BIO 182 Exam 3

ecology

the study of interactions of organisms with one another (biotic) and with the environment (abiotic)

levels of ecology

individual < population < community < ecosystem < biosphere

population

• a group of individuals that can interbreed and produce fertile offspring (belong to the same species)

• living in the same/defined area

• at the same/defined time frame

species, area, time

population ecology

focuses on interactions within a population and how these interactions affect population size, where organisms live, and the factors that limit their growth

characteristics of a population

1. population size/abundance

2. population density

3. range of a population

4. distribution pattern of individuals

5. sex ratio

6. age structure

population size/abundance

the total number of individuals in an area

drivers of population size

+: birth, immigration

-: emigration, mortality

EQUATION: change in population over time

∆N = (B - D) + (I - E)

∆N: change in population size

B: number of births

D: number of deaths

I: number of immigrants

E: number of emigrants

population density

total number of individuals in a unit area or volume

D = n/A

range of a population

spatial extent or distribution area where individuals of a species live, feed, reproduce, migrate

importance of population size

assessing extinction risk

tracking population growth or decline

importance of population density

determining local ecological impact of a population

understanding crowding, competition, disease transmission, and how often individuals encounter one another

importance of population range

identify the conservation/management goals of a species and its associated habitats

distribution pattern of individuals

pattern of how individuals in a population are spread out across their habitat

mainly driven by resource availability and sometimes species-specific behavior

clumped/patchy, uniform, random

importance of distribution pattern

resource and disease outbreak management; creating protected areas

clumped/patchy distribution

• most common form

• usually occurs where resources are concentrated

• sometimes social/group behavior results in clumped

uniform distribution

• individuals are evenly spaced from each other

• usually even distribution of resources

• animals defend territories with just enough resources and space out enough to minimize aggression

random distribution

• no predictable pattern; individuals are scattered

• resource distribution is unpredictable

sex ratio

ratio of males to females

importance of sex ratio

• skewed ratios result in unstable population

• determines mating strategies (monogamy, polygyny), social structure, territorial behavior

• important for effective conservation and management practices

age structure

the proportionate numbers of individuals in different age categories in a given population for a defined time

importance of age structure

helps ecologists to:

• set hunting or fishing limits

• design protected breeding areas

• plan for species reintroduction

pre-reproductive

higher proportion of young individuals

likely to grow in the future

reproductive age structure

current population growth

post-reproductive

higher proportion of older individuals

may decline over time

pattern of population growth

actual number of individuals added to or lost from a population over a given time

EQUATION: per capita growth rate

r = (ΔN/Δt) / N₁

EQUATION: predicting the future population size

N_t+1 = N_t + r(N_t)

r in exponential growth model

constant

EQUATION: exponential growth rate

N_t = N₁ (1 + r)^Δt

end population after a certain time frame

what is a density dependent factor

the impact of the factor changes as the population density changes

density dependent factors

competition, predation, parasitism, infectious diseases

what is a density independent factor

the impact of the factor is not influenced by population density

density independent factors

natural catastrophic events

climate change or human caused events

carrying capacity (K)

the maximum number of individuals in the population that a given area can sustain

how does r change at different points with logistic growth model

when N = K, r = 0

when N = 1/2K, r is max

EQUATION: logistic growth model

N_t = N₁ + rN₁ ((K - N₁) / K)

community

a group of organisms found in the same geographic space at the same time

may/may not be the same species

boundaries are not clearly defined

characteristics of communities

1. species diversity

2. trophic structure

3. types of interactions

4. stability

species diversity

describes the variety of species in a community

diversity is highest with more species and when they are equally abundant

measures of species diversity

species richness

species eveness

species richness

the total number of different species in an area

species evenness

how evenly individuals are distributed among species

high evenness: if all species have similar numbers of individuals

low evenness: if one species dominates

trophic structure

the feeding interactions between organisms in a community (who eats whom)

autotroph

organism that produces its own food

heterotroph

organism that does not make its own food; consumers

food web levels

primary producer → primary consumer → secondary consumer → tertiary consumer

trophic cascade

the addition of removal of a species at a particular trophic level leads to a chain reaction

often results in dramatic changes in community structure and nutrient cycling

often related to removal/addition of top predator

keystone species

species within a community that have a greater impact on that community than any other species

interspecific interactions

• competition

• predation

• herbivory

• parasitism

• mutualism

• commensalism

competition

the interaction between organisms or species that compete for the same limited resources in a community

affects survival, growth, reproduction

can occur for food, space, mates, etc

types of comeptition

intraspecific: same species

interspecific: between species

competitive exclusion principle

two species that compete for the same resources cannot stably coexist in the same nice

