2.1 Species and Populations

What is a species?

A group of organisms sharing common characteristics that interbreed and produce fertile offspring

What is a habitat?

An environment which a species lives. This consists of abiotic (non-living) and biotic (living) factors

What is a niche?

Where, when and how an organism makes a living

***NOTE:*** *there are differences between what niche the species occupies (fundamental niche) and what it actually occupies (realised niche).*

What is a fundamental niche?

The full potential of what can be occupied

What is a realised niche?

What the species actually occupies

What is a population?

Group of organisms of the same species living in the same area at the same time and are capable of interbreeding

What are abiotic factors?

Non-living factors that influence the organisms and ecosystems

What are biotic factors

Living components of an ecosystem that directly or indirectly affect another organism

What are ecosystems?

Made up of organisms and the physical environment and the interactions between the living and non-living components between them.

Examples of abiotic factors

sunlight, temperature, salinity, pH, pollutants

Why are abiotic factors important?

They determine ecosystems and their adaptations

examples of biotic factors

organisms, their interactions or their work

INCLUDES: predation, herbivory, parasitism, mutualism, disease and competition

What is the carrying capacity?

The maximum number of a species that can be sustainably supported by a given area

What are limiting factors?

Factors that slow down growth of a population as it reaches its carrying capacity

What are population dynamics?

The study of factors that cause changes to population sizes.

All interactions result in one species having an effect on the population dynamics and the carrying capacity of the environment.

What is symbiosis?

A relationship where two organisms live together

*symbiosis*

what is parasitism?

A relationship between two species where one (the parasite) lives in or on the other (the host) gaining its food from it.

e.g. ticks, tape worms

Two types of parasites are…

1. Endoparasites: live inside the host

2. Ectoparasites: live on the surface of the host

*symbiosis*

What is mutualism?

Relation between two or more species where all benefit and none suffer

Example of mutualism

i.e. lichen

= fungus on top of lichen benefits by obtaining sugars from algae

= algae benefits from minerals and water fungus absorbs and passes onto algae

*symbiosis*

What is commensalism?

When one partner is helped and the other is not significantly harmed

Example of commensalism

i.e. fern growing halfway up a tree trunk

What is competition?

when resources are limited, populations compete in order to survive

Two types of competition

**intraspecific competition:** Within species

**interspecific competition:** between different species

* no two species can occupy the same niche so the degree to which niches overlap determines the degree of interspecific competition

What is competitive exclusion?

One species out-competes the other

What is predation?

When one animal, the predator, eats another animal, the prey

• includes plants eating plants

• can be beneficial since it strengthens the breeding pool by eliminating weaker organisms

What is herbivory?

Animals that feed on plants

*(some plants have defence mechanisms against this)*

What are S and J population curves?

Describe a generalised response of populations to a particular set of conditions

What are S curves?

• start with exponential growth (no limiting factors affect the growth at first)

• above a certain population size, the growth rate slows down resulting in a population of a constant size

• Numbers stabilise at the carrying capacity

What are J curves?

• Shows a boom and bust pattern

• rapid growth continues well past carrying capacity

• Then suddenly collapses (dieback)

• Does not show gradual slow down of population size

• Controlled by abiotic factors