Populations and communities Flashcards
Define population
A group of organisms of the same species living in a particular area.
What four factors affect a population?
Birth, death, immigration, emigration
Describe the features of bacterial growth in a nutrient medium in closed conditions
Sigmoidal shaped curve:
- Lag phase - Nutrient assimilation, activating genes and producing necessary enzymes
- Exponential phase - Bacteria divide exponentially, no restriction to growth
- Stationary phase - A factor becomes limiting e.g. food, waste, space
- Decline phase - Death rate exceeds birth rate
What is the biotic potential?
The maximum rate of growth as seen by the exponential phase - The reproductive rate of a population under optimum conditions and unlimited resources
What is environmental resistance?
The restriction by the environment on the population reaching its max growth rate and its biotic potential. e.g. nutrient shortage or accumulation of waste.
What is the carrying capacity?
The max number of a population an ecosystem can support, determined by the resources available.
Draw a J shaped curve.
in book
What are J shaped curves representative of?
Characteristic of many protoctistan species
What are the two types of competition?
Interspecific and intra-specific
What is the competitive exclusion principle?
No two species can occupy the same ecological niche, therefore one species loses out.
What type of curve do you get with a predator prey graph?
Oscillating with the predator peaks and troughs lagging behind the preys, with the number usually lower than the number of prey.
What is the equation for population growth?
(Births + Immigration) - (Deaths + emigration)
What are the two types of species we deal with?
r-selected species and k-selected species
What are r selected species?
Opportunistic and grow very quickly, usually boom bust patterns of growth e.g bacteria and protoctistans
What are k selected species?
Have more stable populations and population size usually remains at carrying capacity. Emphasis on survival. e.g. humans
Features of r and k selected species?
in book.
What are the three types of population interactions?
- Mutualism - +/+ - both species gain, interaction necessary for both
- Predation - +/- - The predator gains and the prey loses
- Competition - -/- - Both species lose while interacting, species most affected is eliminated from its niche.
What is parasitism and how does it differ from predation?
Parasite - an organism that lives in or on another organism benefitting from it an causing it harm over a period of time. +/-, the difference is predators kill their prey to obtain nourishment, parasites do not.
Describe mutualism and give an example
Both species gain +/+, e.g. nitrogen fixing bacteria receive nutrients and protection inside the root nodules of leguminous plants. Lichens harbour green algae among their hyphae, the fungi absorbs water and nutrients used by the plant.
What is a pest and what is biological control?
Pest - A species that damages a commercial crop and causes economic damage
Biological control - Deliberately introducing an organism that will target and cause harm to the pest e.g. a predator, competitor
What are some benefits of biological control?
- Reduce the need for chemical pesticides/herbicides
- No bioaccumulation of waste in foods
- Development of resistance is unlikely
- If successful needs little additional action
What are the downfalls of biological control?
- Pest resurgence can occur
- Pest is unlikely to be totally eliminated
- Only works if the species can adapt and thrive
- Important the introduced species does not outcompete the native species
What is a community?
The total of all the populations in a particular area - The biotic component of an ecosystem
What is an ecosystem?
The abiotic and biotic component
What is succession?
The changes in an ecosystem over time, both biotic and abiotic.
Where does primary succession occur?
It occurs on newly formed, harsh and hostile barren substrates that have not been previously colonised e.g. The lava fields after a volcanic eruption
Describe primary succession.
Pioneer species (usually r strategists) are able to survive the hostile conditions. Over time the lichen degrade the rock and embryonic soil forms. This results in a change in community which further alters the abiotic environment. This process continues through a number of seres, until a final stage the climax community.
What are the two types of climax community?
Climatic climax - Composition of the climax community determined by the climate
Biotic climax - Composition of the climax community determined by a biotic factor
What are the trends in succession?
- The soil develops - increases in depth and proportion of organic content (humus)
- The height and biomass of vegetation increases
- The abiotic environment becomes less hostile
- Communities become more complex
- Increased biodiversity
- Communities in later seres more stable than communities in earlier ones
What can interrupt a succession?
Fire, flooding, wind damage, human interference
Describe secondary succession
Secondary succession does not usually begin with lichens as the soil is already formed, therefore it is much quicker than primary succession. Occurs after an existing ecosystem has been disturbed
