Chapter 53: Population Ecology Flashcards
What is a population?
A group of individuals of the same species that occupy the same general area
What 4 factors influence population?
Density
Dispersion
Structure
Growth Rate
What is density?
The number of individuals per unit area or volume
- density is the result of an interplay between processes that add individuals to a population and those that remove individuals
What is dispersion?
The pattern of spacing among individuals within the boundaries of the population
______ and ______ affect population size.
Births; deaths
What are the 3 types of dispersion?
- Clumped dispersion
- Uniform dispersion
- Random dispersion
What is clumped dispersion?
When organisms aggregate (group) in patches
- this is due to resource availability and behavior
What is uniform dispersion?
When organisms are evenly distributed
- this is due to social interactions such as territoriality (claiming territory)
What is random dispersion?
When the position of each organism is independent of other organisms
- this is due to the absence of strong attractions or repulsions
What is demography?
The study of vital statistics of a population and how they change over time
What factors affect demography?
- Population size
- Density and Distribution
- Age Structure, Sex Ratio
- Birth, Death, Immigration and Emigration
What is age structure?
The relative number of individuals at each age
What is immigration?
The influx of new individuals from other areas
What is emigration?
The movement of individuals out of a population
What is a life table?
An age specific summary of the survival pattern of a population
What is the best way to construct a life table?
Follow the fate of a cohort, a group of individuals of the same age.
What is a Type I species?
Species that invest a lot of energy into caring for their young
- have low death rates early in life
E.g., humans and large vertebrates
What is a Type II species?
Species that have an equal probability of dying at any age
E.g., mammals and birds
What is a Type III species?
Species that invest little energy raising their young
- high death rages among offspring
E.g., fish, invertebrates, plants
What are the 3 types of population growth models?
- Constant Growth
- Exponential Growth
- Logistic Growth
What is constant growth?
When the population continues to grow constantly
What is exponential growth?
The increase of a population in an ideal, unlimited environment.
Equation:
^N/^t = rN
^N = change in population size ^t = change in time If r>0 = increasing population If r<0 = decreasing population N = current population size
What is the intrinsic rate of increase (r)?
The rate at which the population increases
What is per capita rate of increase?
A population’s growth rate, which equals the birth rate minus the death rate.
^N/^t = B - D
^N = change in population size ^t = change in time
What is expected of exponential growth?
It cannot continue on forever.
It has a ‘Carrying Capacity’ (K) (limit).
Either:
- the population will crash
- slower population growth
What is the J-shaped curve?
An exponentially growing population that is rebounding after being reduced.
What is logistic growth?
A population’s change over time in response to feedback from the environment or its own population density. (S curve!)
Equation:
dN/dt = rN (K-N)/K
dN = rate of change in population size dt = rate of change in time If r>0 = increasing population If r<0 = decreasing population N = current population size K = carrying capacity
What are density-dependent factors?
Factors that cause a change in the population size that are related to the population density.
E.g., if you have a small density of 20 birds in a large forest, their population will continue to increase because they have plenty of resources. However, if you have a large density of 6,000 birds in a smaller forest, the birds will compete for their resources and the population may start to decline.
What are density-independent factors?
Factors that cause a change in the population size that are unrelated to the population density.
E.g., if you have a population of 20 deer, or 50 deer, or 100 deer, and there’s a fire, it doesn’t matter how many deer you started with, what matters is that the population got affected regardless of how many there were.
The effects of density-dependent factors _________ as the population density ______.
Increases; rises
What is life history?
The events of an organism from conception to death.
- it’s main focus is the adaptations that influence reproductive success
How many humans can the earth support?
What is the carrying capacity of humans?
Average estimate is 10-15 billion
What is the ecological footprint?
The aggregate (total) land and water area needed to sustain the people of a nation
- how to measure our carrying capacity
Which growth model explains human population growth?
Exponential
- slowly increased in 1650
No longer growing exponentially, but still increasing
Life histories fall into two patterns shaped by natural selection.
a) Opportunistic species (r-selected)
b) Equilibrium species (K-selected)
Explain the differences between these two.
a) These organisms are short-lived, reproduce at an early age and have many offspring and provide little care.
- e.g., insects
b) These organisms are long-lived, reproduce later in life and provide extensive parental care.
- e.g., birds, large mammals
