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Life Table Problem • In a population of field mice, 50% of an original cohort of females survive long enough to breed as one year olds. At that time they give birth to three female offspring. 50% of the survivors will live long enough to breed as two year olds. Again they will give birth to three female offspring. Once again 50% of the survivors will live long enough to breed as three year olds. They will again give birth to 3 females. All of the survivors will die once they reach 4 years old due to old age. They will not reproduce as four year olds. What is the net reproductive rate (Ro) for this cohort of field mice? (Hint: you only need to calculate lx and mx to be able to solve for Ro – (Ro = lxmx).) • lx is proportion surviving to age x • mx is number of offspring per survivor at age x
Competition Competition is an interaction between individuals, brought about by a shared requirement for a resource in a limited supply, leading to a reduction in the survivorship, growth, and/or reproduction of the competing individuals
Competition Two key points: • Resource being competed for must be limited in supply 2. Interaction is always negative
Competition Intraspecific competition - competition between members of the same species - thought to be especially strong because members of the same species have the same resource requirements – regulates population size Interspecific competition - competition between members of different species - can be very strong as well – also regulates population size, structures communities, influences natural selection
Mechanisms of Competition 1) exploitation competition (aka resource or scramble) - individuals exert negative influence on each other by using up resources that each need - competition is mediated indirectly through resource depletion - individuals don't need to come into contact to compete 2) interference competition (aka contest competition) - competitors directly interact with each other in the course of seeking a common resource
Competitive Asymmetries • Although competition has negative effects on the population as a whole, some individuals are more negatively effected than others
Territoriality • Territoriality occurs when there is an active interference such that a more or less exclusive area, the territory, is defended against intruders by a recognizable pattern of behavior - individuals or groups are spaced out more than would be expected from a random occupation of suitable habitats
