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Outline the factors that affect the distribution of plant species, including temperature, water, light, soil pH, salinity and mineral nutrients.
- The distribution of a species is the range of places that it inhabits. The distribution of plants is closely linked to the levels of abiotic factors in the environment. The main abiotic factors are temperature, water, light, soil pH, salinity and mineral nutrients.
- Sometimes the distribution of a plant species shows what conditions a plant prefers.
Explain the factors that affect the distribution of animal species, including temperature, water, breeding sites, food supply and territory.
- The distribution of animal species is affected by both abiotic and biotic factors.
- -Temperature: external temperatures affect all animals, especially those that do not maintain constant internal body temperatures. Extremes of temperature require special adaptations, so only some species can survive them.
- -Water: animals vary in the amount of water that they require. Some animals are aquatic and must have water to live in and at the other extreme some animals including desert rats are adapted to survive in arid areas where they are unlikely ever to drink water.
- - Breeding Sites: all species of animals breed at some stage in their life cycle. Many species need a special type of site and can only live in areas where these sites are available. For example, mosquitoes need stagnant water for egg laying.
- - Food Supply: many animal species are adapted to feed on specific foods and can only live in areas where these foods are obtainable. For example, blue whales feed on krill and so they live in areas of the ocean where krill is abundant.
- -Territory: some species of animal establish and defend territories, either for feeding or breeding. This tends to give the species an even rather than a clumped distribution. Pairs of tawny owls defend a single territory throughout their adult lives.
Describe one method of random sampling, based on quadrat methods, that is used to compare the population size of two plant or two animal species.
- A sample is a part of a population, part of an area or some other whole thing, chosen to illustrate what the whole population, area or other thing is like.
- In a random sample, every individual in a population has an equal chance of being selected.Ramdom sampling of plant populations involves counting numbers in small, randomly located parts of the total area. The sample areas are usually square and are marked out using frames called quadrats.A method for random sampling:
- 1) Mark out gridlines along two edges of the area.
- 2)Use a calculator or tables to generate two random numbers, to use as co-ordinates and place a quadrat on the ground with its corner at these co-ordinates.
- 3)Count how many individuals there are inside the quadrat of the plant population being studied. Repeat Stages 2 and 3 as many times as possible
- 4) Measure the total size of the area occupied by the population, in square metres.
- 5)Calculate the mean number of plants per quadrat. Then calculate the estimated population size using this equation:
- population size=(mean number per quadrat X total area)/(area of each quadrat)
Outline the use of a transect to correlate the distribution of plant or animal species with an abiotic variable.
- An alternative to random sampling is to investigate plant or animal distributions along a line marked out across a site. The line is called a transect.Transects are particularly useful when there is a gradient in an abiotic variable.
- Transects can be used to investigate plant and animal distributions on seashores. The transect should be laid out at right angles to the high tide and low tide lines, so that it follows the gradient in time of inundation by sea water and time of exposure to air.
Explain what is meant by the niche concept, including an organism's spatial habitat, its feeding activities and its interactions with other species.
- Studies of the distributions of organisms and of interactions between organisms show that there are many different ways of existing in an ecosystem. The mode of existence of a species in an ecosystem is its ecological niche. The nich includes:
- Habitat- where the species lives in the ecosystem
- Nutrition- how the species obtains its food
- Relationships-the interactions with other species in the ecosystem.
Outline the following interactions between species, giving two examples of each: competition, herbivory, predation, parasitism and mutualism.
All living organisms are affected by the activities of other living organisms. A situation in which two species affect each other is called an interaction.
- Terrestrial ExampleMarine Example
- Herbivory-a primary consumer feeding on a plant or other producer. The producer's growth affects food availability for the herbivore. The beetle Epitrix atropae feeds only on leaves of Atropa belladonna, often causing severe damage to them. Algae growing on rocks in shallow seas are often heavily grazed.
- Predation- a consumer feeding on another consumer. The numbers and behavior of the prey affect the predator. The Canada lynx is a predator on the Arctic hare. Changes in the numbers of hares are followed by similar changes in the lynx numbers. Bonitos feed on anchovetas in the Pacific Ocean west of Peru. When the anchoveta population crashed in the 1970s starving bonitos were found, with completely empty stomachs.
- Parasitism- a parasite is an organism that live on or in a host and obtains food from it. The host is always harmed by the parasite. The tick Ixodes scapularis is a parasite of deer and of white-footed mice in northeast USA. The tick feeds by sucking blood from its hosts and therefore weakens them. Organisms that cause infectious diseases are all parasites. For example, Sphingomonas bacteria cause a disease in ellipictal star corals on the Florida reef.
- Competition- two species using the same resource compete if the amount of the resource used by each species reduces the amount available to the other species. Trees competing with each other for light, water and minerals. Species of corals competing for food.
- Mutualism- mutualists are members of different species that live together in a close relationship, form which both benefit. The alga supplies foods made by photosynthesis and the fungus absorbs mineral ions. Fish that cleans parasites from the fills and body of larger fish. The cleaner benefits because the parasites that it removes are its food.
Explain the principle of competitive exclusion.
If two species have a similar niche, they will compete in the overlapping parts of the niche. Because they do not compete in other ways, they will usually be able to coexist. However, if two species in an ecosystem have exactly the same niche they will compete in all aspects of their life and one of the two species will inevitable prove to be the superior competitor. This species will cause the disapperance of the other species from the ecosystem.The principle that only one species can occupy a niche in a ecosystem is called the competitive exclusion principle.
Distinguish between fundamental and realized niches.
The niche that a species could occupy is often smaller than the niche that the species actually occupies. These potential and actual niches are called the fundamental niche and the realized niche of the species. Differences between the fundamental and realized niches are due to competition.
Other species prevent a species from occupying part of its fundamental niche by out-competing or by excluding it in some other way.
The fundamental niche of a species is its potential mode of existence, given the adaptations of the species.
The realized niche of a species is its actual mode of existence, which resluts from its adaptations and competition from other species.
Competitive exclusion happens when a species is unable to occupy any part of its fundamental niche in an area, so it has no realized niche in that area.
Ecologists often use a measure called biomass.
Biomass is the total dry mass of organic matter in organisms or ecosystems.
Describe one method for the measurement of biomass of different trophic levels in an ecosystem.