Populations

Populations

• All individuals of a given species in a particular habitat

Communities

• All the organisms in a defined area• Ecosystem

– A community plus all the non-living (abiotic) components in a habitat

Populations

• Measuring Populations• How populations are regulated

Measuring Populations

• Population Density–Number of individuals per unit area

Population Density

• Influenced by

– Mortality– Emigration

– Natality– Immigration

Population Growth

• Population density fluctuates

• Natality + immigration = mortality + emigration

• Mortality is usually high

Types of Populations

• Open

– Natality, mortality, immigration and emigration affect population size

• Closed

– Only natality and mortality affect population size

Exponential Growth

• Under favourable conditions

• No predators, parasites or competition

Sigmoid Growth• Natural conditions• Curve flattens because

of– Competition– Predators– Parasites – Environmental resistance– Carrying capacity

Closed Population Growth

• No immigration or emigration

• Population slowly kills itself– Lack of

• Food• Space• Oxygen• Water

– Poisons itself

J Curve

• Closed population• Upper limit

– Seasonal conditions• Never reaches carrying capacity

Survivorship

• The chance of remaining alive to pass on your genes to the next generation

• Life expectancy

• Life span

Survival of the species

• Most energy is put into survival of species

Age Group structure

Population Distribution

• Clumped • Random• Evenly spread out

Clumped Populations

• Increases competition for food and space

• Reduces drying out• Greater defence• Easier to find mates• May also be due to

substrate

Evenly Spread

• Animals– By competition or

aggression– Defended territories– Limits population

density

• Plants– Shading– Competition– Allelopathy

Population Regulation

• Abiotic– Tolerance– Acclimation– Geographical Barriers – Liebig’s Law of Minimum

• Biotic– Predation, paracitism– Disease, toxic wastes– Competition, Humans

Tolerance

Acclimation

• When tolerance limits for an organism change they acclimatise– Slow process– Usually to seasons

Liebig’s Law

• The functioning of an organism in limited or controlled by whatever essential environmental factor is in the least favourable amount

Geographical Barriers

• Mountain ranges• Seas and oceans• Rivers

Predation

Humans

• Over-hunting– Extinction

• Destroy habitats– Draining swamps– Clearing forests

• Over-use of pesticides

• Toxic wastes