4.1 Population Characteristics

Define Species

group of organisms which have ability to interbreed, under natural conditions, to produce fertile offspring

Define Population

group of organisms of same species that are living in same area at same time

Define Habitat

place where species normally lives

Define Niche

role or function of species within an ecological community

Define Community

all populations in a given ecosystem at a given time

Define Ecosystem

living (biotic) and non-living (abiotic) components that function as a unit in a given area or volume

Define Population Density

number of individuals of species per unit area or volume

Define Crude Density

number of individuals per total area

Define Ecological Density

number of individuals per unit area that is actually used

Tell me about Population Dispersion? What are the types of Population Dispersion?

Since resources are not always evenly distributed throughout environments, all populations do not show the same pattern of dispersion

1. Clumped

2. Random

3. Uniform

Tell me about Clumped Populations

most populations show this pattern

Examples: birds “flock”, fish “school”, zebra “herd”, mushrooms on rotted logs

Tell me about Random Populations

when resources are evenly distributed and there is little interaction between individuals

Examples: trees in tropical rain forest (very rare)

Tell me about Uniform Populations

individuals are equally spaced apart (almost never seen in nature, but this is how crops are planted)

Examples: due to strong competition for nest sites, King penguins show this pattern

What are the ways to count populations?

1. Quadrats

2. Mark-Recapture Sampling

Tell me about Quadrats

for stationary organisms

1. frame of a given size that is placed at random within a habitat

2. Count is taken of population size within quadrat

3. Used to extrapolate size of entire population

quadrat sampled may fall in a clump

(overestimation)

quadrat sampled may fall between clumps

(underestimation)

Tell me about Mark-Recapture Sampling (Steps)

for mobile organisms

1. Group of organisms is captured, marked in some way and released

2. After allowing enough time for marked organisms to mix randomly into population, researchers capture a second sample of organisms

3. Proportion of marked to unmarked organisms in second sample is used to estimate overall population size

Tell me about Mark-Recapture Sampling (Rationale)

You can measure proportion of marked individuals in second sample:

(i.e. 10_{first sample RECAPTURED} out of 100_{second sample} = 10%)

Which is equal to proportion of all marked organisms in population

(i.e. if 50_{first sample TOTAL} were marked, then that’s 10% of all individuals, so population size is 500)

What is the Mark-Recapture Sampling Equation?

What does Mark-Recapture Sampling accuracy depend on?

• equal chance of all organisms being captured

• ratio of marked to unmarked individuals is constant (i.e. marking does not affect chance of survival)

• during study period population size is constant