Wildlife, Fisheries and Endangered Species Chapter 14 Wildlife, Fisheries and Endangered Species

Why Preserve Endangered Species? Justifications: Utilitarian Ecological Aesthetic Moral Cultural

Traditional Single-Species Wildlife Management Assumptions (Logistic Growth Curve) Maximum Sustainable Yield (MSY): The population size that yielded maximum production Minimal Viable Population: The goal for a threatened or endangered species

The Logistic Growth Curve Def: The S-shaped growth curve that is generated by the logistic growth equation In the logistic, a small population grows rapidly, but the growth rate slows down, and the population eventually reaches a constant size Logistic Carrying Capacity: The population size at which birth equals deaths and there is no net change in the population (number sufficient for resources available Optimum Sustainable Population: The population level that results in an optimum sustainable yield. The level is in some way best for the population, its ecological community, its ecosystem or the biosphere (sustained indefinitely)

More on the Logistic Growth Curve: Small populations grow exponentially. Competition slows the growth rate. The greater the number of individuals, the greater the competition and slower growth rate. Will eventually reach the “logistic carrying capacity”. Number of individuals is sufficient for resources available Births equals deaths per unit time A population can be described simply by its total number, so all individuals are equal. The environment is assumed to be constant.

Carrying Capacity A logistic population is stable in terms of its carrying capacity; it will return to that number after a disturbance. Carrying Capacity Logistic carrying capacity Optimum sustainable population

Problems… Carrying capacity varies with changes in the environment. Requires accurate counts each year. Requires the environment not vary or, if it does, that it vary in a way that does not affect the population.

Classic Cases of Wildlife Management or Mismanagement The American Grisly Bear The American Bison A common goal in wildlife conservation is to “restore” the abundance of a species Adequate information of the abundance of a species is very rare

Four Principles of Wildlife Conservation Safety factor for population size which allows for limitations Concern with the entire community and renewable resources Ecosystem maintenance Continual monitoring, analysis and assessment

Improved Approaches to Wildlife Management Goal: achieve a minimum viable population in a minimum viable habitat Time Series and Historical Range of Variation - Time Series: an estimate of a population over a number of years - Historical Range of Variation: the known range of abundances of a population over some past time interval Age Structure as Useful Information Harvests as an Estimate of Numbers Catch per Unit Effort: estimates previous animal abundance. Assumes same effort by hunters.

Fisheries The Decline of Fish Populations Can Fishing Ever Be Sustainable? Past experience suggests that economically beneficial sustainability is unlikely for most wild populations MSY: past management; often resulted in overfishing

The Current Status of Endangered Species Red List Endangered vs. Threatened How a Species Becomes Endangered or Extinct Local Extinction: Occurs when a species disappears from a part of its range Global Extinction: Occurs when a species cannot be found anywhere Survival of an endangered species Depends strongly on the size of the ecological island the species lives on

Causes of Extinction Population Risk Environmental Risk Natural Catastrophe Genetic Risk

How People Cause Extinctions and Biological Diversity Intentional hunting or harvesting Disrupting or eliminating habitats Introducing exotic species Creating pollution

Trawling on Coral Reefs Coral reef in the Florida Keys National Marine Sanctuary Before and after trawling Essentially nothing is left after the trawl has scraped the reef

The Good News Many species have been successfully restored to an abundance Success is achieved when the habitat is restored to conditions required by a species The conservation of wildlife offers great rewards of long-standing and deep measure to people