Would it surprise you to hear the environment puts up resistance? But to what? And how? Here, you’ll learn what environmental resistance is and how it affects population growth.
What Is Environmental Resistance?
Have you ever heard the expression that some efforts are like trying to push a boulder uphill? In biology, environmental resistance is a little bit like the hill and the boulder is a population of organisms.
If you were trying to push a boulder on flat ground or downhill, it would be much easier. Same with pushing a pebble or piece of gravel uphill. It would be no big deal. But a boulder going uphill is a different story.
Environmental resistance factors are all the things that keep a population of organisms from endlessly increasing. They lower the chances for reproduction, affect the health of organisms, and raise the death rate in the population. Environmental resistance factors include factors that are biotic (living) and abiotic (non-living). Biotic factors are things like predation, parasitism, lack of food, competition with other organisms and disease. Abiotic factors include drought, fire, temperature, and even the wrong amount of sunshine. You can see how all these things, biotic and abiotic, would become an uphill battle to your boulder-pushing.
The Push and Pull of Populations
While environmental resistance acts like a hill pushing back against population growth, biotic potential is what urges a population to grow. Biotic potential has to do with how well a species can survive, including how well adapted it is to the environment and its rate of reproduction. Some species produce a lot of young very often (while others produce fewer babies less often), but invest a lot of energy raising and protecting them.
So, while the biotic potential of a species causes the population to increase, environmental resistance keeps it from increasing relentlessly.When the population is small, environmental resistance factors are, not as big of a factor. There may be plenty of resources around so the population can keep growing quickly. It’s kind of like pushing a piece of gravel uphill rather than a boulder.
But, as competition get stiffer and resources start to become limited, population growth starts to slow.When the birthrate and death rate are the same, the population has reached equilibrium. For that population, in that particular environment, the carrying capacity has been reached. No more individuals can fit. This equilibrium is usually fleeting.
Birthrates and death rates will bounce around. This is quite obvious in my own neighborhood, where there have been years when you can’t drive down the street without five or six rabbits darting across and other years where there are none. Coyotes, more competition for food, drought, and cars tend to knock back the rabbit population when the rabbits work towards their well-known biotic potential.Environmental resistance factors have different amounts of pushback on a population. If the environmental resistance factor comes in the form of a sudden catastrophe, like a fire or flood, population numbers can crash. If the environmental resistance factor is a renewable resource, like food, population growth eventually slows down when the carrying capacity is reached, rather than crashing.
Humans are not immune to environmental resistance factors. While we’ve invented machines to push boulders uphill, the evening news makes it obvious that hills still exist. Floods, fire, drought, hurricanes, starvation, competition, and disease will likely always get in the way of our biotic potential.
Environmental resistance factors are things that limit the growth of a population. They include biotic factors – like predators, disease, competition, and lack of food – as well as abiotic factors – like fire, flood, and drought.
The biotic potential of a population is how well a species is able to survive. Their adaptations to the environment and their reproduction rate affect the biotic potential of that species. Carrying capacity is the largest population of individuals a particular environment can support, although even when the population reaches the carrying capacity of an area, the equilibrium between the birth rate and the death rate of a species isn’t usually steady for long. Some environmental resistance factors, like fires and floods, cause sudden crashes in a population. Others cause a slow wind down in population growth.