9-22-09 - Biology 330 Class Notes 9/22/09 Nt = N0*e^(r*t)...

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Biology 330 – Class Notes – 9/22/09 Nt = N0*e^(r*t) Two consequences: - stable age distribution - infinite growth More commonly used form: dN / Ndt = r*[ (k-N) / k] 1.) Vagaries of the environment 2.) Limit cycle - population does not have fine control over its size * Per capita output is fairly large * The population either overshoots carrying capacity and then collapses 3.) Time lags - if, in the face of abundant resources, sometime in the future the population will increase. The decision to reproduce was made sometime in the past when resources were abundant, NOT based on the resource level when the individual(s) are delivered to the population * This leads to overshooting carrying capacity again 4.) Predator/prey cycles --> increased predator population adds additional predation pressure to the prey --> prey decreases --> predator decreases --> prey increases --> predator increases --> etc. COMBINATIONS OF THESE FACTORS are common! One or more of these factors work in concert Yet, some populations still have a stable-age distribution (which ARE RARE) So we have to ask WHY? Are populations capable of self-regulating?
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If yes, what are the factors involved in self-regulation Ration = (sum of all resources) / N Where N is the size of the population If population is increasing, then the ration per capita will fall If N = K (population size = carrying capacity, there are just enough resources to s o Reproductive activity is the first part of the life cycle that stops o Next, somatic growth will stop o Maintenance is the last activity to stop Intraspecific competition for resources o Scramble competition –> resources are there, every individual has to just grab resources This may lead to a problem of resources scarcity May result in no member getting adequate resources o Contest competition Organisms invent some set of rules and
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9-22-09 - Biology 330 Class Notes 9/22/09 Nt = N0*e^(r*t)...

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