7.4 Populations in ecosystems Flashcards
(13 cards)
Population
A group of organisms of the same species in a particular habitat at a particular time. The individuals in the population are able to breed with each other (ie there is no reproductive isolation within a population - the group of organisms is one gene pool).
Community
Populations of different species living in the same habitat form a community.
Habitat
The place in an ecosystem in which a community lives.
Ecosystem
Ecosystems are dynamic systems, in which biotic and abiotic (physicochemical) factors interact. An ecosystem is the dynamic interaction between the community and the abiotic components of its environment. Ecosystems can range in size from the very small to the very large.
Niche
Niche: the role of a species in a habitat (its interaction with the habitat and with other species in the community).
A species is adapted to its niche.
Niches are occupied by species.
Within a habitat, a species occupies a niche governed by its adaptation to both abiotic and biotic conditions.
Take any two species in a community - the more dissimilar their niches, the less competition there will be between them.
Carrying capacity
An ecosystem supports a certain size of population of a species,
called the carrying capacity. This population size can vary as a
result of:
* the effect of abiotic factors
* interactions between organisms: interspecific and intraspecific competition, and predation.
Primary succession
Primary succession is the gradual change in community from pioneer species to climax community.
At each stage in succession, certain species may be recognised
which change the environment so that it becomes more suitable for
other species with different adaptations. The new species may
change the environment in such a way that it becomes less
suitable for the previous species.
Changes that organisms produce in their abiotic environment can
result in a less hostile environment and change biodiversity.
Colonisation by pioneer species…
Pioneer species change the conditions in the habitat, for example by providing food for primary consumers, or organic matter for decomposers…
The environment has become a little bit less hostile, making it more suitable for other species…
The new species change the habitat further, and so in turn are out-competed by other species better adapted to the new conditions…
As each stage of the community changing passes, biodiversity increase, and the environment becomes more stable (and so less hostile)…
Eventually the climax community is established.
Secondary succession
Happens on ground that previously supported a community which has been lost, maybe due to flood, deforestation or wildfire. A soil is already present.
Pioneer species
Pioneer species are:
Never consumers (nothing to consume).
Often asexual (no mates), can quickly colonise an area without needing to find mates.
Wind dispersed(no animals to carry seeds).
Able to tolerate hostile environments eg extreme fluctuations in temperature.
The pioneer stage has:
Low species richness
Unspecialised niches
Low biodiversity
Less complex trophic structure (maybe no consumers at all to start with)
Climax community
When the same stable community of species remains present over a long time, without being out-competed. Abiotic factors will remain more or less constant, and populations will remain stable, fluctuating around carrying capacity.
Conservation
Conservation involves management of ecosystems to try and reduce biodiversity loss.
Conservation of habitats frequently involves management of succession, to prevent a rare community being out-competed.
Reasons to do conservation:
To protect endangered species
To maintain or increase biodiversity
To protect habitats (which provides niches)
To conserve land (and ways of life) for indigenous communities
To provide ecotourism opportunities
To reduce the impact of climate change
To reduce erosion
To protect future sources of medicines
Mark-release-recapture
(number in sample 1) x (number in sample 2) / number marked in sample 2
Capture a sample, mark and release. Allow time to reintegrate, then take a second sample in the same way and count marked organisms.
Marking should not harm the organism, affect their chances of survival, or be easily removed.
Mark-release-recapture assumes there is no immigration or emigration, and that there are no births or deaths.
The size of a population can be estimated using:
Randomly placed quadrats, or quadrats along a belt transect, for slow-moving or non-motile organisms.
The mark-release-recapture method for motile organisms.
