Table 3.

Number of studies that found positive, negative and neutral effects of abiotic and biotic factors on range limits of North American mammals

Range limit	Factor	Positive	Negative	Neutral	Biotic interactiona	Totalb
High	Abiotic	13	61	1		75
	Biotic	57	18	7	3	85
Low	Abiotic	46	15	11		72
	Biotic	49	12	4	9	74

This table only includes studies that evaluated both abiotic and biotic factors along range limits (n = 138).

^aFew studies coincidentally evaluated biotic interactions (e.g. competition, predation) at broader spatial scales.

^bNote that some studies documented multiple abiotic or biotic factors, which occasionally had opposite signs. For example, if a study indicated that one abiotic variable had a positive effect and another had a strong negative effect, we tallied these as separate records, which increased the total number of studies.