Practice question

Ground squirrels are commonly represented by a Type II survivorship curve because their probability of dying is treated as approximately constant across much of life. On a semilogarithmic survivorship graph, a constant hazard produces a roughly straight decline. Real populations can depart from this ideal when juveniles, dispersers, or old individuals experience different risks, so the classification is a broad empirical approximation. A survivorship curve is built from a cohort life table by plotting the proportion alive at each age. Type I concentrates mortality late, Type II approximates a constant hazard, and Type III concentrates mortality early. These are descriptive models, so a species may shift between them when predators, care, climate, or habitat quality changes. The example should therefore be understood as an application of a general model, with its assumptions kept explicit. Ecological predictions remain conditional on the stated environment, because changing resources, mortality, or interactions can alter the observed demographic pattern.