1. Interaction in Ecosystems 1. Biotic Interactions 2. Symbiotic Relationships 3. The costs, benefits and consequences of interactions

2. Biotic Interactions Introduction Introduction Predation Predation Grazing Grazing Competition Competition

3. Introduction Abiotic components – conditions and non- living resources in a particular habitat e.g. Biotic components – are the living aspects in an ecosystem e.g.

4. Density independent factors affect population regardless of its size Density dependent factors affect population depending on its size. Usually when the population number is high, these factors act to reduce the population

5. Biotic Interactions Interspecific interactions – between members of different species Intraspecific interactions – between members of the same species

6. Predation Predation is a biotic relationship in which one species kills and eats another (the prey) In nature predator – prey interactions are frequently cyclic The cyclical nature is due to population densities of the predators and the prey This in turn affects the population densities The cycle is actually driven by other interactions (both density dependent and density independent)

7. Draw a predator – prey cycle Describe its features How can predation be useful to prey?

8. Predation cont… Predation creates diversity in an ecosystem, by reducing the dominance of one species and allowing weaker competitors to survive It reduces prey density and therefore density dependent factors in the prey species It drives evolution as prey species adapt to avoid predation, and predators change according to the prey

9. Prey defences Camouflage (crypsis ) – blending with the environment Disruptive colouration – markings to break the body’s outline Other examples include countershading, transparency and colour change Behaviour, such as staying still or choosing a background to hide, helps.

14. Prey defences cont… Warning (aposematic) colouration – adoption of bright colours and patterns by dangerous / inedible species to warn of their danger to others

15. Prey defences cont…. Mullerian mimicry – where one species resembles another and both species are dangerous / inedible to predators

16. Prey defences Batesian mimicry – where one harmless / edible species resembles one that is dangerous / inedible

17. Grazing Grazing is a form of predation, except only part of the prey item is consumed at any one time

18. Grazing cont… In a plant community grazers have two important effects: Maintain species diversity – by keeping dominant grasses under control more delicate species are able to compete more effectively Prevent succession, therefore a climax community is not reached – grazers eat the apical meristems of woodland plants, preventing grow. The basal meristems of grasses are able to withstand grazing. As a result important habitats and niches are often maintained for a number of species

19. Niches What do we understand by the term ‘niche’? A niche is the functional position of an organism in the environment. To describe a niche of an organism detail such as: Habitat Resources obtained (such as food) Periods of time it is active Physical adaptations Must be discussed

20. Niche cont… Fundamental niche – the niche an organism can potentially occupy under ideal conditions Realised niche – the niche an organism actually occupies due to competition

21. Competition Competition is two or more organisms requiring the same resource, which is in short supply Exploitation competition – one species has the ability to exploit the resource more effectively than another species e.g. one species might be faster at obtaining the resource Interference competition – one species prevents another species from obtaining the resource e.g. by territorial behaviour

22. Competitive exclusion principle Gause’s principle No two species with identical (or similar) niches can coexist for indefinite periods of time. Eventually one species will be excluded by the other as a result of interspecific competition

23. Resource Partitioning Resource partitioning – the dividing up of the use of each resource by species specialisation and adaptation Resource partitioning is a consequence of overlapping niches. Each species adapts to exploit different components of a resource

24. Exotic species Species introduced to an ecosystem often out compete native species These species often occupy the same niche as native species, but lack the competitors / predators found in its natural environment. With out these checks and balances the exotic species can dominate the environment

25. Weaker Competitors It is important to ensure the survival of weaker competitors to maintain species diversity Species diversity is important for an ecosystem to respond to changing conditions – in one set of conditions a species may be a weak competitor, but in another set it may be more dominant organism in an ecosystem

26. Learning Activities Read DART pg 21 – 31 Read Monograph pg 15 – 19 Scholar – all of section 3 Find examples of each of the concepts discussed. Barlow’s Brain Buster Questions Worksheets Create a concept map linking ideas of competition and niches