Practice question

This item cannot be evaluated rigorously because the symbols b1, b2, d1, and d2 are not defined and no referenced graph or equations are supplied. The key labels the statement that both b1 and b2 are density-dependent as false, presumably assuming b1 is density-independent and b2 density-dependent. That conclusion depends entirely on missing definitions, so it should not be treated as a general ecological law. Density dependence is identified by a change in a per-capita demographic rate as abundance changes. Negative density dependence restrains growth and can regulate abundance; positive density dependence can make sparse populations vulnerable. A factor can affect population size without regulating it if its impact does not create a restoring response to density. A useful check is to ask what happens at the biological extremes and whether the proposed mechanism still makes sense. Interpreting the example at the appropriate population scale keeps the causal mechanism distinct from a simple correlation or an absolute rule.