3. Population Dynamics: the changes that occur in populations are a result of many factors operating simultaneously. The study of population dynamics is a key tool in wildlife management that utilizes the following concepts.
a. S-Curve: a species population will grow in a characteristic way. The plot of this growth has four distinct phases.
i. Establishment: a population disperses to a vacant habitat
ii. Rapid Growth: a population increases slowly at first and then rapidly multiplies, taking advantage of unlimited resources.
iii. Growth Deceleration: growth slows as resources become limiting.
iv. Equilibrium: a population becomes well established and other factors such as competition and predation limit their size. Population fluctuations and other ‘noise’ decline.
b. Carrying Capacity: the number of organisms a habitat can support. The carrying capacity is a consequence of density dependent factors; food, cover, and breeding sites become limited and population growth is inhibited; birth and death rates fluctuate but the overall growth rate becomes constant.
c. Maximum Sustainable Yield: the greatest yield possible that does not harm a populations long term survival by upsetting the ecological balance of an ecosystem. This is generally achieved between the explosion and decelerating phase of an S-Curve. If a population is harvested below fifty percent of its carrying capacity, it may not recover.
d. Irruptive Populations: a sudden increase in population size may occur after a period of unusually favorable weather that provides food or exceptional offspring survival. A population may exceed it’s carrying capacity and then plummet dramatically. This often results in severe damage to an ecosystem.
e. Cyclic Populations: Typically 3-4 year cycles of population peaks followed by subsequent scarcity. Fluctuations occur proportionally to changes in food supply, cover availability, or exposure to predators.