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Biotic Interactions in Ecosystems AH Biology Unit 2 Environmental Biology The Five Laws of Ecology: • Everything is connected to everything else. • Everything has to go somewhere or there is no such place as away. • Everything is always changing. • There is no such thing as a free lunch • Everything has limits. Everything is connected Biotic and Abiotic Interactions • Abiotic - Non living factors – – – – – Temperature Light intensity Soil pH Availability of water Availability of minerals • Biotic – living factors – Competition – Predation – disease Density dependent and density independent factors • Density dependent factors – Effect increases of population density increases – Population level off, then decrease – Example - availability of food • Density independent factors – Effect independent of the size of the population – Example – forest fire Biotic Interactions • Interspecific interactions – Between individuals of different species • Intraspecific interactions – Between individuals of the same species • Which type of interaction is more intense, interspecific or intraspecific? Why? Biotic Interactions • Predation • Grazing • competition predation • Patterns of predator prey interaction – – – – Stable coexistence Cyclical variations Erratic swings Extinction of prey species • Important factors to consider – – – – Carrying capacity of the habitat Reproduction rate of prey Reproduction rate of predator Degree of flexibility of predator to switch prey Cyclical Variations Exercise • Convert the information in the table into a graph to illustrate any patterns that may exist. • Label and number the axes clearly • Decide how to represent the populations of hare and lynx on the same graph. Population numbers in the lynx and snowshoe hare year Population of hare (thousands) Population of Lynx (thousands) 1845 12 22 1850 10 39 1855 63 6 1860 72 21 1865 139 3 1870 3 60 1875 62 4 1880 83 35 1885 120 63 1890 12 10 1895 70 40 1900 10 5 1905 68 43 1910 20 2 1915 60 23 Snowshoe hare and lynx Your graph should look something like this Describe and explain the patterns shown by the graph Role of Predators in maintaining diversity • By removing prey who are strong competitors, weaker competitors can survive • Reduce effect of competitive exclusion • The ecosystem benefits from – Increasing species diversity – Increasing stability – The ability to adapt to environmental change • Examples where removing predators has collapsed an ecosystem – Otters and the sea kelp forests Prey defenses to predators Back • Camouflage • Warning (aposematic)colouration – Red, black and yellow are aposematic colours • Mimicry – Batesian – Mullerian • Watch the video “predators and prey” – Make notes on adaptations of prey to escape from predators. Grazing • A grazer is defined as – Any species that moves from one victim to another, feeding on part of each victim without actually killing it outright • E.g. eating a shoot or a limb • Can increase or decrease species diversity depending on grazing pressure. Grazing of Vegetation Back • Plant species with basal meristems can be grazed without suffering mortality • Plant species with aerial meristems can be eliminated by grazing when the aerial part is removed. • Grassland is often referred to as a plagioclimax, where a diversion deflected succession off course to reach the natural climax community e.g. fire, grazing, mowing Competition • Exploitation competition – Consumer significantly reduces the resource • Interference competition – One species prevents individuals from another from using a resource • Competitive interactions can: – Short term – variations in abundance and distribution – Long term – evolutionary adaptations to improve competitive ability Styles” of Competition • Exploitation competition – occurs when individuals use the same limiting resource or resources, thus depleting the amount available to others. • Interference competition – occurs when individuals interfere with the foraging, survival, or reproduction of others – directly prevent their physical establishment in a portion of a habitat. Niche • The sum of – An organism’s adaptations – The resources it needs – The lifestyle to which it is fitted • Gause’s principle of competitive exclusion – Paramecium aurelia and P. caudatum Experiments – Fundamental niche – Realised niche Principle of Competitive Exclusion • When cultured together Paramecium aurelia has a competitive advantage over P. caudatum for gaining food. Fundamental and Realised Niches Introduction of “exotic species” • Rhododendron ponticum - Scotland – Dense canopy – Leaves contain toxins • Nile Perch – Lake Victoria – Carnivourous fish eating species • Rabbits and Prickly Pear cactus – Australia • Hedgehogs – Outer Hebrides • Rats – New Zealand Importance of survival of weaker species • Species diversity is essential • If environmental conditions change, – The dominant species may no longer be the best adapted and die out – This gives the weaker competitors who are better adapted a