Ecology- Final Exam

Requirements of a community

1) a group must have more than 2 species

2) the species must interact (directly or indirectly)

PCA plots

condense multidimensional data in two axes. points that are closer together have more similar communities

Species richness

number of species present (abundance of each species doesn’t matter)

Alpha diversity

measure of local diversity at a single site; can be described by richness (S), evenness (Shannon’s E), both richness and evenness (Shannon’s H)

Beta diversity

measure of local diversity; comparison between sites; Sorenson’s S

Gamma diversity

regional diversity (all species pooled together); can be described by richness (S), evenness (Shannon’s E), both richness and evenness (Shannon’s H)

Evenness (Shannon’s E)

takes into account the abundance of species; higher evenness means higher community diversity and more even distribution of species; measured by Shannon’s E

Shannon’s H (Shannon’s index)

measures both species richness and evenness; measured for a single site; a higher Shannon’s index means higher diversity (accounting for both richness and evenness); higher values mean more community diversity

Sorenson’s index

measures community differences (similarity) between two sites; Higher Ss means more overlap between sites and higher similarity and thus lower community diversity in the area; if two sites have exactly the same species then Ss = 1; higher dissimilarity means higher Beta diversity

Communities

groups of interacting species that an ecologist is interested in studying

In species accumulation curves, how to know which line has more diversity

More increase in steepness of slope and levels off later

Two types of interaction webs

1) in some diagrams (particularly those showing trophic levels), arrows will point in direction of energy flow, and lack plus/minus signs

2) in other diagrams (particularly those showing horizontal lines), arrows will point in direction of effect, and include plus/minus signs; can include interspecific interactions such as competition and mutualism

Disturbance

any relatively discrete event in time that disrupts the ecosystem, community, population structure, and changes resources, substrate availability or physical environment

Succession

a directional change in species composition over time following a disturbance; ex. bacteria recolonizing gut after taking antibiotics

3 mechanisms of succession

Facilitation: early species modify environment, facilitate later species- positive effect of early species on late species; Inhibition: early species resist invasion of later species (any species that arrives first will establish)- negative effect of early species on late species; Tolerance: early species have no effect on later species

Top down effects

changes in abundance of species at higher trophic levels affect lower trophic levels; primary production increases if herbivores are excluded and decreases if herbivores are present, stays same with resources

Bottom up effects

changes in plants (base of food web) cascade up to cause effects on higher trophic levels; primary production stays same with herbivory, increases with high resources and decreases with low resources

Colonization-competition continuum

A species is usually good at colonization (invading empty environments) or competition, not both. This means it is usually harder to invade a diverse community than one with few species; ex. C.difficile

Where is diversity highest in the intermediate disturbance theory?

Diversity is highest at intermediate levels because this is where there is a balance between stress and competition. As disturbance becomes more frequent, competition decreases since stressors are high, and only a few individuals can survive these disturbances leading to lower diversity.

Keystone predator

when the presence of a predator increases community diversity; when keystone predator is present, superior competitor is suppressed and opens spaces for other species; ex. Piaster and sea otter

C.difficle example

good colonizer but a poor competitor, so it can only invade the human gut after antibiotics have wiped out the existing microbiome; fecal transplants are good because they restore the normal microbiota of a healthy gut which includes a diverse community and many good competitors, outcompeting C.dif and driving it to extinction

Metapopulations

populations of populations; are most relevant for very small patches and often used to describe rare/endangered species

Why does immigration peak at p = 0.5?

This is where there are lots of patches are available for colonists and where emtpy patches also receive colonists

What two processes does immigration (I) depend on?

1) patch sends out colonist

2) patch successfully receives colonist

What does extinction (E) depend on

“within-patch” dynamics; each patch has its own probability of extinction, and this does not depend on whether nearby patches are occupied or not; curve is a straight line because patches can only go extinct if they are occupied; if p is higher, there are more patches to go extinct

Equilibrium/optimum of occupied patches

occurs where immigration and extinction cross because this is where immigration to new patches balances extinction of old patches

3 main categories of climate impacts

1) impacts on physiology- wider performance curves mean that species can tolerate a wider range of temperatures, and thus less likely to be negatively impacted by climate change

2) impacts on distribution/species range- as temperature increase, species shift to cooler areas (higher altitudes/ “uphill” and more temperate climates/ “toward poles”)

