Scales of Ecological Organization Biosphere Ecosystem Community Population Organism

Definition Population ecology is the study of births, deaths, and the dynamics forces which regulate the number of individuals in a population.

Density and Dispersion Is the number of individuals per unit area or volume Dispersion Is the pattern of spacing among individuals within the boundaries of the population

Population dispersion

Population dispersion spatial patterns spaced -- may indicate competing individuals clumped -- may indicate social patterns or resource distribution

A random dispersion Is one in which the position of each individual is independent of other individuals (c) Random. Dandelions grow from windblown seeds that land at random and later germinate.

A uniform dispersion Is one in which individuals are evenly distributed May be influenced by social interactions such as territoriality Figure 52.3b (b) Uniform. Birds nesting on small islands, such as these king penguins on South Georgia Island in the South Atlantic Ocean, often exhibit uniform spacing, maintained by aggressive interactions between neighbors.

A clumped dispersion Is one in which individuals aggregate in patches May be influenced by resource availability and behavior Figure 52.3a (a) Clumped. For many animals, such as these wolves, living in groups increases the effectiveness of hunting, spreads the work of protecting and caring for young, and helps exclude other individuals from their territory.

Density is the result of a dynamic interplay between processes Density is the result of a dynamic interplay between processes that add individuals to a population and those that remove individuals from it. Births and immigration add individuals to a population. Births Immigration PopuIation size Emigration Deaths Deaths and emigration remove individuals from a population.

The life table of Belding’s ground squirrels Reveals many things about this population

A survivorship curve Is a graphic way of representing the data in a life table… Figure 52.4 1000 100 10 1 Number of survivors (log scale) 2 4 6 8 Age (years) Males Females The survivorship curve for Belding’s ground squirrels Shows that the death rate is relatively constant

patterns in age structure Population patterns in age structure

r- vs K-selection r-selection K-selection r is the rate of a population’s increase K is a population’s carrying capacity Disturbance Common, irregular Rarer, more regular Mortality Variable, unpredictable Constant, predictable Competition Low or variable High, constant Pop. size Variable, below K Rel. constant, near K Consequence High r Good competitors

Small size Rapid growth Early reproduction Many, small offspring Large size Slow growth Late reproduction Few, large offspring

A. Body size and r On average, small organisms have higher rates of per capita increase and more variable populations than large organisms.

K vs. r selection: extremes in parental care Humpback whales Sea urchins

K vs. r selection: extremes

When there are no limits, populations grow faster, Population Growth Geometric growth vs. exponential growth vs logistic growth. Bottom line: When there are no limits, populations grow faster, and FASTER and FASTER! Invasive Cordgrass (Spartina) in Willapa Bay

The Simple Case: Geometric Growth Constant reproduction rate Non-overlapping generations (like annual plants, insects) Also, discrete breeding seasons (like birds, trees, bears) Suppose the initial population size is 1 individual. This indivual reproduces once & dies, leaving 2 offspring. How many if this continues?

Exponential Growth Assumes continuous breeding life history strategy and overlapping generations.

Human Population Growth www.smalltownproject.org/

What happens if there ARE limits? (And eventually there ALWAYS are!) Logistic Growth: The sigmoidal curve--carrying capacity (K) plays a role in determining population growth.

patterns in age structure Human population patterns in age structure

Exponential growth model

Exponential growth