Populations in Ecosystems Flashcards
Habitat
the place where an organism lives
Population
all the organisms of a species in a habitat at a particular time which have the potential to interbreed
Community
populations of different species in a habitat
Ecosystem
a community, an all the abiotic conditions in the area in which it lives
Abiotic conditions
examples
the non-living features of an ecosystem, e.g. temperature, water availability
Biotic conditions
examples
the living features of an ecosystem, e.g. the presence of predators or food.
Niche
the role of a species within its habitat, e.g. what it eats, when and where it feeds
Adaptation
a feature that members of a species have that increases their chances of survival and reproduction
Can 2 species occupy the same niche?
not indefinitely, the species will compete with each other and 1 will be more successful, so will out-compete the other.
Biotic interactions of an organism
Interactions with other living organisms - what organisms it eats, what organisms it’s eaten by.
Abiotic interactions of an organism
Interactions with physical features - the oxygen an organism breathes in and the carbon dioxide it breathes out.
What types of adaptations can an organism have?
behavioural, physiological, anatomical.
Why are adaptations important?
they increase an organism’s chances of survival and reproduction, so organisms are more likely to survive and reproduce and pass the favourable alleles for adaptations on to offspring. Adaptations become more common in the population - this is natural selection.
Carrying capacity
The maximum stable population size of a species that an ecosystem can support.
Why can carrying capacity vary?
2 key factors
due to abiotic and biotic factors
Why can carrying capacity vary due to biotic factors?
3
Interspecific competition
Intraspecific competition
Predation
Why can abiotic conditions affect carrying capacity?
E.g. - explain non-opt temperature
When abiotic conditions aren’t ideal, organisms can’t grow as fast or reproduce as successfully.
When the temperature is significantly lower or higher than an organism’s optimum, they have to expend energy maintaining the right body temperature. Less energy is available for growth and reproduction, so population size decreases.
What is interspecific competition?
competition between members of different species
For what resources can interspecific competition occur?
Food water, habitats
What is intraspecific competition?
Competition between members of the same species
For what resources can intraspecific competition occur?
Food, water, habitats, mates
When does competition occur?
when 2+ organisms share a resource which isn’t large enough to satisfy all their needs.
Why can interspecific competition reduce carrying capacity?
The resources for both populations are reduced, so both population sizes are limited. E.g. food - both populations have less energy for growth and reproduction ==> lower population sizes.
Why can intraspecific competition reduce carrying capacity?
The cycle of how/ why population size constantly fluctuates.
Population size increases when resources are plentiful, and as pop. size increases, there are more organisms competing for these resources. Eventually, resources become limiting - there isn’t enough for all organisms, so population size declines.
Smaller population ==> less competition. Cycle starts again.
What is the competitive exclusion principle?
when 2 species are competing for a limited resource, the species that uses the resource most effectively will usually eliminate the other species - i.e. no 2 species can occupy exactly the same niche forever.
What needs to be linked in to show how a factor influences population size? Why?
Birth and death rates
E.g. more food may not mean more individuals in the short term, just bigger individuals.
How does food supply influence population size?
Decrease in food supply - individuals may die of starvation ⇒ reduces population size. Individuals also have less energy for growth and reproduction, so produce less offspring.
Increase in food supply - more individuals are able to survive, so there is a greater probability that individuals will produce offspring and population size will increase.
What is predation?
where an organism - the predator - kills and eats another organism - the prey.
Describe the typical predator-prey relationship.
6 stages
- Predators eat their prey. This reduces the prey population size.
- As fewer prey are available, the predators are in greater competition for the remaining prey.
- The predator population decreases in size as some individuals aren’t able to obtain enough prey to survive or to reproduce.
- With fewer predators remaining, fewer prey are eaten and more survive and can reproduce.
- The prey population increases in size.
- As more prey are available as food, the predator population increases.
Why are fluctuations in natural ecosystems not so severe?
organisms eat a wide range of foods and are able to escape the predator/shelter more easily.
Why are disease and climatic factors important in influencing population size?
They cause fluctuations which are important in evolution, as selection pressures mean that better adapted individuals are more likely to survive to reproduce.
Why should a sample be taken rather than investigating the whole population?
It is too time-consuming and expensive to investigate the whole population.
Why should sampling methods be random?
to avoid bias
How can a random sample of an area be taken?
By dividing the area into a grid using tape measures, then using a random number generator on a calculator to obtain a series of coordinates. Collect data at these coordinates.
What types of organisms can quadrats and transects be used to investigate?
slow moving or non-motile
What can quadrats be used to estimate?
percentage cover or number of organisms for each species
Why is it important to have a large sample size?
As this decreases the effect of chance on the sample, meaning the results are more likely to be representative.
Assumptions made in mark-release-recapture
7
- Marked: unmarked in 2nd sample is same as in whole population
- Marked individuals distribute themselves evenly
- No immigration/ emigration
- Few births or deaths
- Mark is not toxic
- Mark does not increase chance of predation
- Mark is not lost
What is the process of mark-release-recapture?
A known number of animals are caught, marked, and released back into the community. Later on, another sample of individuals is randomly collected, and the number of marked individuals is counted.
What is mark-release-recapture used for?
To estimate the population size for a species of motile organism
What is the equation for mark-release-recapture?
Estimated population size = total no. individuals in sample 1 X total no. individuals in sample2
/Number of marked individuals recaptured
Factors to consider when using quadrats and why
- Quadrat size - depends on the size and distribution of the organisms.
- Number of quadrats - larger number means more reliable results. This is limited by time.
- Position of each quadrat - must be random.
What is succession?
the process by which an ecosystem changes over time. Biotic conditions change as the abiotic conditions change.
What is primary succession?
happens on newly formed/exposed land, for example where a volcano has erupted to produce a new rock surface, or where a drop in sea level has exposed new land. There is no soil/ organic material to begin with, just bare rock.
Methods of estimating population size
• randomly placed quadrats, or quadrats along a belt transect, for
slow-moving or non-motile organisms
• the mark-release-recapture method for motile organisms.
Stages of primary succession
- colonisation by pioneer species - e.g. lichen, leads to soil formation.
- changes environment/
- makes the environment more suitable for different species with different adaptations, enabling other species to colonise
- biodiversity changes/ increases, the ecosystem becomes more complex and less hostile
- eventually a climax community is reached.
Pioneer species
the first species to colonise a new land surface.
Climax community
Steady state - the largest, most complex community an ecosystem can support.
What can changes organisms produce in their abiotic environment lead to?
a less hostile environment and changes in biodiversity
What does conservation of habitats frequently involve?
management of succession
What does conservation by managing succession mean?
Example
stopping an ecosystem from reaching its climax community, e.g. stopping heathland (where endangered species live) from becoming woodland
Methods of managing succession
allowing animals to graze, using managed fires
What are sessile organisms?
non-moving
What are the advantages of using a logarithmic scale to represent population growth?
Used when population growth is exponential - useful as a wide range of data can be shown and smaller values can be plotted more accurately.
Which abiotic features can reduce carying capacity?
temperature, availability of light or water, pH
