Populations and Communities Flashcards
What is a population?
A group of organisms of the same species living in a particular area at the same time
What factors influence population growth
Birth Rate and Immigration INCREASE
Death Rate and Emigration DECREASE
What are the 4 main stages of population growth?
Lag, Exponential, Stationary and Decline
Describe the Lag phase.
Very slow increase in numbers; bacteria may be activating genes and enzymes for nutrient assimilation
Describe the Exponential phase.
Exponential growth with no restrictions as resources are plentiful and organisms are reproducing at the maximum rate
Describe the Stationary phase.
The birth rate and death rate are in equilibrium. Resources become limiting and toxins start to build up.
Describe the Decline phase.
Resources and nutrients run out and toxic waste accumulates, causing death rate to exceed the birth rate. Competition within the population has increased
What organism is used to show the decline phase in population growth?
Bacteria grown in a nutrient medium in closed conditions (beaker)
How might population grown differ in other species?
Other organisations typically display a sigmoidal (s) shaped growth curve as conditions aren’t closed and the resources are renewable so the curve stops at the stationary phase
What is the biotic potential of a population?
The population is reproducing at its maximum rate under optimum environmental conditions, as seen in the exponential phase
What is environmental resistance?
The environmental restrictions that prevent a population from achieving its biotic potential and maximum growth
List examples of environmental resistance
Lack of nutrients
Accumulation of Waste
Competition
Predation
Climatic factors
What are biotic factors
Living Factors. Due to other organisms such as competition and predation.
What are abiotic factors?
The non-living physical and chemical factors such as nutrients, oxygen availability, light availability, rainfall and temperature.
What is the carrying capacity of a population?
This is the maximum number of a population that the ecosystem can support.
What causes a J-shaped growth curve?
There is a period of very rapid growth. Followed by a crash when nutrient supplies are exhausted and predation/grazing increases
What is competition?
Different organism are competing for the same resource which is in limited supply
What is intraspecific competition?
Competition between members of the same species
What is interspecific competition?
Competition between members of different species.
What is the competitive exclusion principle?
No 2 species can occupy the same ecological niche. One will always lose (the least well adapted one).
Explain the typical predator-prey interactions.
1) As the number of prey increases, there is more food available for predators. So number of predators increase.
2) Prey numbers subsequently decreases, followed by a decrease in predator as there is less food available.
Competition increases between the predator species.
3) As predator numbers decrease, prey numbers increase
4) Predator numbers will always be lower than prey numbers
What is the equation for working out population growth?
Population Growth= (Births - Deaths) + (Immigration - Emigration)
P = (B-D) + (I-E)
What are “r-strategists”
Opportunistic short-lived species with a fast rate of reproduction who typically display a J-shaped growth curve due to rapid growth.
They tend to be small, not good competitors and display little parental care
Are not specialised but can inhabit unstable habitats (good colonisers)
What are “k-strategists”?
Organisms who reproduce slowly, with a longer life-cycle and fewer offspring
Populations tends to remain stable around the carrying capacity (K)
Larger size, good competitors and display parental care
Give examples of + / - interactions.
Predator-Prey interactions and Grazing by herbivores
What is parasitism?
A + / - interaction in which the parasite lives in or on the host. Benefitting from it and causing it harm over a long period.
