ecology exam 2

distribution (population)

where individuals are located

abundance (population)

how many individuals are present

population size (N)

total number of individuals

population density

number of individuals per unit area

how to calculate density from population size and area

Density = Population size ÷ Area

when populations differ in size and occupied area

a smaller population can have a higher density if it occupies a much smaller area.

why do counting visible stems not equal counting genetic individuals in a clonal organism?

One genetic individual can produce many stems/shoots. Therefore, many visible stems may actually belong to one genetic individual.

distinguish an estimate of total population size from a relative measure based on observations or sampling effort

absolute estimate: estimates the actual number of individuals.
relative measure: tells you how common something is based on observations or sampling effort, but not the total number.

what information does a measurement support? what additional information is needed for a stronger claim?

• a measurement only supports what it actually measures

• stronger conclusions may require more samples, repeated measurements, or information about the entire population.

how abiotic conditions such as temperature and moisture limit survival or establishment?

• abiotic factors are nonliving conditions.

• Temperature or moisture outside a species' tolerance range can prevent it from surviving or reproducing

how do predators, herbivores, competitors, parasites, or pathogens restrict a distribution (limit where a species can live)?

biotic factors (living organisms) can prevent a species from living in a specific area by making it harder to survive, reproduce, and access resources

unsuitable habitat vs. dispersal barrier

• Unsuitable habitat: conditions prevent the species from surviving

• Dispersal barrier: habitat could support the species, but the species cannot reach it.

how do habitat fragmentation and corridors change movement between suitable patches?

• fragmentation separates habitats and can make movement harder.

• a corridor connects habitat patches and can make movement easier

what evidence could be used to find why animals aren’t living in a unoccupied habitat?

• evidence about environmental conditions, predators/competitors, and whether the species can reach the area

• experiments or comparisons can help determine the cause

distinguish geographic range from the locations occupied during only one season?

• geographic range: the overall area where a species occurs

• a seasonal location may only be part of its range.

seasonal migration vs. dispersal between areas

• Migration: regular, often seasonal movement between areas

• Dispersal: movement of individuals away from where they were born or currently live

dispersal vs. dispersion

• dispersal = movement

• dispersion = how individuals are spaced out.

clumped vs. regular vs. random dispersion from spatial description

• clumped: individuals occur in groups

• regular: individuals are evenly spaced

• random: no predictable spacing pattern

how do uneven resources and shelter vs. competition and territorial behavior affect spacing?

• resources and shelter can cause clumping

• competition or territorial behavior can cause individuals to be more evenly spaced

when are quadrats appropriate? why should their placement represent the study area?

• Quadrats are useful for organisms that do not move much, such as plants

• They should be placed randomly or representatively so the sample reflects the whole area.

how does sampling along a line or measuring distance help survey a larger area or gradient?

• straight line through an area and record the organisms found along that line

• transect sampling

• they can show how abundance or distribution changes across a gradient or large area

steps in a mark-recapture study of a mobile population

• Capture and mark individuals.

• Release them.

• Allow them to mix back into the population.

• Capture another sample.

• Count how many are marked.

formula to use fraction of marked individuals in a second capture to estimate total population size

Population estimate = (number marked initially × number captured second time) ÷ number of marked recaptured

how does biased sampling distort an estimate? distinguish a relative index from an absolute estimate

• if the sample is not representative, the estimate can be too high or too low

• a relative index shows change or comparison, while an absolute estimate gives an estimate of the actual population size

use N(t + 1) = λ × N(t) for discrete breeding intervals; calculate and interpret lambda from successive counts

• N(t + 1) = λN(t)

• λ = N(t + 1) ÷ N(t)

• λ tells how the population changes each interval.

difference between constant proportional increase and adding a fixed number each interval

• Proportional increase: adds the same percentage each interval

• Fixed increase: adds the same number each interval

interpret positive, zero, and negative values of r for continuous population growth

r > 0: population increases.
r = 0: population stays stable.
r < 0: population decreases.

compare conditions and shapes associated with exponential and logistic growth

• exponential: unlimited resources → rapid J-shaped growth.

• logistic: resources become limited → S-shaped growth.

what is carrying capacity, K?

K = carrying capacity, the largest population the environment can support long-term.

how does growth change as a population approaches it or K changes?

• growth slows as the population approaches K

• if K increases, the environment can support more individuals.

density-dependent vs. density-independent

• Density-dependent: effect becomes stronger as population density increases
  Density-independent: affects populations regardless of density

use the evidence in a scenario to classify a limiting factor (do not rely on the factor name alone)

• ask whether the factor's effect changes with population density

• if it does → density-dependent. If not → density-independent

how does limited food or habitat can reduce growth as population density rises

• more individuals means more competition for limited resources, which can reduce survival and reproduction.

what do age-group patterns and an increasing doubling time suggest about human population growth?

• a population with many young individuals may continue growing

• an increasing doubling time means population growth is slowing

what does an ecological footprint measure?

measures how much land/resources are needed to support a person's or population's consumption and waste.

why can equal-sized populations have different footprints (amount of space a population occupies)?

equal-sized populations can have different footprints because resource use differs

intraspecific competition vs. interspecific competition

• intraspecific competition: competition within the same species

• interspecific competition: competition between different species

identify a shared limited resource and explain how competition can reduce success

• limiting resource is something needed for survival that is in limited supply, such as food, water, space, or light

• competition can reduce growth, survival, or reproduction.

how do competitors differ in their ability to obtain or use a limited resource?

• One species may be better at obtaining or using a resource, giving it a competitive advantage

conditions a species could use without limiting interactions from those it occupies with them

• fundamental niche: conditions/resources a species could use without competitors or other limiting interactions

• realized niche: what it actually uses when competitors and other interactions are present

organisms grown alone vs together (does competition affect occupancy?)

if a species does well alone but performs worse when another species is present, this suggests competition affects its ability to occupy that environment

how does heavy overlap in use of a limiting resource lead to competitive exclusion

• if two species depend heavily on the same limited resource, one may eventually prevent the other from surviving

• this is competitive exclusion

how does using different portions of a resource reduce competition and support coexistence?

Resource partitioning means species use different parts of a resource, allowing them to coexist with less competition

resource partitioning vs character displacement

• Resource partitioning: species currently use resources differently

• Character displacement: differences in traits evolve over generations because of competition

what measurements across places with and without a competitor suggest about character displacement?

• if traits differ more where competitors occur together than where they occur separately, this can provide evidence consistent with character displacement

why should you avoid assuming that coexistence means the species no longer compete at all?

Species can still compete and coexist if competition is reduced enough through resource partitioning or other mechanisms.

exploitation competition vs. interference competition

• exploitation competition: individuals compete indirectly by using up a shared resource

• interference competition: individuals directly prevent others from accessing a resource

what is chemical inhibition?

• allelopathy

• one organism releases chemicals that inhibit or harm another organism, often a competitor

what may happen when a predator or herbivore reduces a dominant competitor?

if dominant competitor decreases, another species may gain more resources and space, allowing its population to increase.

why would the same two competing species show different outcomes under different ecological conditions?

temperature, moisture, food availability, predators, and other conditions can change the strength of competition and which species has an advantage.

evaluate a claim by connecting proposed mechanism with evidence about resource use or species abundance

• look for evidence that the proposed mechanism actually occurs

• For example, if competition is claimed, check whether resources are limited and whether species perform worse when competing