Limits of Populations

Questions for today: What is Population Dynamics? What is Population Dynamics? How does Population Distribution affect Population Dynamics? How does Population Distribution affect Population Dynamics? What variables control Population Growth? What variables control Population Growth? What are the differences between Logistic Growth and Exponential Growth? What are the differences between Logistic Growth and Exponential Growth?

Population Dynamics There are four major characteristics used to describe populations: There are four major characteristics used to describe populations: –Distribution –Number –Age Structure –Density Population Dynamics is the study of how these characteristics change is response to environmental pressures. Population Dynamics is the study of how these characteristics change is response to environmental pressures.

Population Distribution Population Distribution is how individuals in populations are distributed or dispersed within a particular area or volume. Population Distribution is how individuals in populations are distributed or dispersed within a particular area or volume. Three patterns of Population Distribution: Three patterns of Population Distribution: –Clumping (most common) –Uniform –Random

Population Distribution Why populations Clump Why populations Clump 1.They clump where resources are available 2.Migrating individuals find resources easier. 3.Protection from Predators 4.Hunting is maximized 5.Reproduction is easier.

Population Growth There are four variables in Population Growth: There are four variables in Population Growth: –Immigration –Emigration –Births –Deaths The formula: The formula: Population Change = (Births + Immigration) – (Deaths + Emigration)

Populations Age Structure A population’s Age structure is defined as the proportions of individuals at various ages, and it can affect population growth. A population’s Age structure is defined as the proportions of individuals at various ages, and it can affect population growth. Three terms used to describe ages: Three terms used to describe ages: –Pre-reproductive (Population may Increase) –Reproductive (Population will Increase) –Postreproductive (Population will Decrease)

Exponential Vs. Logistic Growth Biotic Potential is the capacity for population growth under IDEAL conditions. Biotic Potential is the capacity for population growth under IDEAL conditions. Intrinsic Rate of Increase (r) is the rate at which the population of a species would grow if it had unlimited resources. Intrinsic Rate of Increase (r) is the rate at which the population of a species would grow if it had unlimited resources. –Individuals that have a high intrinsic rate: Reproduce early Reproduce early Short Generation Time Short Generation Time Reproduce Many Times Reproduce Many Times Many offspring in each generation Many offspring in each generation

Exponential vs. Logistic Growth No population can grow indefinitely No population can grow indefinitely –Limiting factors Environmental Resistance is the combination of all factors that act to limit the growth of a population. Environmental Resistance is the combination of all factors that act to limit the growth of a population. Biotic Potential + Environment Resistance = CARRYING CAPACITY

Exponential vs. Logistic Growth Carrying Capacity (K) is the maximum population of a given species that a particular habitat can sustain indefinitely without being degraded. Carrying Capacity (K) is the maximum population of a given species that a particular habitat can sustain indefinitely without being degraded. A population with few limitation can grow exponentially at a fixed rate of 1% or 2% per year. A population with few limitation can grow exponentially at a fixed rate of 1% or 2% per year. –Exponential growth starts slowly but then accelerates as the population increases. J-Shaped Curve J-Shaped Curve

Exponential Vs. Logistic Growth Logistic Growth involves rapid exponential growth followed by a steady decrease in population growth until the population size levels off. Logistic Growth involves rapid exponential growth followed by a steady decrease in population growth until the population size levels off. –Yields an S shaped or sygmoid curve Logistic Growth occurs because of environmental resistance. Logistic Growth occurs because of environmental resistance. –What happens if that resistance disappears.