chance to increase in number • E.g. extinction of the dinosaur and the emergence of mammals Essay Question – 15 marks Give an account of interactions between predators and their prey Symbiotic relationships AH Biology Unit 2 Environmental Biology Learning Objectives • Describe parasitism as beneficial to one species but harming the other • Explain the relationship between the host and the parasite • Describe modes of parasite transmission • Describe commensalism as beneficial to one species, leaving the other unaffected • Explain commensalistic relationships • Describe mutualism as beneficial to both species • Explain mutualistic relationships Symbiosis • “the living together of two or more different species of organism” • 3 categories of symbiotic relationships – Parasitism – Commensalism – Mutualism Parasitism • Relationship that is beneficial to the parasite but is often damaging to the host species • Ectoparasite – External e.g. ticks, fleas and leeches • Endoparasite – Internal e.g. tapeworm, Trypanosoma, Plasmodium • Obligate parasites – Must live parasitically • Facultative parasites – Does not need to live parasitically – E.g fungi can become saprotrophic if host dies Parasite transmission • Direct contact • Production of resistant stages • Use of vectors – Trypanosoma and the tsetse fly – Plasmodium falciparum and mosquito Host-parasite evolution • Development of a parasitic infestation is countered by host (immune) reactions • The parasite then further adapts • Cyclical evolutionary war – Increasing host specificity the longer the relationship has existed • Parasites may evolve to move from the host to its predator Commensalism • Relationship is beneficial to one species (commensal), the other species is unaffected by the relationship • Examples – Egrets and grazing mammals – Hitchhiking species (energetic consequences?) – Clownfish and sea anemone • It is hard to find strict examples of commensalism as it is unlikely one species in a relationship will be unaffected by the other Mutualism • Both organisms benefit from the interaction. • Co-evolved mutualistic relationships – – – – – – Plants and micro-organisms Protists and fungi (lichens) Terrestrial plants and insects Animals and protists Animals and other animals Interactions in coral reefs • Evolution – Development of inter connected structures, behaviours, physiologies and biochemistries. Essay Question Compare parasitic, commensalistic and mutualistic interactions, using named examples of each. The costs, benefits and consequences of interactions between species AH Biology Unit 2 Environmental Biology Learning objectives • Describe positive, negative and neutral interactions between species • Describe symbiosis as a relationship in which at least one species gains a positive interaction • Explain the effects of host health and environmental factors in changing the balance in symbiotic relationships. • Explain the management of these effects by the human species in promoting human, animal and plant health and the quality of the host environment. • Describe the tolerance and compensation mechanisms for coping with variation in the environmental conditions. Interactions between species Interaction Effects on population density Beneficial to one species (predator) Predation and detrimental to the other (prey) Beneficial to one species (parasite) Parasitism and detrimental to the other (host) One species benefits (the commensal) Commensalism while the other is largely unaffected The interaction is beneficial to both Mutualism species The interaction is detrimental to both Competition organisms Host health and environmental factors • The delicate balance that is the consequence of most symbiotic relationships is affected by both biotic (host health) and external factors (environmental conditions). • Host health – Healthy hosts are able to tolerate parasites presence – Influenced and managed by the use of pesticides or drugs that alter the balance of the parasitic relationship in favour of host species. • Environmental conditions – E.g. coral bleaching • Competition – negative interaction for both species • Symbiosis – at least one species gains a positive interaction Interactions with the environment • All organisms must be able to make internal adjustments in response to external changes in conditions – External – constant flux – Internal – range that must not be exceeded. • Organisms responses – Resist or tolerate – Regulation (homeostasis) – Avoidance / migration Behavioural responses • Changes in an organism’s behaviour which help them to survive changes in their environment. • Examples – Desert mammals • Nocturnal • Live in burrows during day – Hibernation or migration to avoid low temperatures Physiological responses • Changes in a way an organism’s body functions to enable it to survive in changing circumstances. • Organism can show a certain tolerance to its environment • Homeostasis Essay question Give an account of the costs, benefits and consequences of interactions between species, including human involvement.