Population ecology

Geographic distribution/ range Population density Population dispersion Immigration Emigration Logistic growth

Exponential growth Biotic potential Environmental resistance Carrying capacity Density-dependent factors Density independent factors

1. Geographic distribution2. Density3. Dispersion4. Growth rate5. Age structure

What is a population?What is a population?A population is a group of individuals of the same species occupying the same general area.

- geographical range of a species or a group of species

- the suitability of habitats influences the distribution of a species (each species is adapted to a rather limited range of abiotic and biotic conditions)

Population densityPopulation density

- the number of individuals per unit area or volume

- pattern of spacing among individuals in a habitat

Types of dispersion:RANDOM

- habitat conditions are uniform / resource availability is steady- individuals neither attract nor avoid each other- rare in nature

UNIFORM- individuals are evenly spaced in a habitat- due to competition or territorial behavior

CLUMPED- species are aggregated in patches- most common in nature because:

cluster around patchy resources live in social groups species has limited dispersal powers

- increase in the size of a population of organisms

population size the number of individuals that contribute to a population’s gene pool

For mobile animals Individuals are captured and marked in some way,

then the marked animals are released. Later, animals are captured and checked for marks. In the later sample, the proportion of marked

individuals should be representative of the proportion marked in the whole population.

- increase in the size of a population of organisms

population size the number of individuals that contribute to a population’s gene pool

Factors that affect population size:1. Number of births (natality)2. Number of deaths (mortality)3. Immigration/Emigration

Immigration – the arrival of new residents from other areasEmigration - individuals permanently move out of the

population

–no overall increase or decrease during a specified interval; population size is stabilized (assuming that immigration and emigration balance each other number of births = number of deaths)

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Individuals in population have constant rate of reproduction

Over time, becomes infinitely large Under ideal conditions with unlimited

resources, population will grow exponentially Ideal condition- abundant space, food,

protection against predator and disease

Does not continue naturally for a long time

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Carrying capacity

Due to decrease in resources that lead to decrease in population growth

Decrease in pop growth maybe caused by decrease in death rate, increase in death rate or the occurrence of both at the same time at the same rate Is also true for emigration and immigration

Recall: limiting factors determine the primary productivity of an area

In population, a limiting factor causes population growth to decrease

Pop size

competition

predation

Parasitism and disease

Drought and other climate extremes

Human disturbances

Depends on the population size Is due to population density

Major force of evolution Competition should be decreased Evolution will lead separation of niches

No same species can occupy the same niche at any given place and time

One of the best population control Characterized by fluctuations of the prey and

predator populations

Limiting factor that affects the population regardless of its size Characterized by a CRASH in the population

size

biotic potential/reproduction potentialmaximum rate of growth of a population

conditions are optimal / idealhigh reproduction, low mortality

environmental resistancefactors that limit population growth

limiting factors: food, space, O2, shelter, accumulation of wastes

carrying capacity maximum number of individuals in a population (or

species) that a given environment can support indefinitely

in the steady state (of logistic growth) size oscillates around this number

Age structure the number of individuals in each of several

age categories:1. prereproductive age – have the potential to

produce offspring when they mature2. reproductive age – actual reproducing

members3. postreproductive age 1 & 2 make up the population’s

reproductive base  

The biotic potential of an ecosystem is affected by environmental resistance, thus resulting in a maximum carrying capacity

Understanding patterns in human population growth is important in addressing population problems around the world.