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Topic+7+Spacing,+Mating+Ecology

# Topic+7+Spacing,+Mating+Ecology - Topic 7 Spacing and...

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Topic 7. Spacing and Mating ecology Topic 7A. Spacing Ecology and Territoriality I. How do organisms space themselves over the landscape? Assume sessile (= fixed in location) individuals (trees, corals) and plot locations: A. random. B. clumped. Maybe habitat restricted, maybe benefit to group. Can tell by various statistical methods. C. overdispersed (= widely and regularly spaced). Like trees in an orchard. Also can be true in nature, especially when resource is scarce, e.g. water in desert. Can be reinforced by chemical inhibitors, as in sagebrush ( Artemisia ), or sessile marine animals. II. How can we characterize a mobile organism’s use of space? A. Home range. Def. for a single animal, the area it frequents during normal activities. To determine this, directly observe the organism, or use a transmitter or some other electronic device. Get points on map separated in time. How to convert to an area? The minimum-convex-polygon (MCP) method: Compute the smallest polygon with (i) all points on boundary or within, and (ii) no interior angle greater than 180 degrees. Instructor will draw in class for this space to illustrate the MCP. Huge drawback: sample-size dependent. Also points not independent in time if interval between successive observations too short. So could easily be an underestimate.

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B. Territory 1. Defended area; if defense very good, an exclusive area. 2. Note that territories space individuals out. Can take average location and points will be overdispersed. Slide of song sparrow. C. Relation of home range and territory: Home range need not be territory. If entire home range is defended, it is a territory. But home ranges may overlap (no defense, partial defense) III. Territories mostly occur in vertebrates. A . birds common Slide still showing B. also fish, lizards C. also insects sometimes, e.g. dragonflies & damselflies, insect order Odonata Slide 2 ft wingspan in Carboniferous Period.
IV. Why defend territories? = why is territorial defense sometimes favored by natural selection? Food supply the commonest reason, but mating is another reason for many species.

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Topic+7+Spacing,+Mating+Ecology - Topic 7 Spacing and...

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