2 Populations In Ecosystems Flashcards
Define community
Populations of different species in a habitat
Define ecosystem
A community, plus all the abiotic conditions in the area in which it lives. Ecosystems can be small or large.
Define niche.
Describe how an organism fits into the environment. A niche refers to where an organism lives and what it does there. Includes all the biotic and abiotic conditions to which an organism is adapted to in order to survive, reproduce and maintain a viable population. No 2 species occupy the same niche.
Why does every species occupy a different niche?
- the niche a species occupies within its habitat includes:
- it’s biotic interactions eg. The organism it eats, those it’s eaten by
- it’s abiotic interactions eg. The oxygen organism breathes in and CO2 breathes out.
Explain how the size of a population can be estimated using the mark-release-recapture method.
- capture sample of species using an appropriate technique
- mark them in a harmless way eg. By putting spot of pain on them
- release them back to habitat
- wait a week, then take a second sample from same population
- count how many of second sample are marked
- use equation to estimate total population size.
What is the equation for the mark-release-recapture method?
Total population size= (number caught in 1st sample x number caught in 2nd sample) / number marked in 2nd sample.
What are the assumptions when using the mark-release-recapture method?
- marked sample had enough time + opportunity to mix back in with the population
- marking hasn’t affected the individuals’ chances of survival (eg by making them more visible to predators) and the marking itself is still visible
- there are no changes in population size due to births, deaths and migration during the period of study.
How does temperature ( abiotic factor) affect population size?
- each species has different optimum temp at which it’s best able to survive.
- further away from this, fewer individuals in pop able to survive, and smaller is pop that can be supported.
- in plants + cold-blooded animals, as temp fall below optimum, enzymes work more slowly + so metabolic rate is reduced. Pops therefore have smaller carrying capacity. At temp above optimum, enzymes work less efficiently because they gradually undergo denaturation.
- in warm-blooded animals, further temp of external environment is from optimum, more energy organisms expend trying to maintain normal body temp. Leaves less energy for individual growth + so they mature more slowly + their reproductive rate slows. Carrying capacity of pop reduced.
How does light (abiotic factor) affect population size?
- light is basic necessity in life
- rate of photosynthesis increases as light intensity increases
- greater the rate of photosynthesis, faster plants grow + more spores or seeds they produce
- carrying capacity therefore potentially greater. In turn, carrying capacity of animals that feed on plants is potentially larger.
How does pH (abiotic factor) affect population size?
- affects action of enzymes
- enzyme has optimum pH at which it operates most effectively
- population of organisms larger where appropriate pH exists + smaller, or non-existent, where pH different from optimum.
How does water and humidity (abiotic facto) affect population size?
- where water scarce, populations small + consist only of species that are well adapted to living in dry conditions
- humidity affects transpiration rates in plants + evaporation of water from bodies of animals
- in dry air conditions, populations of species adapted to tolerate low humidity will be larger than those with no such adaptations
Describe intraspecific competition.
Occurs when individuals of same species compete with one another for resources. It’s availability of such resources that determines size of population. Greater availability, larger pop. Lower availability, smaller pop.
Give an example of intraspecific competition.
Limpets competing for algae, which is their main food. More algae available, larger limpet population becomes.
Describe interspecific competition.
Occurs when individuals of different species compete for resources. When pops of 2 species in competition 1 will normally have competitive advantage. Pop of this species gradually increase in size while population of other will diminish. If conditions remain same, this will lead to complete removal of 1 species. This is known as competitive exclusion principle.
Explain how interspecific competition influences population size.
Link to birth + death rate of individuals in pop. Increase in food supply doesn’t necessarily mean there’ll be more individuals. Could just result in bigger individuals. Decrease in food supply could lead to individuals dying of starvation + directly reduce size of pop. Increase in food supply means more individuals likely to survive + so there’s increased probability that they,, produce offspring and pop will increase.
Explain what is meant by predation.
Occurs when one organism is consumed by another. When pop of a predator and a pop of its prey brought together in a lab, prey usually exterminated by predator. Because range + variety of habitat provided normally limited to confines of lab. In nature, area over which pop can travel is greater and variety of environment more diverse. Prey can escape because fewer there are the harder they are to find and catch. Therefore, although prey pop falls to low level, it rarely becomes extinct.
Describe the effects of predator-prey relationships on population size.
- predators eat their prey, reducing pop of prey
- fewer prey available, predators in greater competition with each other for prey left
- predator pop reduced as some individuals unable to obtain enough prey for their survival or to reproduce
- fewer predators eating prey, so more prey survive and reproduce
- prey pop therefore increases
- More prey available as food, predator pop in turn increases
Why should the size of the quadrat be considered when using quadrats?
Size will depend on size of plants or animals being counted + how they’re distributed within the area. Larger species require larger quadrats. Where pop of species not evenly distributed throughout area, large number of small quadrats will give more representative results.
Why should the number of sample quadrats to record within the study area be considered when using quadrats?
Larger number of sample quadrats, more reliable results will be. As recording of species within quadrat is time-consuming, a balance needs to be struck between reliability of results and time available. Greater number of different species present in area, greater the number of quadrats required to produce reliable results for a valid conclusion.
Why should the position of each quadrat within the study area be considered when using quadrats?
To produce statistically significant results random sampling must be used.
Describe how a transects is used to obtain quantitative data about changes in communities along a line.
Lines called transects used to help find out how plants are distributed across an area. In belt transects, quadrats placed next to each other along the transect to work out species frequency and % cover along transect. To cover larger distances, quadrats can be placed at intervals along the line. This known as interrupted belt transect.
Define abundance.
The number of individuals of a species within a given area.
How does frequency measure the abundance for species that don’t move around?
Frequency is the likelihood of a particular species occurring in a quadrat. This method useful where species is hard to count. Gives a quick idea of the species present and their general distribution within an area. However, doesn’t provide information on density + detailed distribution of a species.
How does percentage cover measure the abundance for species that don’t move around?
Percentage cover is an estimate of area within a quadrat that a particular plant species covers. Useful where species is particularly abundant or is difficult to count. Data can be collected rapidly + individual plants don’t need to be counted. However, less useful where organisms occur in several overlapping layers.
