APES Unit 3

limiting resource

something that a population cannot live without and that typically occurs in quantities lower than the population would require to increase in size

carrying capacity

the limit of how many individuals in a population the environment sustain; often denoted as K

Population size (N)

the total number of individuals within a defined area in a given time

Population Density 

number of individuals per unit area

Population disruption

how individuals are distributed with respect to one another

Population Sex Ratio 

the ratio between males and females

Population age structure

how many individuals fit into particular age cohorts

Niche Generalist

can live under a very wide range of abiotic or biotic conditions (ex. Raccoons) 

Niche Specialists 

live under a very narrow wide range of conditions (ex. Panda)

2 main reproductive patterns

K selected and R selected

K selected species

species that have a low growth rate, which causes the population to increase slowly; population fluctuations are small.

R selected species

species that have a high growth rare condition which can lead to population booms and die- offs (ex. bunnies, cockroaches)

Survivorship  curves 

A graph showing the proportion of individuals surviving to each age in a given species or population 

x axis

age or time

y axis

number of survivors

Type 1

High survival rates throughout most of their lives, but then individuals die off. (K-selected species like humans, whales, elephants)

Type 2

Constant decline in survivorship throughout their lives (squirrels, corals)

Type 3

Low survivorship at a younger age with few reaching adulthood (R-selected species like mice, weeds, frogs, fungi)

Population growth rate

the number of offspring an individual can produce in a given time period, minus the deaths of the individual or its offspring during the same period

Intrinsic growth rate ( r )

the growth rate of a population under ideal conditions 

Oscillation 

up and down movement 

Density Dependent

influence an individual’s probability of survival and reproduction in a manner that depends on the size of the population (ex. Food available, cometition, predation)

Density Independent

Have the same effect on an individual’s probability of survival and amount of reproduction at any population size (ex. weather, natural disasters, human activities)

Exponential Growth Model

when populations are not limited by resources, their growth can be very rapid. Also illustrates density independent growth pattern. (J shaped curve)

Logistic Growth Model

Initial growth is exponential but slows as the population approaches the carrying capacity of the environment (K). Density Dependent type of growth. (S shaped curve)