Unit 8: Topic 3 - Population Ecology Flashcards
What is a population?
Population is a group of individuals of the same species living in an area. They interact with each other and with the environment.
Ex: A flock of blackbirds is a population, considering that they are of the same species.
What is population ecology?
Population ecology analyzes factors that affect population size and why the size changes through time.
What causes population to fluctuate?
Birth rate and death rate affect population.
Population trends:
Growth: Birth rate > Death rate
Decline: Birth rate < Death rate
Steady: Death rate = Birth rate
What are population dynamics?
A population’s growth/decline over time is called population dynamics.
What categories of factors affect population growth/decline?
Density-dependent and density-independent factors affect population growth/decline.
What is a density-dependent factor? Provide examples.
A density-dependent factor is an increase in death rate or decrease in birth rate due to higher population density (number of individuals per unit of area).
Examples: Limits how much a population can grow bases on its density.
Competition- If many individuals are residing in an area (high population density), there with be fewer resources for each of them to share. This will cause competition between populations for resources (an element of natural selection).
Predation- If there is a surplus of a population, many predators with prey on them for food.
Waste & Disease- Within a high population density, there will be more waste the population releases. High waste levels subject the population to disease spreading in the environment. Also, there is a greater chance of spreading the disease from individual to individual.
Territoriality- Less space but more individuals hint at smaller territories and conflict/competition due to spacing issues.
What is a density-independent factor? Provide examples.
A density-independent factor is an increase in death rate or decrease in birth rate due to causes other than change in population density.
Examples:
Natural disaster- This an event that occurs in the environment naturally and doesn’t relate to population density, but it has the power to control the density.
Drought- This an event that occurs in the environment naturally and doesn’t relate to population density, but it has the power to control the density.
How can you determine the growth rate of a population?
Population Growth:
dN/dt = B - D
dt = change in time
B = birth rate
D = death rate
N = population size
Example: Population of 500 individuals, 40 are born per year, 20 die every year.
dN/dt = B - D
dN/dt = (40) - (20)
dN/dt = 20 individuals/year
Analysis: The growth rate of this population is 20 individuals every year.
How can you determine the per capita growth rate/intrinsic rate of increase of a population?
Per capita growth rate:
dN/dt = rN, solve for r
or r = (dN/dt) / N
r = per capita growth rate/intrinsic rate of increase (how quickly population grows per individual)
N = population size
Example: Population of 500 individuals, 40 are born per year, 20 die every year.
r = (dN/dt) / N
r = (20) / (500)
r = 0.04
Analysis: The intrinsic rate of increase is very low, so the population isn’t growing much every year.
What is exponential growth?
Exponential growth is when a population reproduces without limits/constraints.
The population grows by a constant proportion at each instant in time.
During a period of exponential growth, there is an abundance of space and resources and no density-dependent/density-independent limiting factors.
How can you determine exponential growth of a population?
dN/dt = (r)max(N)
dt = change in time
N = population size
rmax = maximum per capita growth rate of population
Ex: Which population will grow faster?
- dN/dt = 1.0N
OR - dN/dt = 0.5N
The (r)max of population 1 is 1.0 while the (r)max for population 2 is 0.5 and we know that 1.0 > 0.5. If given that the value of N, the population size, will be the same for both populations, population 1 will exponentially grow faster because it has a greater (r)max or maximum per capita growth rate of a population.
