3.7 genetics, populations, evolution and ecosystems Flashcards
population size can vary as a result of
- the effect of abiotic factors
- interactions between organisms ; intraspecific and interspecific competition and predation
2 types of competition
- intraspecific
- interspecific
competitive exclusion principle
- when 2 species are competing for limited resources, one will typically have a competitive advantage and outcompete the other
- this may be avoided if one or both species have adapted to utilise other resources or a different area of the habitat
size of a population can be estimated by 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. The
assumptions made when using the mark-release-recapture
method.
define exponential growth of a population and state why this is not possible in real life
exponential growth of a population is the continuous growth in population size.
- exponential growth is only possible where there is an infinite supply of resources.
- in real ecosystems, this is not the case, hence exponential growth is not possible
how might temperature affect population size
- extreme temperatures can affect enzyme action
- can directly affect the survival & distribution of a species. Species adapted to thrive in specific temperature ranges will form larger populations in these areas
- ff the temperature of a habitat is significantly lower/higher than the organism’s optimum temperature, the organisms in that habitat cannot grow as efficiently.
- more energy will be spent maintaining body temperature which means less energy will be available for growth and reproduction, limiting the population size (and the opposite for idea temperature conditions)
how might light affect population size
- low light levels = less photosynthesis = smaller, slower growing, fewer plants = reduced food for primary consumers = knock on effect for all trophic levels
- opposite in high light levels: more food for primary consumers, carrying capacity increases
how might pH affect population size
- extreme pHs affects enzyme action
- All enzymes have an optimum pH. The population is larger when the optimum exists and smaller when the pH is different.
- The pH of water can also affect the aquatic organisms that are found there. Different species have evolved to survive at different pH levels found within water
how might water and humidity affect population size
- where water is scarce, populations are small and consist of a few well-adapted species.
- Humidity can affect transpiration and evaporation rates.
- Many plants cannot survive in waterlogged soils. Their roots are unable to respire, they rot and the plant dies.
- Other plants, such as pitcher plants, grow best in bogs where the moisture levels are high.
how might intraspecific competition affect population size
- when resources are abundant, the population size increases. This increases intraspecific competition since resources will need to be shared between more organisms, which causes population size to decrease.
- this pattern causes population numbers to fluctuate around the carrying capacity (the maximum number of organisms that an ecosystem can support).
- species that have adaptations that allow them to gain resources better than other species are more likely to survive and reproduce
how might interspecific competition affect population size
- interspecific competition means that resources have to be shared between the different species so there will be less available to both.
- this means both species will have less energy for growth and reproduction, so population numbers of both species will decrease.
- for example, leopards and lions show interspecific competition since they both feed on the same prey.
define succession
the gradual change in a community/ecosystem (all the organisms of different species) over time. There are 2 types: primary and secondary
why does succession occur?
succession occurs because the conditions (abiotic and biotic) in a habitat are gradually changed by the existing species living in it.
- the new conditions are less hostile and so more suitable for a different combination of species and less suitable for the previous species, causing the previous species to be outcompeted.
define primary succession
- primary succession is when an ecological community develops in the absence of organisms and soil (i.e. from bare rock).
- this may happen after a volcanic eruption which results in the formation of new rock or if the sea level lowers and exposes new land, glaciers retreating and depositing rock
define secondary succession
- when an ecological community develops from a barren landscape in which soil is present, with some organisms living in it, including spores and seeds, but the existing community has been destroyed so the soil is bare.
- e.g. after a forest fire, on an abandoned agricultural land. due to the presence of some soil and organisms, secondary succession occurs much faster than primary
