An animal developed toxicity. Would you expect it to have a higher population or lower? Explain

Answer 1

The simple answer might be that once toxicity evolves, the animal will have lower mortality (a lower death rate), so population sizes will be larger (population growth rate = birth rate + immigration rate - death rate - emigration rate). But this is overly simplistic. A more realistic answer is that it depends on a variety of other factors that are not specified in the question. A few are discussed below.

First, there are often tradeoffs among traits. While a lower predation risk may result in a lower death rate, being toxic may entail costs, such as energetic costs, that reduce the energy available for reproduction. The greater the costs of toxicity, the lower the birth rate and thus the slower the population growth rate. Prior to the evolution of toxicity, the animal might have had a greater population growth rate, despite the fact that it was commonly eaten by predators, because it didn't pay the costs of chemical defenses and thus had a much higher reproductive rate.

Second, depending upon the resources required by the toxic animal, the carrying capacity of the environment may be lower or higher than it was prior to the evolution of toxicity. Many toxic animals, for example, obtain their toxins from plants. If plants with the necessary toxins are rare, the carrying capacity may be low, meaning the population sizes will be low. Or, conversely, if plants with the necessary toxins are common, the carrying capacity may be high.

There are other complications.