3.7.4 Populations in Ecosystems

ecosystem

made up of organisms living in a community (biotic) + the non-living components in environment (abiotic)

population

a group of interbreeding organisms of one species in a particular place at a particular time

community

all the populations of different species living and interacting in the same habitat

habitat + microhabitat

-place where a community of organisms normally live in an ecosystem

-within each there are smaller units each with their own microclimate

niche

how an organism fits/adapts into the environment, the role of a species within its habitat e.g. biotic + abiotic interactions

-competitive exclusion principle = no two species occupy the same niche

carrying capacity

the maximum size of a population that an ecosystem can sustainably support

-affected by abiotic + biotic factors

abiotic factors

-temperature + pH = enzymes

-light = photosynthesis

-water + humidity = transpiration

biotic factors -competition

2 types: -intraspecific = when individuals of the same species compete e.g. mates, availability of resources - more resources = larger population

-interspecific = when individuals of the different species compete e.g. food, space - initially occupy the same niche but over time one’s population size will grow while the other shrinks

biotic factors -predation

effect of predator-prey relationship cycle

-prey is eaten by predator so predator population increases + prey population decreases

-fewer prey means increased competition for food so predator population decreases

-fewer predators means more prey survive so prey population increases + repeats

types of quadrat

-frame quadrat = place in different locations within the area being studied, abundance of each species then recorded

-point quadrat = pins in each hole at set intervals, each species that touches pin is recorded

measuring abundance

-number of individuals in a species in a given area

can measure by:
-frequency = likelihood of particular species in a quadrat
-percentage cover = estimate of the area within a quadrat that a particular plant species covers

random sampling method

1) mark out grid of known area

2) random number generator for coordinates

3) place quadrat at coordinates

4) use large number of quadrats selected at random

5) measure number of species in each quadrat

6) repeats + large sample size = representative

7) use mean number = total number or % / number of quadrats or total size = mean number x number of quadrats

systematic sampling method

quadrats placed at set intervals along a belt transect

mark-release-recapture method

1) a set of organisms caught and then marked using a non-toxic tag on back + then released back
2) after a period of time to allow population to distribute randomly, the community is revisited + another sample is captured

3) the number of marked individuals is counted + USE EQUATION

mark-release-recapture equation

estimated population size =

total number of individuals in first sample x total number of individuals in second sample / number of marked individuals recaptured

mark-release-recapture assumptions

-proportion of marked to unmarked individuals in second sample is the same as proportion of marked to unmarked individuals in population as a whole

-few deaths and births

-method of marking is not toxic or makes individuals more prone to predation

-mark/label is not lost or rubbed off

primary succession + pioneer species

-where an area previously of no life is colonised by a species

-the first species to colonise the area

process of SUCCESSION

1) pioneer species numbers increase as they can survive hostile conditions

2) they change the environmental conditions less hostile/change abiotic factors such as provide food for other species

3) the change in conditions is more suitable for different species better adapted so out-compete pioneer species so their numbers decrease

4) greater species diversity/richness - more habitats and food sources

5) eventually reaches climax community

climax community

-same species present

-abiotic factors constant

-stable populations

secondary succession

occurs when land has already sustained life but is cleared so the soil remains

-more rapid than primary

conservation

the protection and management of species and habitats in order to maintain biodiversity

methods of conservation

-succession management

-seed banks

-captive breeding

-fishing quotas

-protected areas

plagioclimax

name for climax community when succession is stopped artificially to preserve an ecosystem