Abundance and distribution of organisms in a habitat

biogeography

study of species abundance and distribution

abundance

number of individuals in a species in a given area or volume

What is described first in a new habitat and why? (2)

physical features, determine the number and types of plants that live there

Why are plants described after physical features before animals? (2)

animals depend on the plants, so plants are described first

What are 3 examples of physical features that could be described in a new habitat?

soil type, rainfall through-out the year, temperature of habitat

How can you measure abundance of plant species? (3)

quadrat to calculate mean number of individuals in several quadrats of known area to find density number of plants per m², estimating percentage cover of a plant in which individuals are hard to recognise, estimating percentage frequency

How else can you measure abundance of animals? (2)

capture-mark-recapture process, Lincoln index

distribution

area or volume in which the organisms of a species are found

How can distribution be measured if a habitat is uniform? (3)

positions of outermost plants can be marked on a map and the area they surround can be measured, a small area may indicate that a species is under threat of extinction, helping to protect specific sites from mining or road building to reduce species loss

How can distribution be measured if a habitat is not uniform?

a transect can be used for displaying variation in organisms and its correlation with a changing abiotic factor

What is a transect? (2)

a line along which abundance is assessed at measured intervals, shows the organisms that lie on a line

What is a belt transect? (4)

shows abundance data for a given area at measured distances along the transect, a quadrat is placed at each co-ordinate along the transect and readings may be taken for density of chosen species, percentage frequency of chosen species, percentage area cover for all species

Why is a belt transect only suitable for assessing plants or sessile animals and not motile animals? (2)

motile animals move, so they may move from the area of the quadrat

How can you assess distribution of motile animals instead? (4)

use direct observation of individuals, their nests, faecal deposits, markings on vegetation