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Lecture 4

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University of British Columbia
BIOL 111
Chin Sun

4.1 Biological Interactions Learning Outcomes 1. Identify different ways organisms interact with one another and the outcomes of those interactions. 2. Distinguish among different types of predation. 3. Interpret results from actual biological studies on species interaction. Read the case study and try to answer the questions associated with it. Readings: Chapter 14: 366-367 (paragraph on habitat fragmentation), 370-378 Both abiotic and biotic factors are important in determining where a species lives. Biotic factors are impacts other living organisms in the same ecological community have on an organism. Examples of biotic factors include what kinds of food an organism eats, what predators preys on it, as well as what species competes with it for limited resources. Under the forest canopy light can be limiting. These two species of ferns spread their fronds to maximize the interception of light. Because they are growing closely together their fronds will overlap. Below the surface of the soil, the root systems of plants seek out nutrients and water. Plant root forms range from fibrous and shallow to individual deep tap roots. The root systems from many individuals will intermingle. Hyenas and vultures both search for and feed on carrion (dead animals). Although in this particular case the hyenas appears not to be affected by the vultures, in other incidents vultures can consume carrion that would otherwise be available to the hyenas had the latter arrived at the food sources in time. Blue mussels and barnacles inhabit the intertidal zone of marine shores. Both species need rock space to attach to. The presence of one species excludes the opportunity for the other species to occupy the same location. Competition: Two species requiring the same limited resources (Inter-specific competition). They may actively interfere with each other or one may exploit the resource before the other competitor can access the resource. Competitive exclusion: The elimination of one species from a habitat due to the presence of another species which can acquire limited resources more successfully or effectively than the former. Garden snail (Pacific sideband snail) grazes vegetation using a file-like radula. Leaf miners are the larvae of insects that eat the chlorophyll -rich inner layer of leaves. Leeches attach to chordates, such as fish and non-hairy animals. They attach with a circular set of jaws to pierce the skin and draw out the blood. Sea gulls effectively hunt for food by searching the shallow waters and attacking live animals such as this sea star. Predation: The process of collecting, harvesting or hunting another living organism (plants, algae, fungi, or animals) for food. Hummingbird feeding on nectar from a thistle flower. In the process the head of the bird is covered with pollen. The hummingbird is critical in the reproduction of the plant. MUTUALISM, another example cleaner fish Lichens are formed from a sandwich of a blue green bacteria or algae between two layers of fungus. Both organisms are dependent on the other for survival. SYMBIOTIC form of MUTUALISM Corals are animals that are encased in hard calcium carbonate shells. They consume other small organisms that they can catch with tentacles but also have algae embedded in their tissues that provide additional sources of energy (sugar) through photosynthesis. SYMBIOTIC form of MUTUALISM Mycorrhizal fungi are associated with the roots of plants. They provide an extensive network of hyphae (thread-like filaments) that absorb, from the soil, water and minerals which they share with plants in exchange for sugars. VERY IMPORTANT ASSOCIATION FOR PLANTS IN MANY SOILS INCLUDING PLANTS OF OUR FORESTS SYMBIOTIC form of MUTUALISM Mutualism: Two different species benefit from interacting with each other. Symbiotic associations: Two species live together and form a distinctive entity. Often the interactions are mutualistic. Small fish like the damselfish often hide within crevices of coral to avoid predation by larger fish. The coral obtains neither benefit nor harm from this interaction. Commensalism One species benefits from the interaction while the other species neither benefit nor suffer. Table of interactions – refer to your text to summarize the types of interactions Type of interaction Effect on Species 1 Effect on Species 2 + + Mutualism predation + - Competition
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