The gradualist population theory states that genetic change in a population occurs extremely slowly, over a long period of time. however, the catastrophist theory claims that populations may change drastically over a short period of time, due to catastrophic events like large-scale natural disasters. the theory is a sort of hybrid of the two above, and it contends that long stretches of incremental evolution are interspersed with short periods wherein drastic evolutionary changes occur.

Suggest why placing wheels under a heavy box reduces the neccessary force required to push it along at a constant speed.

What does natural resource management aim at ?

To answer this question, researchers studied populations of the dusky salamander (desmognathus ochrophaeus) living on different mountain ranges in the southern appalachian mountains. the researchers tested the reproductive isolation of pairs of salamander populations by leaving one male and one female together and later checking the females for the presence of sperm. four mating combinations were tested for each pair of populations (a and b)—two within the same population (female a with male a and female b with male b) and two between populations (female a with male b and female b with male a). the proportion of successful matings for each mating combination was measured. for example, when all the matings of a particular combination were successful, the researchers gave it a value of 1; when none of the matings were successful, they gave it a value of 0. then the researchers calculated an index of reproductive isolation that ranged from 0 (no isolation) to 2 (full isolation). the reproductive isolation value for two populations is the sum of the proportion of successful matings of each type within populations (aa + bb) minus the sum of the proportion of successful matings of each type between populations (ab + ba). the table provides data for the geographic distances and reproductive isolation values for 27 pairs of dusky salamander populations.