![]() To maintain this equality gains (R + G) must equal losses (D + C). Maximum sustained yield is obtained at less than maximum population density.Ĭoncept of maximum sustainable yield (MSY) is based on identification of "stock" – in practice it is a subset of the entire population, presumed to be representive of the entire "population" Important point here is that maximum sustainable yield not obtained when population is at carrying capacity, although that may be the biggest "one-time" yield. Size and speed of recovery of population size are maximized Þ maximum sustained yieldįrom the logistic equation, optimum population size to harvest in K/2. Harvesting in middle of population considered optimum. Harvest late, slow return (mostly adults) Growth period rapid, mix of adult and juvenile Harvest early, slow return when many juvenile caught So, act of harvesting will affect the rate of population growth.Ĭonsider: Timing of harvest of cohort (e.g. ![]() Results: high per capita increase in fecundity, increased birth rate (via reduced intraspecific competition). However, How the population size is reduced is important is important to how population responses in number over time.Ĭontrolled lab experiments showing density-dependent limitations on population growth also show that when adults are removed population growth is enhance because there is an excess of food for younger stages. Idea: Reducing population size will generally affect life-expectancy and fecundity of organisms. collapse of cod fishery in North Atlantic. Unfortunately human attempts at conscious balancing to insure neither overexploitation nor under exploitation has not had a good record – e.g. density-dependent effects on prey and predator prey intake), while insuring that the prey does not go extinct.įrom examples of our theoretical assessment of predator/prey cycling we found that coexistence is influenced by: The idea of managed harvesting is to maximize the crop yield (i.e. Intrinsically interesting in providing insight into the stability of natural systems.īut, also implication for successful management of human activities involved in exploiting natural resources. Why study the dynamics of predator/prey relationships ? Predation intensity only high when population of predators is low and prey is near carrying capacity ![]() This bending of the predator isocline is referred to as self-limitation.įinally, little cycling observed. Here A) L/V isocline, B) shows that more predators require more prey C) consumption rate is progressively reduced by mutual interference, D) predators limited by something other than food. At higher densities predator mortality rate increases (outside effects). Or, 2) mortality on predator is density-dependent. Could be due to: 1) lower predation efficiency at high predator density because of social interactions (territoriality) leading to interference. Shift to the right at higher predator densities, more prey needed to increase predation density. Now let’s consider changes in the predator isocline: Thus, any perturbation that destablizes the cycle can be restored by immigration. ![]() In this case prey have refuge where predators do not have access. Predator and prey will tend to oscillate only slightly without perturbation. This situation will result in an inward spiraling of the cycle resulting in a dampened cycle. Here predator can exploit prey very efficiently, vectors spiral outward leading to extinction of one or both species. they have a higher efficiency at capturing prey. Predation does not decrease until prey levels are lower, i.e. Populations are rarely in such balance because natural selection favors predators becoming more efficient at capturing prey (especially if predator feeds on a single prey) and prey should be selected to decrease predator efficiency (escape mechanisms, etc.) If the prey line and predation line are symmetrical this will lead to a stable limit cycle – returns to the same point. Density-dependent effects on prey, with predator efficiency at moderate levels. ![]() add some density dependence, we can generate some realism in the model. The amplitude of the oscillation is simply dependent on the where the population starts. As we concluded from last lecture populations the Lotka/Volterra predator prey model results in a predictable manner called neutrally stable cycle. ![]()
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