Population Ecology

Emergent characterisitics:

Density,

Age structure,

Sex ratio,

Demographics: birth rates, death rates, immi-, emigration

Evolution

Unitary and Modular populations;

solitary individuals vs. clones/modules

In genetic terms:

individuals arise via sexual reproduction: Genets

microbes?

Vegetative growth: Ramets = clones

Aspen, Oaks, sponges, coelenterates (corals, hydroids)

Spruce Grasses-

adaptation to gemination difficulty:

stress environments, competition

Ramets are horizontal modules (Fig 10.2; Aspen)

Modular growth can also be verticle: coral polyps, parts plants

respond as individuals in a population

(growth & death later)

Metapopulations Fig. 10.3

Subpopulations

separated by habitat fragments/breeding sturctures

Terrestrial amphibians

Gene pool continuity maintained by immigration:

1 individual per generation exchange

Gene Pool: total genetic information of the species

Individuals only carry part.

Interbreeding- Gene Flow, immigration, emigration

Change in gene pool with time = evolution

Density

Crude density: by census- individuals per unit space

Assumes all space equal, homogeneous environment

Ecological Density: individuals per “habitatable space”

Difficult to measure

Spatial Distribution patterns; Fig. 10.4

Uniform/even, Random, Clumped

Random is rare:

uniform habitats, constant resources, no interactions

intertidal inverts fiddler crabs

inverts in forest floor

some trees

Uniform/Even/Regular: more even than by chance

Intraspecific Competition: territoriality

Fig 10.5 golden eagles

Plant competition

Clumped/Aggregated

Distibution of abiotic conditions of the environment

Reproductive structures

Ramet/Vegetative growth of plants

Social interactions

Scale Dependence (spatial & temporal):

All three patterns may be observed for a single species

Pines, fish, flocks

Social Behavior: benefits must overcome the costs of density

Predator protection

Improved foraging

Modification of environment

Predator protection:

Mutual vigilence, sometimes with division of labor

Confusion, physical defense, geometirc effects

Predator attack is on indivivdual, group attack fails

Improved Foraging: mutual vigilence, information transfer,

For predators: cooperative hunting, protecting a kill

Modifying the environment:

Humans, bacteria, Eusocial organisms: bees

Temporal Dispersion Patterns

Cyclic Behaviors:

Activity patterns, energy resources (flower blooming),

plankton migrations, tidal rythyms, etc.

Non-migration dispersal: immigration, emigration, no return

Dispersal of offspring/seeds

tends to be a logrythmic function of distance

Animal exceptions Fig 10.8

Migration patterns: return Fig. 10.9

Seasonal escape of abiotic factors, energy reosurces, breeding

Often combination of factors

Age Structure

Prereproductive, Reproductive, Postreproductive

Stable Age Distribution: population may grow or decline,

but age structure remains the same

Stationary age distribution: population is stable,

but not growing or declining

Determining the age of organisms often difficult:

size not always corelated Fig. 10.12

Deer jaws, Tree rings, Oyster hinges, Otoliths

Plants: seed banks and supressed growth

Sex ratios

Most sexually reporducing organisms produce 1:1 ratios offspring

Sex determined by Temp, Female Behavior, Genetics

Some change: hemaphrodites: protandrous-oyster

Mammals tend to have higher male:female ratios at birth

Lower male:female ratios with age:

Birds tend towards higher male:female ratio with age

Sex specifc survival differences