3.2.2 - Population Ecology Flashcards
what is a limiting factor?
- a limiting factor is an abiotic or biotic factor that restricts the number of individual in a population
what are the types of biotic limiting factors?
- competition for resources
- predation
- disease
why does competition occur?
- when organisms struggle to survive in a habitat with limited resources
why does predation occur?
- the predator-prey relationship is a balance between the two populations
- as the prey population increases, the predator population increases
- as the prey population decreases, then so does the predator population
why does disease occur?
- diseases and parasites can be dependent on population size
- larger population = more parasites and disease = limits how
what are the limiting abiotic factors?
- space
- availability of nutrients
- pollution
- natural disasters
- extreme climatic events (drought, cyclones etc)
what factors are biotic and density dependent?
- predation
- competition
- disease
what factors are abiotic and density dependent?
- space
- availability of nutrients
recall the biotic and density independent factors
none
recall the abiotic and density dependent factors
- pollution
- natural disasters
- extreme climatic events
what is carrying capacity?
- because of the limiting factors, each ecosystem has a finite capacity for growth connected to its carrying capacity
- the size of the population that can be supported indefinitely on the available resources and services of that ecosystem
- different for every species
how do you explain carrying capacity graphs?
- when a population is below its carrying capacity, it will increase in size
- birth rate exceeds death rates
- when a population is above its carrying capacity, it will decrease in size
- death rate exceeds birth rates
what factors determine population size?
- births
- deaths
- immigration
- emigration
how do you calculate population growth?
- population depends on the number of individuals added to the population from births and immigration, minus the number lost through death and emigration
how do you calculate percentage change of a population?
- if the result is positive, it is an increase
- if the result is negative, it is a decrease
how do you calculate population size?
- collect a sample of individuals
- after a period of time, collect more individuals from the area and count the number that have been marked
- we assume that a sample, if random, will contain the same proportion of marked individuals as the population does
how do you read population growth graphs?
two types of population growth patterns may occur depending on specific environmental conditions
- an exponential growth pattern (J curve) occurs in an ideal, unlimited environment
- a logistic growth patterns (S curve) occurs when environmental pressures slow the rate of growth
describe exponential growth (J-curve)
- exponential population growth will occur in an ideal environmental where resources are unlimited
- in such an environment, there will be no competition to place limits on the rate of growth
- initially population growth will be slow as there is a shortage of reproducing individuals that may be widely dispersed
- as population numbers increase the rate of growth similarly increases, resulting in an exponential (J-shaped) curve
- exponential growth can be seen in populations that are very small or in regions that are newly colonized by a species
describe logistic growth (S-curve)
- logistic population growth will occur when population numbers begin to approach a finite carrying capacity
- the carrying capacity is the maximum number of a species that can be sustainably supported by the environment
- as a population approaches the carrying capacity, environmental resistance occurs, slowing the rate of growth
- this results in an S-shaped growth curve that plateaus at the carrying capacity (denoted by k)
- logistic growth will eventually be seen in any stable population occupying a fixed geographic space
