POPULATION ECOLOGY

ECOLOGY

• Study of living organisms as groups

• Interactions between living organisms (predator-prey, parasitism etc)

• Interactions between organisms and their environments

• Study of patterns of distribution and abundance of organisms

Biotic factors

• Biotic factors: living organisms affecting others

• Producers, consumers, detrivores, decomposers, parasite, host, predator, competitor, herbivore, symbiont and pathogen.

Abiotic factors

• Non-living factors (chemical and physical)

• Temperature, light, soil, water, oxygen

Populations

• Groups of individuals of the same species living in the same geographic area

• Population ecologists study: distribution, density, rate of growth, demographics (old/young, male/female)

• Data and models used in population genetics and evolution

Communities

• All the populations in a given area

• Interactions and change over time are major focus of studies

• Ecological succession: Change in communities over time, especially after a natural or man made disruption

Primary succession

• Establishment and change in communities in a completely new environment

Secondary succession

• Occurs after a major disturbance ( fire, flood)

Ecosystem• An ecosystem (or ecological system) is a

collection of communities of organisms and the environment in which they live.

• Ecosystems can vary greatly in size. Some examples of small ecosystems are tidal pools or the stomach of an individual cow.

• Larger ecosystems might encompass lakes, agricultural fields, or stands of forests.

• Ecologists often invent boundaries for ecosystems.

Biomes• Groups of

ecosystems found in specific regions.

• Characteristics are usually determined by abiotic factors

Habitat

• Can be defined as the complete environmental requirements of an organism for survival: food, water, cover, space, and arrangement

Range• Geographical area where a population is

found

Niche

• The role of an organism in the community

• Specialists: can only survive in specific environments

• Eg: Koala, Panda bear

• Generalists: have large ranges because are not “fussy”

• Eg: rats, cockroaches and humans

Trophic structure

• Describes the feeding relationships in an ecosystem or community.

• Describes the abundance organisms in niches and the of flow of energy

Food webs

14.1: Characteristics of Populations

Population Density• Population Density (D)=total number of

individuals (N) divided by the area occupied by the population (A)

• Eg: If 480 moose live in a 600 hectare region of Algonquin park, then the population density is:

• D=N/A =480 moose/600 ha = 0.8 moose/ha

• Crude density: the number of individuals per unit of space or volume

• Ecological density: the number of individuals per unit of area or volume that is actually used by the individuals.

• Eg: the moose in Algonquin park do not use the open lakes. If the 600 ha of the park includes 70 ha of open lake then the ecological density would be 0.9 moose/ha.

(D=480 moose/ (600-70) ha

Patterns of dispersionClumped dispersion:

dense groups in parts of habitat best suited for survival

Uniform dispersion: even distribution

Random dispersion: habitat is uniform, little competition with other species

Measuring Populations

• Methods for estimating population sizes depend on the organism being studied (range, mobility)

• Populations are dynamic so scientists rely on sampling techniques to estimate the size of populations

• Some sampling techniques are direct (quadrant, tagging), other are indirect (number or tracks, nesting sites)

Quadrat sampling

• Quadrat sampling is usually carried out when the area under study is fairly uniform, very large, and or there is limited time available.

• Large numbers of samples are taken from different positions within the habitat.

• A quadrat frame is placed on the ground and the animals, and/ or plants inside it counted, measured, or collected, depending on what the survey is for.

• This is done many times at different points within the habitat to give a large number of different samples.

Mark- Recapture Method

• Used for wild animals• Marking techniques

are designed not to harm the individuals being caught

• Timing must be chosen carefully to ensure accuracy of numbers.

• Assumptions: – Every organism in a population has an equal

chance of being caught– During the time between initial marking and

recapture, the proportion of marked to unmarked remains constant

– Population size does not change (increase or decrease) during the study