Biol. Unit 4, Chapter 1 - Populations

Summary of populations, chapter 1 of unit 4.

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  • Created on: 24-11-12 10:49
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Ajay Rai
Ecosystem ­ a group of interrelated organisms and their physical environment in a particular
Habitat ­ the part of an ecosystem where organisms live.
Population ­ all organisms of one species living in a particular habitat.
Community ­ all populations of all the species that live together in a particular ecosystem or
Abiotic factors ­ the non living, physical conditions in an ecosystem.
Biotic factors ­ the effects of the activities of living organisms on other organisms.
The way of life of a particular species in a habitat is called its ecological niche. Organisms of
different species, with different niches, can coexist in a community because they don't compete
for the exact same resources.
When two species occupy the exact same niche one is usually outcompeted, normally due to
the other being better at using the food supply and protecting itself from predators.
There are two types to use, random and systematic.
A quadrat is a defined area within which data is collected. They are usually used for collecting
plant data, or sessile (stationary for long periods of time) animals.
Percentage cover is useful when recording plant data as it is relatively impossible to tell when a
plant starts and ends:
Lay a frame quadrat over selected area.
Count the number of whole and half squares occupied by species.
Calculate this as a percentage of the whole quadrat area.
Repeat for all other species in quadrat.
Point quadrats are also useful as they are small and their areas are single points. They're an
excellent way of determining percentage cover of all different plant species in areas of relatively
short vegetation.
Line and belt transects are the two types of transects also available to use. For both, you start
by running a piece of string or tape along the sample line. For the line transect you record the
species of plant that touch the tape. This however can be impractical if vegetation is sparse, as
suitable intervals along the tape would have to be chosen. For the belt transect you place frame
quadrats so that one edge lies against the tape, recording the organisms within each quadrat.

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Ajay Rai
This can also be time consuming so regular intervals can be chosen, though this is called an
interrupted belt transect.
Catch a large sample of animals.
Mark animals in such a way that no harm comes to them, or predators aren't attracted.
Release marked animals back into habitat allow 1 ­ 2 days for them to mix with the rest of the population.…read more


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