Listen to part of a lecture in a biology class.
Professor, since we are going to talk about changes in animal populations in the wild, I'd like to ask about something I read in an article online, about how the population size of some animal species can affect other animal species, and how other environmental factors come into play too.
Right. Relationships between animal species in a given ecosystem can get pretty complex.
Because in addition to predator-prey relationships, there are other variables that affect population size.
The article mentioned that populations of predators and their prey might go up rapidly and then decline all of a sudden.
Oh. Yeah! I read about that in my ecology class. It happens in cycles. I think that's called a boom-and-bust cycle. Right?
OK. Well, hold on a second. First I want to go over some key concepts.
Let's say there was a species that had access to plenty of food and ideal conditions.
Under those circumstances, its population would increase exponentially, meaning it would increase at an ever-accelerating pace.
Wow! That sounds a little scary.
Well, it doesn't usually happen. Like you said, a rapid population growth is often followed by a sudden decline.
But we do occasionally see exponential growth in nonnative species when they are transplanted into a new environment.
Um...because they face little competition and have favorable growing conditions.
But for most species, most of the time, resources are finite.
There's only so much available...which leads me to my point.
Every ecosystem has what we call a carrying capacity.
The carrying capacity is the maximum population size of a species that can be sustained by the resources of a particular ecosystem.
Resources are, of course, food, water, and just as important, space.
Although every species has a maximum rate at which the population of that species could increase, assuming ideal conditions for the species in its environment.
There are always going to be environmental factors that limit population growth. This is called environmental resistance.
Environmental resistance is important because it stops populations from growing out of control.
Factors such food supply, predation and disease affect population size, and can change from year to year or season to season.