The formula, r = (b – d) + (i – e), demonstrates that an increase in population size can be attributed to an increase in…

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The equation r = (b − d) + (i − e) shows how population size changes when births, deaths, immigration, and emigration occur.

Option a: home range. While the home range can influence how a population uses space and resources, it does not directly increase the numerical size of the population through the r calculation. It affects spatial dynamics more than the intrinsic rate of increase.

Option b: selection. Natural selection alters the genetic composition over time, not the immediate count of individuals contributing to population size in the current period. It is about allele frequencies, not the birth-death balance in this formula.

Option c: deaths. Since r includes a subtractive term (b − d), an increase in deaths would decrease r rather than increase population size. Higher d reduces population size in the short term.

Option d: competition. Competition can limit population growth by reducing survival or reproduction, potentially lowering b or increasing d, but on its own it does not directly cause an immediate increase in population size as the formula specifies. It tends to constrain growth rather than cause a rise.

Option e: emigration. Emigration reduces population size by moving individuals out, which increases the negative side of the (i − e) component. Therefore, higher emigration would decrease r, not increase it.

Option f: births. Births directly contribute to the (b − d) term; an increase in births raises b, thereby increasing r and the population size. This is exactly how r responds positively to more births.

Option g: resources (food). Availability of resources influences carrying capacity and growth potential, but the instantaneous change in population size is determined by births, deaths, immigration, and emigration. Resources indirectly affect those rates rather than cause a direct, immediate increase in r.

Option h: predators. Predation typically increases mortality or reduces reproduction, which would lower r rather than raise it, so this option would not explain an increase in population size.

BIO 181 (001&002) FALL 2025 FA25: Cumulative Exam 4 covers the most important content from Units 1-4: You can do this!!! : ) [Grade is out of 150/900 pts, the same am't of pts for the active learning "easy points" classwork.]

The formula, r = (b – d) + (i – e), demonstrates that an increase in population size can be attributed to an increase in…

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