POPULATION

Definition

• Populations are groups of individuals of the same kind occupying a particular place at a particular time

POPULATIONS

Problems with Definition

• Definition of boundaries (often arbitarily set by ecologists)
• Defining the individual (not a major problem for animals)

POPULATIONS

HUMAN DEMOGRAPHIC Definition

POPULATIONS

GENETICS Definition

POPULATIONS

POPULATION ECOLOGY Definition

Genetic Growth vs. Modular Growth

• Example: In plants, individuals commonly produced by sexual reproduction (but not always)
• Genets: genetic, evolutionary units (arise from sexual reproduction
• Ramets: clones, or modular units arising from parental material
• Also some animals (ex: coral reefs)

SPATIAL SCALES

• Local populations can occupy very small habitat patches like a puddle
• Metapopulation: A set of local populations connected by dispersing individuals
• Populations can be considered at a scale of regions, islands, continents, or seas
• Entire species can be viewed as a population

POPULATION STABILITY

• Populations differ in their stability, Some stable for thousands of years
• Other populations persist only because of continuous immigration from other areas
• On small islands, populations often get extinct, but then these islands can be recolonized
• Temporary populations: consist of organisms at a particular stage in life cycle

POPULATION ECOLOGY

Major Problem 

POPULATION ECOLOGY

Main Axiom

• Organisms in a population are ecologically equivalent

POPULATION ECOLOGY

Ecological equivalency

1. Organisms undergo the same life-cycle
2. Organisms in a particular stage of the life-cycle are involved in the same set of ecological processes
3. Rates of these processes (or probabilities of ecological events) are basically the same if organisms are put into same environment (some individual variation may be allowed)

Models as Analytical Tools

• 2 important processes in model devlopment
• Abstraction (generalization): taking the most important components of real systems and ignoring less important components
• Interpretation: means that model components (parameters, variables) and model behavior can be related to components, characteristics, and behavior of real systems

 MODELING STRATEGY

• Select optimal level of complexity
• Never plan model development for more than 1 year
• Avoid the temptation to incorporate all available info into model
• Follow specific objects, don't try to make universal model
• If possible, incorporate already existing models

POPULATION SYSTEM

Major components

• Population itself: organisms in population can be subdivided into groups according to age, stage, sex, etc.
• Resources: food, shelters, nesting places, space
• Enemies: predators, parasites, pathogens
• Environment: air (water, soil) temp, composition
• Variability of characteristics in time and space

Population Distribution

• Individuals of a species will occupy any are that:
• Can be reached
• Satisfies its habitat requirements
• Is not inhabited because of competition, predation, or disease

POPULATION DENSITY

• Density: size of a population in relation to a defined unit of space
• Crude density: measure of number of individuals per unit area
• Ecological density: density measure in terms of the amount of area actually available as living space

POPULATION DISPERSIONS

Spatial dispersion

• Arrangement of individuals in space

POPULATION DISPERSIONS

Spatial dispersion

Clumped

• Results from heterogeneous/nonrandom habitat and resource distribution
• Most common pattern

POPULATION DISPERSIONS

Spatial dispersion

Uniform

• Resources equally distributed throughout
• Results from intraspecific competition among individuals (territoriality)

POPULATION DISPERSIONS

Spatial dispersion

Random

• Individual distribution independent of others
• Least common

POPULATION DISPERSIONS

Temporal Disperson

• Distribution patterns based on time
• Daily changes in light/dark, seasons, tidal cycles

POPULATION DISPERSIONS

Dispersal

• Movement of individuals from home site
• May result from special life history stage (seed)
• May be result of insufficient resources, deteriorating habitats, and alleviation of inbreeding

POPULATION DISPERSIONS

 Philopatry

• Site tenacity
• Young tend to move from where they were hatched or born but stay in the same general area
• Adults tend to return to same breeding site every year

POPULATION DISPERSION

Vagility

• Ability to disperse
• Increased dispersal ability through adaptive mechanisms

POPULATION DISPERSIONS

Viscous Species

• Low vagility > little gene flow
• Ecotypes: subspeciation, characterized by habitat