likely with continuous periodic disturbances

- disturbance results in catastrophic morrality independent of density

- irregular bursts of growth

- mortality dependent on density (regulating factors)

- favours individuals better able to cope with higher densities and strong competition

Primary productivity: does not differ between the two. Productivity pyramids show the same patterns.

Herbivory rates are higher in aquatic ecosystems than terrestrial. Results in biomass pyramids that are the inverse to one another. 

1) when the food quality is similar in atomic composition to their own bodies. They can easily breakdown food into simple molecules that can be absorbed. 

2) their food isnt poisonous os costly to consume

- animals typically consume other animals, which is very similar in atomic composition and stoichiometric ratios to their own bodies

carnivores are more efficient than herbivores because their food (animals) has similar nutirnet content to their own bodies. 

- lots of nitrogen and phosphorus, little carbon

- heterotrophs grow most efficiently when C:N and C:P ratios are low

plants typically have higher C:N and C:P ratios than animals

- higher carbon

- herbivores really only consume select plants with lower C:N and C:P ratios

aquatic plants are higher food quality because their C:N and C:P ratios are closer to that of animals that eat them 

ecological stoichiometry theory

Why do terrestrial plants have higher C:N and C:P ratios than aquatic plants?

Water supports plant tissues and air doesn't. Terrestrial plants require more structural compounds for support.

Aquatic plants have a closer stoichiometric match to their herbivores; do not require as many carbon-rich structural compounds. 

cellulose: major component of cell walls - 33% of terrestrial plant biomass

lignin: secondary strengthening of cell walls, water transport - 25-33% of wood. 

animals never evolved the digestive enzyme for cellulose or lignin.

- many terrestiral herbivores contain bacteria in their digestive tract that breaks down these compounds for them. 

- phylogenetic constraint

Either grow, or produce wood. 

ex. a eucalyptus tree either grows fast or grows strong

accounts for much of standing plant biomass and is mainly cellulose and lignin

- not very edible

- in many ecosystems, up to 70% of biomass is wood. Animals that appear to eat wood usually aren't - they are just getting it out of the way

Can termites eat wood?

herbivores consume much more of aquatic than terrestrial primary production. 

- due to differing C:nutrient ratios

1) the same

2) aquatic

3) terrestrial

Why are terrestrial ecosystems more accurately "green and brown"?

spines

resin and latex

trichomes

Usually involve a mutualistic relationship between plants and another species which protects the plant from herbivory

ex. Acacia trees associated with ants that repel herbivory by elephants. 

- complex molecules

- permanent

- expensive to make but no cost thereafter

- occur in high concentrations

- reduce digestability 

ex. tannins, polyphenols, fibre

- small water soluble molecules

- short lifespans, sometimes only hours

- cheap to make, but need to be constantly replenished

- occur in low concentrations

- poison herbivores

ex. alkaloids, terpenoids

the lifespan of the plant tissue

short lifespan: choose qualitative

long lifespan: choose quantitative

When using qualitiative chemical defenses, increased chemical production in response to herbivore damage can save investment in production of defense for when it is most needed. 

side note: induced defenses can prevent/reduce consumption by generalists (even when there is nothing to eat) but specialists that feed on the plant are typically not affected. 

- evolutionary arms race b/w predator and prey

- when the plant is likely to be found by a herbivore

- when the plant doesn't have enough resources to replace damaged tissue

K selected: predictably present so herbivores can find it easily. There is a resource limitation, so its difficult to replace lost tissue. Slower growth

solution: high investment in defense (esp. quantitative)

R- selected: this population appears and disappears rapidly, so difficult for herbivores to locate. Abundant resources allow plant tissues to be easily replaced. Faster growth

solution: low investment in defense (just qualitative)

most aquatic plants are unicellular algae with >50% of the ocean's productivity composed of picoplankton (smaller than 0.001mm)

- increased surface area for photosynthesis, less competition

- lighter, don't sink 

terrestiral plants have to grow up and down due to competition for nutrients and light. 

lower tropic levels limit higher trophic levels

plant quality ----> herbivore efficiency ----> herbivore abundance

Herbivore abundance is limited by food availability at lower trophic levels. Increases in plant quality or quantity leads to an increase in herbivore abundance

when higher trophic levels limit the abundance of lower trophic levels

plant quantity or quality --[+]--> herbivore abundance <--[-]-- predators

when there is top-down control, increases in predators reduce herbivore abundance. If increased predators result in fewer herbivores then the total amount of herbivory will decrease.  

predators have a positive indirect effect on plant biomass

Indirect top-down effects are called trophic cascades. 

