Population Ecology

Biology 11

Ecology

• The study of the relationships the living organisms have with each other and their environment.

• Dependant on interactions between organisms, as well as between individuals and their environment.

Symbiotic relationships

• Symbiosis (meaning “living together”) is a direct interaction between two species where at least one of the two species benefits from the association.

• The host is the larger of the two species and the more independent in the symbiotic relationship.

Types of symbiotic relationships

• Parasitism is a type of symbiotic relationship in which one organism (the parasite) benefits at the expense of the other organism (the host) (+/- relationship).

The tick receives the blood it needs to live, but the dog is damaged by the ticks transmitting disease in its blood.

Types of symbiotic relationships

• Mutualism is a type of symbiotic relationship in which both organisms benefit and neither are harmed (+/+ relationship)

Ex: Bees & flowers

Types of symbiotic relationships

• Commensalism is a type of symbiotic relationship in which one organism benefits and the other organism is unaffected (+/0 relationship).

Ex: Clownfish and sea anemone

A habitat is a place or region having a particular combination of biotic and abiotic characteristics. Organisms adapt to the habitats within which they usually live.

• Ex: The taiga (Boreal forest) biome covers a large part of central and northern Canada, Europe and Asia. From the North to the South and from the East to the West, the taiga varies greatly in density and type of tree. Also, each biome can contain an assortment of different habitats. Each habitat contains its own combination of organisms and abiotic conditions.

The study of ecology happens at many levels, from individual organisms to populations, from communities to ecosystems.

• A population is a group of

individuals of the same species (organisms that resemble one another in appearance, behaviour, chemistry and genetic makeup) who occupy the same geographical region.

Demography: the study of populations.

• Regarding the size, density age structure and growth of populations.

• The density of a population corresponds with the number of individuals per unit of volume or surface area.

• Dispersion indicates how individuals of a population are spread within the geographical limits (uniform or in compact masses).

Population dispersion

• The general pattern in which individuals are distributed through a specific area.

Demographic growth

• Births and immigration increase a population. On the contrary, deaths and emigration reduce a population.

The size of a population is affected by the following 4 factors:

• Birth rate: The number of new individuals in a population due to reproduction.

• Mortality rate: The number of deaths within a population.

• Immigration: The number of individuals arriving in a new region.

• Emigration: The number of individuals leaving the population.

• Changes in the size of the population:

Variation The number The number

in the size of births of deaths

of a population = within - within

in a given this interval this interval

period of time of time of time

The growth rate is the number of births or immigration minus the number of deaths or emigration in a given time period.

IF:• Birth rate + immigration > mortality rate + emigration,

the population is increasing.

• Birth rate + immigration < mortality rate + emigration, the population is decreasing.

• Birth rate + immigration = mortality rate + emigration, the population is unchanging.

Population growth

• Population growth can be represented by the following model:

• A: Exponential growth phase (logarithmic): The phase in which the number of individuals increases rapidly (exponentially).

• B: Transitional growth phase: The phase in which the growth rate slows considerably – the population continues to increase, but at a much slower rate.

• C: Stationary phase (Plateau phase): The phase in which the number of individuals has stabilized and there is not more growth (carrying capacity).

Causes of the exponential phase:• Abundant resources• Little competition between habitants• Favourable abiotic factors (temperature, oxygen levels, etc.)• Little predation or illness

Causes of the transitional phase:• There is an increase in competition for resources • There is an increase in predation• Illness starts to spread due to demographic growth

Causes of the stationary phase:• Less space• Limited food resources (consequently, there is a decrease in birth rate)• There are more predators• Easier for illness to spread

Population pyramids• A graph that shows the distribution of various age groups in a

population (typically that of a country or region of the world), which forms the shape of a pyramid when the population is growing.

• Used in Ecology to determine the overall age distribution of a population; an indication of the reproductive capabilities and likelihood of the continuation of a species.

Carrying capacity

• The maximum population of a species that a given environment can support.

• Seychelles Paradise Flycatcher need approx an acre of mixed forest per couple. They live on a small island in North-East Madagascar.

http://www.rareconservation.org/blog/index.php?paged=2

4 factors that determine carrying capacity

1) Energy and matter• Limited by the quantity of

light energy. • Limited by the quantity of

water, carbon and other materials.

http://www.condorjourneys-adventures.com/costarica_nature.asp

http://weathersavvy.com/Q-Climate_DesertsHot.html

4 factors that determine carrying capacity

2) Food chains• Limited by the quantity of

available food (lowest tropic level)

• Limited by predators (highest tropic level)

http://www.intarttiles.com/robertekennedy.htm

4 factors that determine carrying capacity

3) Competition• Competition for food, water,

sexual partners and space.

• Intraspecific Competition:

between individuals of the same species.

• Interspecific Competition: between different species.

http://www.maxi-fond-ecran.com/fond-ecran-photo-paon/paon/telecharger-fond-ecran-photo-paon-p18507.html

http://www.tnstate.edu/ganter/B412%20Lab2%20PlantComp.html

http://www.allposters.com/-st/Elephant-Posters_c646_p3_.htm

4 factors that determine carrying capacity

4) Population density• The number of individuals

who can live in a region at the same time.

http://reliableanswers.com/images/wallpaper/penguin_party.jpg

http://www.naturetrek.co.uk/wildlife-holidays/wildlife-holidays.asp?ID=3

Density dependent factors

• When the density surpasses biotic capacity, we call it overpopulation.

• Overpopulation can: • Increase stress and the

propagation of illness and parasites.

• Increase aggression and negligence of babies.

• When this happens, the population will decrease.

• Other density-dependent factors include: disease, reproductive rates, predator/prey relationships, competition, availability of mates, etc. http://www.envirowarrior.com/animal-

abusers-the-worst-polluters/

Density independent factors

Limits the population regardless of its size.

-Forest fire

-Earthquake

-Volcanic eruption

-Tornado

http://tiee.ecoed.net/vol/v3/issues/frontier_sets/yellowstone/sci_teaching.html