Population Ecology Continued…

What Limits Population Growth? No population can grow indefinitely! Something stops them. Those things are Resources (light, water, food, nutrients) and Competitors. The intrinsic rate of increase (r) is the rate at which populations would grow if it had unlimited resources. All those factors that limit growth are environmental factors, we call this environmental resistance. Environmental resistance and biotic potential (Populations capacity for growth vary) determine the Carrying Capacity of a population.

What is the difference between Exponential and Logistic Population Growth? Exponential: Looks like a “J” and the growth of a population accelerates extremely quick. Logistic: Looks like a “S” and the growth may look exponential at first but slows down and becomes constant.

What happens if a population exceeds carrying capacity? The population may go from exponential to logistic, but NOT smoothly. If this happens the population may overshoot and use up too many resources which can result in deaths/diebacks. Sometimes overshooting past the carrying capacity can lead to an environment having a smaller carrying capacity in the future. A good example is overgrazing. If cattle overgraze in an area it may destroy the roots of the grasslands for acres. If the roots are gone that precious topsoil with all the nutrients may get washed away from heavy rains or blown away from winds. If that happens nothing will grow in that region which can reduce carrying capacity for the cattle. Before overgrazing the carrying capacity of an ecosystem is 1000 cows on 10 acres of land. After overgrazing the carrying capacity of an ecosystem can be 500 cows on 10 acres of land.

Do Predators Control Population Sizes? As a population increase its natural predators will have more prey to hunt. An increase in nutrients/resources leads to an increase in population size for the predators. If there are too many predators the population of prey can fall. Once the population of prey fall so will the predator population. This can create a pattern or cycle in populations over time! The most well known is the Lynx and the Hare.

How do Species Reproduce? Asexual Reproduction: Offspring are exact genetic copies of parent. Sexual Reproduction: Offspring are a combination of the mother and father. DNA is similar but not the same. What are some PROS and CONS of sexual reproduction?

PROS VS CONS Negatives of Sex? Positives of Sex? Males don’t give birth. (great for men, but to increase a population you have to have at least 3 children). Higher genetic diversity. (we aren't exact copies of our parents or other people which means we are less susceptible to diseases and environmental issues). Increased chances of genetic errors or mutations. (during development the cells are more likely to replicate incorrectly leading to genetic issues). Food, Care, and Protection of young in clumped populations. (Usually males would go look for food for the females and young as well as protect them from harm. Increasing survival chances). Courtship and mating takes time and energy. (some animals will dance for days just to mate. In humans we don’t usually mate for 18 years or so and we spend quite some time dating before sex occurs).

STOP