Discusses limitations for a 3 level trophic system applied mostly to terrestrial systems

• predators don't expand indefinitely because they run out of food
• herbivores don't expand indefinitely because they get eaten
• 
  plants don't expand indefinitely because they run out of food

- increased productivity means that there is more total biomass entering the system via primary producers. 

- strong bottom-up control

- more trophic levels

Hairson and Hairson Hypothesis 2:

In aquatic ecosystems, larger organisms consume smaller organisms by engulfing them. Distinct trophic levels. There should be 4 trophic levels in aquatic ecosystems resulting in lots of herbivores and few plants. 

In terrestrial ecosystems, engulfment is rare and predators can either be bigger or smaller than their prey. All predators are omnivorous and should be considered one trophic level. There should be 3 trophic levels, few herbivores and lots of plants. 

1) aquatic food webs should have more trophic levels than terrestrial food webs (4 vs 3). observations: Marine and lake ecosystems have the most trophic levels. 

2) Terrestrial food webs should ahve more omnivory than aquatic food webs. Not true. Marine ecosystems have the most omnivory; terrestrial systems have intermediate levels of omnivory

What really determines the number of trophic levels between ecosystems?

Ecosystem size

Larger ecosystems have more trophic levels than smaller ecosystems. 

ex. larger lakes have more trophic levels because:

- species like trout can be supported, that feed at a higher trophic level

- within a fish species, individuals in larger lakes feed on higher tropic level prey - there is less omnivory

Using herbivore and plant log ratios.

herbivore log ratio = log (herbivore biomass w predator/ herbivore biomass w.o predator)

plant log ratio = log (plant biomass with predator / plant biomass w.o predator)

The larger the ratio, the stronger the effect of the trophic cascade (indirect effect)

Which system, ultimately, has stronger tropic cascades?

aquatic

Terrestrial food webs have weaker trophic cascades due to poor plant quality which leads to low herbivory. If there is little herbivory to begin with, reducing it further will not have a very significant impact on plant biomass. 

Aquatic invertebrates and ectotherms dominate food webs; more efficient physiology permits higher growth rates which allows them to quickly depress prey populations. 

biological processes that involve the flow of energy and nutrients in, out and through food webs

- carbon fixation

- water purification

- pollination

- decomposition

- pest suppression

- production of biomass

- nitrogen fixation

- energy flow through food webs 

Animals: large body sizes, K-selected life-histories, higher trophic levels, specialists

- more sensitive to change, not tolerant of disturbance

Plants: endangered plants depend on the exact stressor

- habitat fragmentation particularly affects poor dispersers

- global warming particualrly affects C4 grasses (via CO2 change) and shallow rooted species

1. habitat loss and fragmentation
2. overharvesting
3. pollution (including N deposition)
4. invasive species
5. climate change

(1) is currently the most imporant

- most of the world has experienced substantial loss of native habitat

habitat loss: conversion of an ecosystem to another use

habitat degradation: changes that reduce quality of the habitat for many, but not all, species

habitat fragmentation: breaking up of continuous habitat into patches amid a human-dominated landscape

there is a continual increase in the number of introduced species which leads to biotic homogenization of the world

- species introductions usually never corerlates with increased biodiversity, usually decreases it

ex. the Nile perch introduced to Lake Victoria drove as many as 200 cichlid species extinct

The threat to high trophic levels

- bioaccumulation; toxins that bind to organic matter tend to accumulate at higher trophic levels

- bottom up assembly of food webs

- small reduction at bottom = large reduction at top

- economic gains and environmental losses are not under the same currency

- many ecological losses are economic wins

- no common currency between losses and gains

$195 billion for global agriculture

- crops that depend on pollinators have lower and less predictable yields than those that dont. 

