Populations Flashcards
What is an ecosystem?
The inter-relationships between living organisms and their non-living surroundings (referred to as abiotic). It is a unit which contains all the organisms living in a particular area as well as the abiotic factors of the environment.
What is a community
All of the living organisms in an ecosystem. This means all of the populations of different organisms living in the same place at the same time.
What is a population?
A group of individuals of one species which live in a certain defined area/habitat.
E.g frogs in a pond
What is an environment?
The conditions which surround an organism. These conditions can be divided into two main groups- abiotic factors and biotic factors.
What is a habitat?
The place where a community of organisms live
E.g woodland, seashore, pond
What are abiotic factors?
Physical and chemical factors which affect the organisms’ ability to survive within the habitat e.g temperature, pH, light intensity
What are biotic factors?
Factors associated with the other animals or plants sharing the same habitat e.g competition for food, nests, predations etc.
Advantages of biological control agents
- Do not have a negative effect on biodiversity
- The development of pests’ resistance is unlikely
- Biological control agents reproduce and so are self-perpetuating over time
- Biological control agents are more likely to target ONLY the pest species (they are specific)
Disadvantages of biological control agents
- Control is slower
- It will not exterminate the pest
- Research to ensure that the program will be successful (I.e. control agents doesn’t become a pest species) can be expensive.
- Often unpredictable
- Control agents cannot cope with sudden changes in pest numbers.
What is a pest?
A species that competes with or causes damage to valuable/commercial crops, causing economic damage.
What is biological control (of pest species)?
This involves deliberately introducing a natural predator, competitor, parasite or pathogen that will target and cause harm to the pest species.
What is the aim of biological control?
To reduce the pest numbers to a point below the economic damage threshold. In most cases, the pest is not completely eliminated.
List some properties of an organism used for the efficient biological control of a pest.
- Highly species specific
- Reproduce rapidly
- Have a good searching capacity (to keep the pest at low numbers)
- Long term
- Does not cause environmental damage
What groups of organisms can be used for biological control?
- Insect parasites
- Pathogens
- Predators
What is the downside of using predators as a biological control?
They are carnivorous, and so once they have reduced the original pest to a low level, they may in turn become a pest and attack other species.
What are some of the reasons for the “Lag Phase” in a population growth curve?
- Nutrient assimilation
- Larval development
- Gestation period
- Egg production
What does the term “carrying capacity” mean?
The maximum number that the environment can support.
What does the term “biotic potential” mean?
The reproductive capacity of a population under optimum environmental conditions.
During the “Exponential/log Phase” of a population growth curve, by what value do the numbers increase by?
Hint- designated “r”
The intrinsic rate of natural increase
What effect does temperature have on a population?
- Temperature is NOT a resource
- Temperature will determine the metabolic rate in organisms and so the rate at which they develop.
- A higher temperature will not influence the size of the maximum population (it’s carrying capacity)- this is determined by resources e.g available nutrients.
- Height of stationary phase stays the same on the graph
List some features of an r-selected species
- Small size
- Weak competitors
- Large number of offspring
- Require little parental care
- Unstable habitat
- Population density is highly variable and often over shoots K - “boom-and-bust” dynamics.
- High dispersal- migrate readily & recolonise easily
List some features of a K-selected species
- Large size
- Strong competitors
- Small number of offspring
- Stable habitat
- Require considerable parental care
- Low dispersal- recolonisation is uncommon
- Population density is less variable- usually near K
- Reproduce slowly
What is the equation for change in population density?
(Births-Deaths) + (Immigration-Emigration)
What is the difference between “parasitism” and “predation”?
- In parasitism, the host is killed very slowly. Whereas in predation the prey is killed immediately.
- Predators will kill their prey to obtain nourishment, parasites do not.
What is the competitive exclusion principal?
Two species cannot share the same niche without one species being eliminated.
“Two species cannot share the same niche without one species being eliminated”
What is this principle called?
Competitive exclusion principle
If both species benefit from an interaction, their interaction is called…
Mutualism
- The interaction may be necessary for both
- Each species gives and takes from the other species
- Example- bacteria living in the human large intestine gain food from us and provide us with vitamins
Describe the predator-prey relationship.
The predator-prey relationship is one that oscillates.
- Low numbers of predators allow prey numbers to increase.
- High numbers of prey allow predator numbers to increase.
- High numbers of predators cause a decrease in prey numbers. Decrease in food= intra-specific competition increases
- Low numbers of prey cause a decrease in predator numbers
Cycle continues
When does competition between two species occur?
When two species require a common resource which is in limited supply.
What are the characteristics of competition?
- The species may share the same niche, or exhibit niche overlap.
- Both species do less well when competing for the resource.
- One species is eventually eliminated from the habitat.
- The winner may utilise the resources more efficiently or has an adaptive feature allowing it to compete more effectively causing it to be more successful.
- The outcome of competition may well be determined by the environmental conditions.
What factors influence the carrying capacity of a population?
•Food supply •Habitat •Competition •Predation •Disease 
Define the term environmental resistance
Factors which prevent a population reaching its biotic potential.
For example- lack of resources
List some examples of environmental resistance
- shortage of food or prey
- predation or parasitism
- disease
- accumulation of waste
- shortage of space or territory
Give three +/- population interactions.
- Grazing
- Parasitism
- Predation
