Ecology Exam 3

growth rate

the number of new individuals produced in a given amount of time minus the number of individuals that die

intrinsic growth rate (r)

the highest possible per capita growth rate for a population under ideal conditions (abundant resources and mates)

r > 0

population grows

r = 0

population stays constant

r < 0

population declines

exponential growth model N_t = N₀e^rt

the population grows at a continuous rate, occurs under ideal conditions (no competition), J-shaped curve

geometric growth model N_t = N₀ λ^t

the population increases at regular time intervals (e.g. species that reproduce only during part of the year)

λ

greek letter “lambda” which is the growth factor per time interval

λ > 1

population grows

λ = 1

population stays constant

λ < 1

population declines

logistic growth model dN/dt = rN(1 - N/K)

incorporates the carrying capacity (k), describes slowing growth of populations at high densities, S shaped curve (sigmoidal curve)

K

the maximum population size that can be supported by the environment long term

inflection point

the point on a sigmoidal growth curve at which the population achieves its highest growth rate (N = K/2)

density-independent factors

abiotic factors (natural disasters, extreme weather, droughts) that limit population size regardless of the population density

density-dependent factors

biotic factors whose effects intensify as population density increases

negative density dependence

the rate of population growth decreases as population density increases (e.g. competition for resources, predation, disease)

positive density dependence (allee effect)

the rate of population growth increases as population density increases in very small populations (e.g. easier to find mates)

age structure

the proportion of individuals that occurs in different age classes. a pyramid with a broad base indicates a growing populations

type I survivorship curve

high survival in early and middle life, then rapid decline in older age (e.g. humans, large mammals)

type II survivorship curve

Constant mortality rate throughout life (e.g., some birds, rodents)

type III survivorship curve

High mortality early in life, with few individuals surviving to adulthood (e.g., many fish, plants)

life tables

summarizes survival and reproductive rates of a population at different ages

cohort life table

Follows a group of individuals born at the same time throughout their lives to record survival and death rates

static life table

Records survival data of individuals of different ages at one point in time, rather than following a cohort

predator

• An organism that kills and consumes other organisms (prey) for food.

• Usually kills prey immediately (e.g., lions hunting zebras)

parasitoid

• An organism (often an insect) that lays its eggs on or in a host; the developing larvae eventually kill the host.

• Combines parasitism and predation (e.g., certain wasps laying eggs inside caterpillars).

parasite

• An organism that lives on or inside a host, feeding on it but usually not killing it immediately.

• Often weakens the host over time (e.g., ticks on mammals, tapeworms in intestines).

herbivore

• An organism that feeds on plants or algae.

• Can affect plant populations by consuming leaves, stems, roots, or seeds (e.g., deer, caterpillars, rabbits).

predator-prey dynamics

populations of predators and prey fluctuate in synchronized cycles, with predators lagging behind prey

prey equation

dN/dt = rN - cNP

predator equation

dP/dt = acNP - mP

prey isocline

The population size of prey at which its growth rate is zero (births = deaths).

predator isocline

The population size of predators at which their growth rate is zero.

join equilibrium point

The point where prey and predator isoclines cross; both populations have zero growth, indicating a stable balance.

biological control

The use of natural predators, parasites, or pathogens to manage pest populations sustainably.

competition

A negative interaction (-/-) where individuals or species vie for the same limiting resources

resource

• Anything consumed or used that increases population growth (e.g., food, water, space, nutrients).

• Abiotic factors like temperature are not considered resources.

liebig’s law of the minimum

Population growth is limited by the scarcest resource, even if others are abundant.

intraspecific competition

Competition among individuals of the same species

interspecfic competition

Competition between different species

competitive exclusion principle (gause)

two species competing for the exact same resources cannot stably coexist; one will outcompete the other

character displacement

Evolutionary changes in species traits that reduce competition when species coexist

closely related species competition across taxa

Often compete more intensely due to similar resource needs

distantly related species competition across taxa

May compete less directly but still affect each other’s populations.

factors altering competition

Abiotic conditions, disturbances, herbivory, predation, and climate change can prevent one species from dominating

lotka-volterra competition models

Mathematical models extending logistic growth to include competition effects.

competition coefficients

Parameters that measure the impact of one species on the growth of another.

community

A group of interacting species living in the same area

ecotone

A transition zone between two different communities or ecosystems

zonation

the spatial pattern of species or communities in distinct zones

species richness

The total number of species in a community

relative abundance

Proportion of individuals of a species relative to the whole community.

absolute abundance

Total number of individuals of a species

rank-abundance curves

Graphs showing species ranked by abundance to visualize richness and evenness

diversity indices

Combine richness and evenness into a single value

shannon’s index

Measures uncertainty in predicting species identity; higher values mean more diversity.

simpson’s index

Measures the probability that two randomly selected individuals belong to the same species; lower values indicate higher diversity

producers

Autotrophs that make their own food through photosynthesis or chemosynthesis.

consumers

organisms that eat other organisms

primary consumers

herbivores

secondary consumers

carnivores that eat herbivores

tertiary consumers

carnivores that eat other carnivores

indirect effect

Interaction between two species mediated through a third species

trophic cascade

Indirect effects in a food web initiated by a predator that affect multiple lower trophic levels

top-down control

When predators regulate the abundance of prey and lower trophic levels

bottom-up control

When the availability of resources (nutrients, plants) controls the structure of the ecosystem