Practice question

With a weak Allee effect, per-capita growth or fitness improves as density rises from very low levels, yet total population growth remains positive even at the lowest densities. There is no positive critical threshold below which deterministic decline is inevitable. Recovery may be slow, but the population is not forced toward extinction solely by the Allee mechanism. 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.