3) impacts on phenology (species interactions)

Why are high altitude species more likely to go extinct from climate change?

because they have limited space to migrate to cooler areas and may face increased competition with species from lower altitudes

Phenology

timing of life history events like reproduction through calendar year; measured as shifts in sensitivity

Phenological mismatch

occurs if interacting species respond differently to climate change, disrupting the interaction; ex. one species emerges in the spring and the other one is not there yet

Tradeoffs

as one thing gets better, something else gets worse; ex. growth vs. reproduction; one reproductive event vs. multiple reproductive events

r-K continuum

r = intrinsic population growth rate or growth rate when population has unlimited resources; r- selected species do well when population densities are low; “live fast, make lots of babies, die young”

K = carrying capacity (max population density); k-selected species do well when population density is high so fewer resources shared among individuals; “live slowly, make a few babies and take good care of them, and die old”

Intrinsic per capita population growth rate (exponential)

growth rate under ideal (unlimited resource) conditions, r

Per capita population growth rate (exponential growth)

equal to the intrinsic per capita population growth rate, because exponential growth only happens under unlimited resources

Overall population growth rate (exponential)

per capita growth rate times your population size, for exponential growth = r*N, and keeps getting larger and larger as N increases

How to know whether plots show exponential growth?

population density rapidly increases over time due to unlimited resources (density independent)

When does logistic growth occur?

Due to intraspecific competition, as a population runs out of resources, its per capita growth rate decreases

Intrinsic per capita population growth rate (logistic)

growth rate under ideal (unlimited resource) conditions, r

Per capita population growth (logistic)

for logistic growth rate, this decreases with population density as the population runs out of resources and competition increases (r*(1-N/K))

Overall population growth (logistic)

per capita growth times the population size (dN/dt = r*(1-N/K)*N)). this starts out small because the population size (N) is small, then reaches its highest point when population is half the carrying capacity, then decreases to 0 as the population increases to the carrying capacity

competition

harms both species (-/- interaction); each competing species will always have a lower density in the presence of the other; competition is stronger the more limited a shared resource is; example: ants vs. crabs

Type I survivorship curve

high survival when young and middle aged, but drops off rapidly near end of life; more k-selected; ex. humans

Type III survivorship curve

very low survival when young, but individuals who survive past a certain stage can live a long time (survival stays relatively constant); more r-selected; sea turtles

Type II survivorship curve

somewhere in between; ex. birds

Parasitism (exploitation interaction)

lives in/on host and gets food/resources from its host; host is usually harmed but not killed (+/- interaction); example: mosquito vs. humans; can evolve from mutualism

Predation (exploitation)

one animal species (predator) kills and eats another animal (prey); always kills the prey (+/- interaction); example: wolves. moose

Herbivory (exploitation)

herbivore (animal) eats part of plant or algae; usually does not kill the plant (+/- interaction); ex: rabbits vs. grass

Parasitoids (exploitation)

live inside the host and must kill the host to reproduce; usually deposits offspring (eggs or larvae) into the host and the larvae eats their way out; (+/- interaction); ex. wasp vs. caterpillar

Competitive exclusion

one species persists, while other becomes (locally) extinct

Coexistence

favored when intraspecific competition is greater than interspecific competition; each species has a bigger effect on itself than on the other species; alphas are small and each species does not affect the other very much

Direct vs. indirect defense

direct defense = defend yourself (structural, chemical, physical, behavioral); indirect defense = “hire” someone else to defend for you, type of mutualism, victims recruit the predators of their own enemies to defend them, common in herbivory (ants and plants)

Induced vs. Constitutive defenses

induced = only produces defenses once you are attacked, good strategy when attacks are rare and/or defense is energetically costly; constitutive = produces defenses all the time, no delay before defense working, good strategy when there are lots of predators and high resources

what are alphas in lotka-volterra model?

are “conversion factors” telling us how many individuals of species 1 use up the same resources as one individual of species 2 (and vice versa)

what does a smaller k value tell you?

intraspecific competition is greater in a species

survivorship

per capita survival since birth

fecundity

mean number of offspring

Coevolution

each species evolves in response to the other; each species is the “selective” environment for the other; common in interspecific interactions

Predator-prey coevolution example

cheetahs vs. gazelle; each generation, the slowest prey gets consumed by the predators (fitness = 0) and the slowest predators fail to catch prey and starve (fitness = 0)