populations in ecosystems Flashcards
Define ecology
study of inter-relationships between organisms and their environment
Define the term abiotic factor
Non living factors in an environment eg temperature or rainfall
Non living factors in an environment eg temperature or rainfall
living factors in an environment eg competition and predation
Define ecosystem
dynamic system made up of a community and all of the non living factors of its environment
Name two major process that occur within an ecosystem
-flow of energy
-cycling of elements
Define population
group of individuals of the same species occupying the same habitat at the same time and can interbreed
Define community
the populations of different species in a particular place at the same time
Define habitat
the place where an organism normally lives
Define microhabitat
a smaller unit within a habitat with its own microclimate
Define niche
how an organism fits into its environment (where the organism lives and what it does there)
Why do we describe populations as dynamic?
they vary in size and composition over time
Why is it necessary to use a logarithmic scale to plot growth curves for rapidly reproducing organisms?
So that all of the data can be represented on the same axis
Define limiting factor
factor that limits the growth of a population
State the factors that affect the size of a population
abiotic and biotic factors affect rate of growth and size of a population
Define carrying capacity
the size of population of a species that can be supported by the ecosystem
Describe how temperature affects a population size
-different species have different optimum temperatures.
-Temperatures above or below these may slow/denature enzymes in cold blooded animals or require excessive energy use to maintain in warm blooded animals
Describe how light affects population size
-Light is required for photosynthesis.
-More light, more photosynthesis, more biomass both for plant survival and for animals to feed on
Describe how pH affects population size
-pH affects action of enzymes.
-Organisms have an optimum pH and will not survive well in pH away from optimum
Describe how water affects population size
-In scarce water conditions only well adapted organisms survive.
Describe how humidity affects population size
-in low humidity transpiration and water loss increase.
-Plants and animals well adapted to tolerate low humidity will have larger population size
Why is it necessary to use a logarithmic scale to plot growth curves for rapidly reproducing organisms?
So that all of the data can be represented on the same axis
Describe competition
when 2 or more species share a resource that is insufficient to satisfy their requirements fully
Describe intraspecific competition
competition between members of the same species
Describe interspecific competition
competition between individuals of different species
Outline how the availability of resources affects a population
less resources - more competition - lower population size
Explain how competition causes smaller numbers of large trees in a forest rather than larger numbers of small trees
trees compete for resources - a few grow larger -this restricts resources for the others - which die
How does interspecific competition affect population size?
the population with the competitive advantage will increase in size while the other will decrease.
What is the competitive exclusion principle?
one species has the competitive advantage over another - population of less competitive species will decrease - until it becomes extinct
Describe the competitive exclusion principle in terms of niches
when resources are limiting no two species can occupy the same niche
Suggest how an increased food supply may result in a population increase
More food - more individuals survive - increased reproduction - increase in population
Define predator
organism that eats another organism
Define prey
organism that is eaten by another organism
Comment on the evolution of predators and their prey if extinction has not occurred
predators evolved to be more effective at catching prey - prey evolved simultaneously to be more effective at avoiding predators
Explain why it is difficult to obtain data on predator and prey populations in natural environments
it is not possible to count all individuals
Describe the predator prey relationship
-predator eats prey and reduces prey population -fewer prey means greater competition for food amongst predators
-predator population decreases due to lack of food
-less predators so less prey eaten and more survive and reproduce
-prey population increases
-repeat
Suggest why fluctuations in natural predator prey populations is not generally severe
a range of food is available to the predators
Why is sampling done in ecology?
-To find the abundance of organisms in an area when it is not possible to count every one individually, too time-consuming and is likely to cause damage.
Describe two types of quadrats and describe the suitable conditions for their use.
-A point quadrat > horizontal frame with long vertical pins > Any plant touching the pin is counted > Useful for small areas and plants which grow low to the ground.
-A frame quadrat > organisms within the frame are counted > They vary in size and an appropriate size should be chosen depending on area of the survey and size of the organisms.
Explain the use of random sampling
-Random sampling is used to get estimates of population size within a study area.
-It can also be used to investigate the effects of an abiotic factor if that factor is also recorded at each quadrat location.
-Random sampling avoids bias. It can be used to compare species composition in two or more different areas.
Explain the use of systematic sampling
-This is used to assess abundance and distribution, -particularly where there are gradual changes in an abiotic factor and subsequently the communities present.
-A transect can be used to document changes in communities over a distance.
Define abundance
Abundance is the number of individuals of a species within a given area.
Describe two measures of abundance
- Frequency- the likelihood of a particular species occurring in a quadrat. E.g. if a species occurs in 10 out of 20 quadrats its frequency would be 50%.
-Percentage cover is an estimate of the area within a quadrat that a particular plant species covers. Individual plants do not need to be counted.
Explain the use of Mark-release-recapture
-This is a method of measuring abundance of motile species which could not be counted using a quadrat
-they run away, they are hidden, and are therefore difficult to catch.
-A known number of animals are caught, marked in a non-harmful way and then released .
-At a later time a given number of individuals are caught in the same area and the number of marked individuals is recorded.
-A calculation is carried out- total number in first sample x total number in second sample/number of marked individuals recaptured- gives an estimate of population size
Explain why Mark-release recapture is not always reliable
-A number of assumptions are made:
-the proportion of marked to unmarked in the second sample is representative of the population as a whole.
-The marked individuals in the first sample spread out into the population.
-The population remains stable between surveys, i.e. there is no immigration or emigration, or no deaths or births.
-The marking does not hamper the survival of the individuals.
-The marking will not be removed between surveys.
Suggest what is meant by the statement ‘ecosystems are dynamic’
they change on a daily basis as populations fluctuate
Define succession
the changes over time in the species that occupy a particular area
Describe what happens at each stage of succession
new species colonise an area - the new species changes the environment
Describe two effects of a new species (B) altering an environment during succession
- environment becomes less suitable for existing species (A) which is outcompeted
- environment becomes more suitable for another species (C) which then outcompetes species B”
How can successional changes affect biodiversity?
-new species alter abiotic environment
-making it less hostile for other species, which survive
-new communities are formed
-biodiversity changes
Describe a pioneer species
organisms that colonise inhospitable environments
Describe the features of a pioneer species
-asexual reproduction (fast)
-large quantities of wind dispersed seeds/spores (reach isolated environments)
-rapid germination of seeds (fast)
-photosynthetic (light tends to always be available)
-nitrogen fixing (poor soil)
-tolerant to extreme condition”
Describe how a pioneer species might change abiotic factors in the environment
weathering of rock produces ‘soil’ decomposition of pioneer species adds nutrients to the soil
Define climax community
Balanced equilibrium of species, few/no new species replacing established, high biodiversity
What determines succession in animals?
the plant species available for them to feed on and live in
State 5 common features of succession
-abiotic environment becomes less hostile
-greater variety of habitats and niches
-increased biodiversity
-more complex food webs
-increased biomass
Describe secondary succession
succession that occurs on land that has previously sustained life but has been altered (eg by fire)
Describe primary succession
succession from bare rock or barren land
