G5: Population Ecology

Distinguish between r-strategies and K-strategies.

• An r-strategy involves investing more resources into producing many offspring, having a short life span, early maturity, reproducing only once and having a small body size.

• A K-strategy involves investing more resources into development and long-term survival. This involves a longer life span and late maturity, and is more likely to involve parental care, the production of few offspring, and reproducing more than once.

Homework 1

• List 5 r and 5 K-strategists

Discuss the environmental conditions that favor either r-strategies or K-strategies.

• In a predictable environment, in order to maximize fitness, it pays to invest resources in long-term development and long life (K-strategy).

• In an unstable environment, it is better to produce as many offspring as quickly as possible (r-strategy).

• Of concern is that ecological disruption favours r-strategists such as pathogens and pest species.

Describe one technique used to estimate the population size of an animal species based on a capture–mark–release–recapture method.

• Various mark-and-recapture methods exist. Knowledge of the Lincoln index (which involves one mark–release–recapture cycle) is required, as follows: n1 x n2

• Population Size = ------------------• n3• where n 1 = number of individuals initially caught,

marked and released, n 2 = total number of individuals caught in the second sample, and n 3 = number of marked individuals in the second sample.

Describe the methods used to estimate the size of commercial fish stocks.

• Determine the distribution of the ages of caught fish(extraction and examination of ear bones – otoliths; increasing # of rings associated w age)

• The greater the fraction of older fish the healthier the population

Outline the concept of maximum sustainable yield in the conservation of fish stocks.

• The concept of MSY is based on a largest yield that can be taken from a species' stock over an indefinite period of time. Assuming the population is of logistic growth, the MSY should be exactly half the carrying capacity of a species, when population growth is highest.

Discuss international measures that would promote the conservation of fish.

• International measures that could be taken are:– monitoring of stocks and of reproduction rates,– quotas for catches of species with low stocks,– moratoria on catching endangered species,– minimum net sizes, so that immature fish are not caught,– banning of drift nets, which catch many different species

of fish indiscriminately.