C4.1 Populations & Communities

Population

Group of individual organisms of the same species living in a given area

Examples of types of interaction between individuals in a population

• Competition for food

• Cooperation to avoid predation

Random Sample

Every member as an equal chance of being selected

Sample error

Difference between the true and estimated value

Quadrat

Frame that is fixed size and used for random sampling

Capture-mark-release-recapture steps

1. Capture

2. Mark → represented as M

3. Release

4. Recapture → represented as N

5. Calculate Lincoln index

Formula for Lincoln Index

(M × N) ÷ R (recaptured with the marks)

Assumptions of capture-mark-release-recapture

• No migration

• No deaths/births

  • The mark is visible

Carrying Capacity

Maximum population size of an environment can support

Density-independent

Substance having the same effect no matter the population size

Density-dependent

Organism having an increasing effect when the population is bigger

When does exponential growth

When density-dependent factors are not effective or movement into a new niche where resources are abundant

Community

Several populations living and interacting with each other

Intraspecific relationship

Relationship between individuals of the same species

Competition

Organisms occupying the same ecological niche

Cooperation

Organisms mutually beneficial relationship

Intraspecific relationship

Relationships between different species

Herbivory

Primary consumers eating primary producers

Predation

One species kills and eats another species

Interspecific competition

Two different species competing for same resource

Mutualism

Two species both benefit for each other

Parasitism

A parasite living in/on the host

Pathogenicity

A pathogen living inside a host

How mutualisms works in root nodules

• Pea plants developing nodules that protect the bacteria from consumers

• Rhizobium bacteria → absorbs nitrogen, helping plant avoid an N deficiency

How mutualisms works in Mycorrhiza in orchids

• Orchids provide carbohydrates from photosynthesis for the fungus to use as an energy source

  • Fungus absorbs and supplies nutrients from the soil that the plant needs → water, nitrogen, phosphorus

How mutualisms works in Zooxanthellae in hard corals

• Coral provides protected environment close to the surface where algae can absorb light and also carbon dioxide from respiration

  • Zooxanthellae algae provide carbohydrates and oxygen from photosynthesis

Endemic species

Species occuring naturally in an area

Alien species

Species that are introduced outside their range by human activity

Invasive species

Alien species that spread rapidly because of the lack of density-dependent factors

H0

(known as the null hypothesis) Two species are distributed independently

H1

(known as the alternative hypothesis) Two species are associated

Top down

Something from higher in the food chain affects a lower level

Bottom up

Something from a lower level affects a higher one

Allelopathic agents

Secreted by plants into the soil to kill other plants

Mesocosms

Enclosed environments that allow a small part of a natural environment to be observed under controlled conditions