one will eventually outcompete the other and eliminate it from that niche

niche

combination of a species physical habitat and ecological role

the role in the community and how it interacts with the environment

habitat

the place where an organism lives

where an organism finds its food, shelter, and mates

fundamental niche

includes the full range of habitats that permit the individuals in a species to play their specific role in the community

realized niche

the actual range of habitats occupied by a species while playing its specific role in the community

resource partitioning

a consequence of competitive exclusion: species with initially similar niches diverge in resource use

niche differentiation

evolutionary process by which competing species develop different niches over time

explains how and why resource partitioning happens

predation

individuals of one species (predators) feed on, and directly harm, individuals of another species (prey)

carnivory

predator and prey are animals

herbivory

predator is an animal, prey are plants or algae

differences between carnivore and herbivore

• carnivores kill their prey; herbivores usually don’t kill plant

• plants are more abundant but have lower nitrogen content and are less nutritious

• generalists vs specialists

predator adaptations

speed, toxins, sharp teeth, camouflage

optimal foraging

predators developing physical, physiological, and behavioral counteradaptations for prey capture

predator-prey adaptations

large size, rapid/agile movement, body armor

prey adaptations

behavior (foraging less in the open) or keeping lookouts

crypsis/adaptative defense

hiding in plain sight

chemical defense/aposematism

species contain toxins and are brightly colored as a warning

some predators can detoxify or tolerate specific prey chemical defenses

mimicry

palatable mimetic species resemble an unpalatable model species

physical plant defense

spines, fibers, hooks, crystals

chemical plant defense

tannins (reduce leaf palatability), nicotine, caffeine, strychnine, distasteful or poisonous

some herbivores store and use toxic plant compounds for their own defense

parasite

consumes the tissues or body fluids of its host

pathogens

parasites that cause diseases

all pathogens are parasites; not all parasites are pathogens

completely parasitic parasites

obtain all nutrition from hosts

partially parasitic/hemiparasitic

only part of nutrition from host

ectoparasites

live on outer body surface of the host

endoparasites

live within the host, in the alimentary canal, or within cells or tissues

most disease organisms are endoparasites

defense mechanisms of hosts against parasites

• protective outer coverings (skin, exoskeletons)

• vertebrate immune systems have memory cells that can recognize microparasites from previous exposures

• other immune system cells engulf and destroy parasites or mark them with chemicals that target them later for destruction

counterdefenses against parasites

some animals eat specific plants to treat or prevent parasite infections

ex: caterpillars switching to poison food when parasitic flies lay eggs on their body; chimpanzees eating a plant that contains chemicals that kill or paralyze a specific parasite

parasite-host coevolution

populations of two interacting species evolve together, each in response to selection pressure imposed by the other

when parasite and host each possess specific adaptations, it suggests coevolution

enslaver parasites

change host behavior

ex: cordyceps fungi in ants

negative species interactions

predation, herbivory, competition, parasitism

positive species interactions

cooperation, symbiosis, mutualism

one or both species benefit and neither is harmed

allow organisms to live in places where they would otherwise be unable to survive

commensalism

individuals of one species benefit; individuals of the other species do not benefit but are not harmed

+/0 relationship

common instance of commensalism

species form a relationship with organisms that provide habitat

symbiosis

two or more organisms existing in close association

can be (+ / -), (+/+), (0/+), (0/-), (0/0)

mutualism

mutually beneficial interaction between individuals of two species

+/+ relationship

important for generating biodiversity

obligate mutualism

necessary association required for the survival and reproduction of both species

facultative mutualism

beneficial but not essential for survival and reproduction

lichens

mutualism between fungi and algae, many of which can fix N₂

→ obligate for many of the fungal components

currency of mutualisms

food, protection, transport

protective mutualism

mutualist provides shelter, physical protection, or chemical/immunological defense

ex: ants protect plants from herbivores and/or protect herbivores from their natural enemies

nutritional mutualism

mutualist improves nutrition or confers access to a novel limiting resource

provide a limiting nutrient for insects on nutritionally poor or unbalanced diets

dispersal/transmission/transportation mutualism

• dispersal of reproductive propagules (seeds)

• transmission of pollen

• transportation of individuals

benefits of pollination (4)

1. plants are rooted and can’t seek partners

2. plants gain higher rates of gene exchange among compatible partners

3. animals gain a source of food and energy

4. each inadvertently assist the other

cheaters

seek to obtain the reward while not providing any services in return

disturbance

• can be normal part of healthy ecosystems

• modify community composition

• diverse communities recover fast from disturbances

ecological succession

process of changing communities and their environments at a specific location over time

species turnover

the change in species identity as some species arrive or become established and others disappear from a community