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Lecture #3 Competition & Niches Unit 9: Community Interactions Competition - Ecological interaction between two or more species that use the same scarce resources. Examples of resources organisms may compete for • Food • Nesting sites • Living space ( territory, home range) • Light • Water • Mates There are two types of competition 1) Intraspecific Competition- Competition that occurs between members of the SAME species. Example- competition for territory between rival wolf packs. 2) Interspecific Competition – Competition that occurs between members of DIFFERENT species. Example- competition for newborn elk calves between wolves, grizzly bear and coyotes Most competitive interactions do not involve fighting. Organisms often times interact only by means of their effects on the abundance of resources. The barn swallow and little brown bat both rely on the same food resource (flying insects.) They hunt at different times though. Why do you think they do this? Answer: Competition between the two species is reduced! One way competition is reduced in nature is by organisms utilizing their own niche. Niche - the functional role (job) of a particular species in an ecosystem. • A niche includes when the organism eats, where it lives, what it eats, the temperature it prefers, when it mates, how it finds a mate, etc. • Every species has its own unique niche. This is why ecosystems tend to be so complex. ** Don’t confuse ‘niche’ with ‘habitat’, which is the PLACE an organism lives. The habitat of a organism is only PART OF its niche. • Sometimes, the niche of some organisms overlap. If the resources that the organisms share are in short supply, this overlap will likely cause competition between the organisms. Example of a Niche - Cape May Warbler The Cape May Warbler is a small insect eating songbird spends its summers in the northeastern United States and Canada. • It nests in spruce trees at the tips of the branches. Fundamental Niche –The entire range of conditions an organism is potentially able to occupy within an ecosystem. The fundamental niche of the Cape May Warbler would include the entire tree on which it lives. Feeding habits The Cape May Warbler feeds at the tops of the trees, even though the insects that it eats are located throughout the tree. • They are only occupying a portion of their fundamental niche. Why? The Cape May Warbler shares the tree that it lives in with other species of birds. • Robert MacArthur (Princeton University) did a study on the feeding habits of 5 species of Warblers. • He found that all five species fed on insects in the same spruce tree at the same time. How do the resources last? Resource Partitioning! Each species occupies a different part of the tree! This reduces competition & allows all five species to coexist. Resource Partitioning for 5 species of warblers The realized niche is part of the fundamental niche. Realized Niche - The part of an organism’s fundamental niche that a species ultimately occupies. • All five species had very similar fundamental niches, yet used different resources. They had different realized niches. What happens if two species are directly competing for the same resources? If two species are competing for the same resource and one is slightly better than the other; the result may be the local extinction of the species less able to obtain resources. Competitive exclusion principle – the local extinction of one species due to competition. Complete competitors cannot coexist Human Impact Human introduction of non-native species to new environments, where some have become invasive, has pushed many native species towards extinction. These ‘introductions’ have been both accidental and intentional depending on the non-native species in question. Introduced (Alien) species- any organism that was brought to an ecosystem where it is not native as the result of human actions Invasive species- A species that takes advantage of an unoccupied niche, or that successfully out-competes native species. • Invasive species have a negative effect on ecosystems or negatively impact humans in some way. Invasive species may grow exponentially if they 1) Lack natural enemies 2) Can occupy an ‘open niche’ 3) Have ‘weedy’ characteristics. Take 2 minutes to summarize what you have learned by explaining how competition may be reduced in nature, what can happen if two species are direct competitors and why introduced species may cause ecosystem damage.