ecology unit test 3

Assumptions of the Lotka-Volterra Predator/Prey Model

• 2-species model: predator & prey, prey death means eaten by a predator so it is proportional to predator growth, infinite prey food

• these #s can vary continuously

  • (atto fox problem: @ a low enough density is extinct)

• any predation event has the same population effect: eating old, young, diseased, weak, or parent is all the same

General inputs of the Lotka-Volterra Predator/Prey Model

prey: change in prey pop = exponential prey growth - attack rate(prey pop)(exp pop)

a.k.a. change = prey growth rate - prey death rate

• if attack rate is low, there needs to be a lot of exploiters to have an effect

• if exploiter pop is low, they need to eat a lot to have an effect

• a large prey death rate could balance the exp growth

exploiter: change in exp pop = (conversion efficiency)(exp birth rate) - exp mortality*pop

a.k.a change = f(prey death rate) - exp mortality * pop

• exploiter birth rate includes prey pop, exp pop, attack rate, & efficiency of turning prey into babies

• just assuming, a standard death rate based on pop

Connection between Cycle graph and Linear graph of Predator/Prey Model

mutualism

both species acting in a way that benefits both (+,+)

• fruit as seed dispersal (typically interspecific)

difference between obligate & facultative mutualism

obligate is necessary for survival

facultative is not necessary for survival

altruism

individual decreasing own fitness to boost another (-,+)

• kin selection, parental protection (typically intraspecific)

Strategies of the Prisoner's Dilemma

1. naive

• strategy: always cooperate

• gets taken advantage of by selfish

2. selfish

• strategy: always deflect

• great against naive, low payout against selfish

3. tit-for-tat

• strategy: starts cooperating, then copies partner

• success w/ naive, not taken advantage of by selfish

• succeeds w/ other TFT

  • stable strategy!

Conditions for cooperation

• benefits for cooperation are greater than benefits for selfishness

• interactions are repeated, single interactions encourage selfishness

  • cheaters are punished: “do no harm but take no crap” , defectors don’t get the benefit of cooperation

richness

count of species in an area

3 types of richness

alpha diversity: local richness

• # of species in sample site (a part of a region)

gamma diversity: regional richness

• total # species across multiple sample sites (region)

beta diversity: richness variation

• differences of species between sites

  • beta = gamma/alpha

eveness

how close in abundance each species is (proportion of individuals that are that species)

functional diversity

variety of ecological “roles” present in an ecosystem

• “roles” are most often described by an organism’s space in the food web

phylogenetic diversity

variety of clades present in an ecosystem

• concern if extinction of phylogenetically distinct organisms

Shannon-Weiner Diversity Index implications

diversity index = - sum of relative abundance*ln(RA)

• increases with both richness & evenness

migration

back-and-forth movement between specific areas

• often between feeding sites & breeding sites

• driven by cyclical differences in food availability or different survival requirements of young & adults

dispersion

one way movement to a new area, typically of few individuals

difference between natal & breeding dispersion

natal: movement from birthplace

breeding: spread as new adults & find suitable locations

Island biogeography equilibrium

we expect an island to have a # of species based on rate of colonization & extinction

• as species richness inc, successful colonization dec (fewer free niches) & extinction inc (more things to go extinct)

• crossover point is stable richness

• the smaller the island, the higher extinction rate

  • the closer the island the higher colonization rate

succession

change in species composition of a community over time

(recover from a disturbance)

primary succession

a community starting from nothing

• life pioneering into a new space

• volcanoes - lava, ash beds, new islands

secondary succession

a community starting from something

• dirt, small plants, bugs, typically still there

• fires, floods, cutting

  • “resetting to earlier stage”

pioneer species

in primary succession comes from elsewhere to change environment to be suitable for other organisms

climax community

“old growth” where a community reaches stable state

• ex: big tree

non-native

moved (intentionally or not) by humans (alien, exotic, etc.)

invasive

successful in human disturbed areas

• often a species in an area where it causes ecological harm (reducing diversity)

why species are invasive

• brought as a non-native by humans to an area

  • thrive in new areas that lack native predators

climate predictors (4)

• Latitude: hotter year round the closer to the equator

• Atmospheric cells: hot/wet air rises in the equator, cools & drops rain, gets pushed 30 deg N&S, drops & heats, gets pushed back to equator, repeats

• Coriolis effect / Ocean currents: earth’s spin sets up a wind direction w/ help from atm cells, wind direction determines ocean current direction which moves large amounts of hot/cold water to a landmass & affects its climate

• Rain shadows: warm/wet air pushed up a mountain, air cools & drops as rain, no moisture in air on far side of mountain, causes deserts

climate change (3)

• Greenhouse effect / greenhouse gas: molecules in the earth’s atm (h20, co2, methane, nitrogen oxides) reflect infrared radiation to the surface which inc surface temp

• Hothouse (no ice caps or glaciers) / Ice Age (fluctuate between glacial (ice sheets/glaciers inc) & interglacial (ice sheets/glaciers dec))

• Effects of Anthropogenic Climate Change: burning fossil fuels for energy (easiest/highest density energy source), industry increasing CO2 levels

  • causes issues: oceanic acidification (dissolve shells), sea level rise (flood), weather changes (droughts, severe storms, change air/water currents)