Abiotic factors = the physcial or non-living aspects to an ecosystem. These include:
• Climatic factors, such as temperature; water/humidity; light/shade;current (wind/water), frost
• Edaphic (soil) factors, such as pH; mineral supply; soil texture; soil moisture.
• Topographic factors, such as altitude, slope, aspect .
• Human factors, such as pollution.
• Catastrophes, such as floods and fire .
Abiotic factors can vary within a habitat, giving microclimates in microhabitats.
Abiotic factors tend to be density-independent factors, i.e. the size of the effect is independent of thesize of the population. For example a low light intensity will limit plant growth regardless of the number of plants present.
Many abiotic factors vary with the seasons, and this can cause a periodic oscillation in the population size.
Biotic factors are all the living aspects of an ecosystem. I.e. food, competitors, predators, parasites and pathogens.
Biotic factors tend to be density-dependent factors, i.e. the size of the effect depends on the
size of the population. For example competition will be greater the greater the population.
- Competition for resources (such as food, space,water, light, etc.) between
members of different species.
- In general one species will out-compete another one.
- Tends to have a dramatic effect on populations.
Biotic Factors 2
- Competition for resources between members of the same species.
- Is more significant than interspecific competition, since member of the same species have the same niche and so compete for exactly the same resources.
- Tends to have a stabilising influence on population size because it is density-dependent.
- If the population gets too big, intraspecific population increases, so the population falls again.
- If the population gets too small, intraspecific population decreases, so the population increases again.
- is also the driving force behind natural selection, since the individuals with the “best” genes are more likely to win the competitio nand pass on their genes.
Biotic Factors 3
- The populations of predators and their prey depend on each other, so they tend to show cyclical changes.
- If the population of the prey increases, the predator will have more food, so its population will start to increase.
- This means that more prey will be eaten, so its population will decrease, so causing a cycle in both populations.
Parasitism and Disease
- Parasites feed on larger host organisms, harming them.
- Parasites and their hosts have a close symbiotic relationship, so their populations also oscillate.
- If the population of parasite increases, they kill their hosts, so their population decreases.
- This means there are fewer hosts for the parasite, so their population decreases.
- This allows the host population to recover, so the parasite population also recovers.
Biotic Factors 4
- In harsh environments (very cold, very hot, very dry, very acid, etc.) only a few species will have successfully adapted to the conditions so they will not have much competition from other species.
- But in mild environments lots of different species could live there, so there will be competition.
- In other words in harsh environments abiotic factors govern who survives.
- in mild environments biotic factors (such as competition) govern who survives.