Ecology: Chapter 1.3 Populations

Framing Questions  What is a population?  What is “carrying capacity” and what factors influence it?  What is the difference between intraspecific competition and interspecific competition?  What are density-dependent factors and density-independent factors?  What does it mean to have an exponential growth curve?  What is a population crash?

A Population  Group of organisms of the same species living in the same place at the same time  Individuals may come and go, but the population can remain the same  Ex: The flamingos of Lake Victoria in Africa.  Assembled for yearly migration.

Carrying capacity: the largest population of a species that an environment can support  4 main factors that determine the carrying capacity: 1. materials and energy: energy, water, carbon, and other essential nutrients 2. food chains: the population size is limited by the size of the populations at lower trophic levels. So, predators are limited by their prey and their food supply. 3. competition: each organism has the same need as any other. They compete for resources such as food, water, mates, space. 3. competition: each organism has the same need as any other. They compete for resources such as food, water, mates, space. 4. density: depending on their size, environment and way of life, different species have different needs for space.

Food Chains In a food web, each organism survives by gaining energy from the trophic level below it. Thus, the size of the populations are continually adjusted by the species’ interactions with both its food supply and its predators. Example: sea otter population near the Aleutian Islands in Alaska herring – seal – killer whale – sea otter – sea urchin – kelp forest – gulls/mussels

A Closer Look at Competition: Two types of competition: 1. intraspecific: among members of the same species ex: competition for mates 2. interspecific: between different species ex: competition for space

A Closer Look at Population Density:  Two types of factors can also limit population sizes. 1. density-dependent factors: these are factors that increase as the population gets bigger and eventually lead to a decrease in the population size by increasing death rate and lowering birth rate. * overcrowding * parasites/disease * aggression amongst members * neglect of offspring

 2. density-independent factors: can limit a population regardless of its original size. * forest fire * flood * volcano * weather

Population Growth  Since all organisms reproduce, populations tend to grow over time  If unlimited resources are present, growth will be exponential  It will proceed very quickly for rapidly reproducing organisms and more slowly for slowly reproducing ones  The curve, however, will always be a “J” curve or an exponential growth curve

Generation# of bacteriatime min 3430min 4845min 5161hr 63275min 76490min min 92562hrs hrs , , ,5364hrs 18131, , , ,048,5765hrs 222,097, ,194, ,388, ,777,2166hrs

Population Growth 2  Resources are never unlimited, though.  As population rises, resources decline.  If the growth is too rapid, resources are rapidly depleted and a population crash can occur  This pattern occurs often with many populations (including humans) Gypsy moth caterpillar

Population Growth 3  More often what happens is that the resources slowly decrease, the growth rate slowly decreases, and they meet.  This point that they oscillate around is the carrying capacity of the environment for that particular organism S - shaped curve

Human Growth Patterns What are the causes of the rapid growth of human populations? What are some possible consequences of this growth pattern? What will our future look like?