- pollinator diversity is declining rapidly

- distribution of bee-dependent plants is also declining

Wild pollinators improve flower visitation and fruit set more than honeybees. 

- wild pollinators cross-pollinate more resulting in more fruit set

- honeybees tend to visit the same flower twice

More diverse pollinator communities visited flowers more often, resulting in more fruit set and increased productivity. 

$ 7 billion

biodiversity improves water quality through niche partitioning

wetlands provide more filtering of water

Ecosystem value: Carbon Fixation

In the $$TRILLIONS$$

Terrestrial plants sequester 2.6x10⁹C per year, offsetting 30% of atmospheric carbon emissions

Most experiments show that plant diversity increases plant production, which increases carbon fixation. 

Economic prosperity depends on predicatble rates of return on investment

Increasing biodiversity is proven to increae ecosystem properties such as consumptive resistance and invasion resistance. 

Biodiversity increases ecosystem functioning and stbaility. 

Ecosystems are able to maintain stability but the risk of catastrophic failure increases with increased loss of species. Loss of biodiversity is like losing rivets on an airplane. 

- due to niche complimentarity

Species need to be different so that they can coexist. 

They complement each other in terms of the type and location of the resources they consume. Compliment each other functionally. 

A diverse community is more efficient as a whole at extracting resources than a monoculture. 

species may help each other with function. 

For example, clovers fix nitrogen which grasses use for biomass production. 

- a field with both clover and grass is more prouctive than one with just one of the species

- farmers often intercrop to get higher yields

Could be argued that the biodiversity- ecosystem function relationship simply occurs because of probability, not biology. Just keep a key species from going extinct and biodiversity doesn't matter. 

problem: we can't predict which is the key species

- everytime we lose a species from an ecosystem we risk losing the best monoculture 

If species fluctuate independently, the net biomass (or fucntion) of a diverse community may not fluctuate much as individual fluctuations may cancel each other out. 

More diverse communities may have lower variability than depauperate communities. 

Concerns of Biodiversity Experiments

1) small, homogenous plots in experiments does not resemble real world. 

- not a problem. adding realistic amounts of spatial heterogeinty strengthens the BDEF relationship

2) most BDEF experiements based on random loss

- no, we know that extinctions aren't random. Certain species (i.e. k-selected) go extinct first

- functionally important species often the most important

3) we could optimize carbon sequestration by replacing native forests with eucalyptus monocultures

false. true for only one function. If we consider optimizing multiple ecosystem functions, there is no ideal monoculture. 

What are these equations?

N_t = N_o x e^rt

r = log_e (N_t/N_o)/t

The human population per capita intrinsic rate of increase of impact on global change. 

Per capita impact and global change all show approximately exponential growth. 

eutrophication of aquatic systems, eventually leading to anoxia and plant death

pollutio of ground water with nitrates

loss of plant species richness as a few N-loving species outcompete the rest

Anthropogenic effects = source

- only outputs

ocean sediments = sink

- only inputs

SINKS

deep ocean

atmosphere

vegetation and soil

surface ocean

SOURCE

fossil fuel use

land use change

- greenhouse effect

- decreasing ocean pH (ocean acification)

CO2 dissolves into the ocean at the sea surface. As water cools, it can hold more dissolved CO2 and sinks deep. If these deep waters upwell, the CO2 will come out of solution. 

physical pump: H+ is continuously released as CO2 dissolves and breaks down in the ocean

biological pump: phososynthesis in surface waters fixes dissolved CO2 into organic carbon

- calcium shells use bicarbonate in the water from the CO2- water reaction

- only a fractin of this carbon and calcium carbonate shells sediment - remaining is released as dissolved CO2

ocean acidification

sea ice melting

ocean temperature increase

loss (extinction) of predators from 3 level food webs

- decreased calficiation in corals

- decreased photosynthesis in aquatic ecosystems. Unlike terrestrial ecosystems, CO2 does not fertilize marine plants (photosynthesis unchanged or lowered)

dramatic shifts in habitat

altitudinal range shifts

latitudinal range shifts

extinctions when species can't move or evolve fast enough

ocean warms ----> less phytoplankton -----> less C fixed in ocean -----> ocean warms ------> 

reduces the ocean's sink property