populations in ecosystems

all populations of different species in the same area at the same time

a community and the non-living components of an environment e.g. tropical rainforests, deserts e.t.c Ecosystems are dynamic and can be of different sizes when we say that an ecosystem is dynamic we mean that its characteristics can vary over time

A niche is an organism’s role within the ecosystem. Each species occupies its own niche this is influenced by abiotic and biotic factors

impact of interactions between organisms e.g. competition, predation e.tc.

non-living factors in an ecosystem

the maximum population size an ecosystem can support

• Ph • soil quality • temperature • oxygen levels • CO2 levels • light intensity plants and animals are adapted to abiotic factors, which develop through the process of natural selection

species diversity and population size is larger when abiotic conditions are less extreme because there is a higher chance that species survive and reproduce and therefore pass their allele to the next generation

interspecific competition intraspecific competition predation

it is when members of DIFFERENT SPECIES compete for the SAME RESOURCES that are in LIMITED SUPPLY e.g. light, water, food e.t.c The BETTER ADAPTED INDIVIDUAL is more likely to survive and reproduce

it is when members of the SAME species compete for RESOURCES and a mate these resources can be light, water food e.t.c

when they are competing for mates, the more well-adapted individuals will be able to perform more “impressive” courtship display pr may have features in better conditions e.g. neater feathers so they will be more likely to attract a mate and reproduce to produce fertile offspring possessing the advantageous alleles that make them more advantageous in getting a mate this is another factor that affects population size

predation is another factor that affects population size It is the interaction between predator and prey

predation has a cyclic fluctuation the predator population increases as the prey increases because there are more food resources, increasing survival the prey population increases as predator population decreases as they’re less likely to be predated on so survive

• quadrants • belt transects • mark- release recapture technique

• place 2 tape measures at right angles to create a gridded area to take samples from • use a random number generator to generate coordinates to take samples (avoid bias) • Place quadrat on the coordinate and either count the abundance of the species or calculate species cover • Repeat at least 30 times ( to get a representative sample of the whole population)

• tape measures are placed through a NON-UNIFORM ECOSYSTEM e.g. a rocky beach (belt transects are a crucial environment as it would be difficult to place a quadrant here) • quadrats placed at intersects along the transect to measure the impact of changes in the environment (in an environment that is non-uniform, the abiotic factors are likely to be different) on different populations of species

this is used for motile organisms e.g. insects If we used a quadrant for motile organisms, they may move out of the quadrant when sampling leading to inaccuracies

• animals are trapped and marked with a substance that must be non-toxic ( so it does not kill them), weather resistant (so it does not wash off) and not impacted by predation or reproduction (as this would lead to fluctuation in population size which is not what we want in our experiment) • released and left to distribute themselves in the populations • They’re recaptured a few days later and a 2nd sample is taken. This is repeated 10 times * this is done to get a represented and reliable result

population size = size of 1st sample x size of 2nd sample/ number of marked recaptured

• enough time must pass in order for organisms to distribute themselves • no migration (they don’t leave the boundary of the investigation) • no births or deaths (so it does not affect the population size)

succession changes in an ecological community overtime

• A pioneer species colonises bare rock or sand • Pioneer species are adapted to survive harsh abiotic conditions and change abiotic factors to become less harsh through their death and decomposition • moss and smaller plants can now survive, and they further increase the depth and nutrient density of the soil as they die • this process continues and continues and larger plants can survive because the abiotic conditions are less harsh and change the environment • each new species may change the environment in a way that the previous species can no longer survive as they become outcompeted e.g. larger plants block the sunlight for smaller plants • these changes result in a less hostile environment and increase biodiversity • Final stage of succession is a climax community

it is a community made of mainly one species (usually trees)