Evaluating the effects of climate change on biological communities: Integrating historical science with biogeography and physiology

Changes in the abundance of macroinvertebrate species documented in a rocky intertidal community, between surveys in 1931--33 and 1993--1996 are consistent with the predicted effects of recent climate warming. I found that changes were related to geographic ranges of species. Most southern species (10 of 11) increased in abundance, while most northern species (5 of 7) decreased. Cosmopolitan species showed no clear trend, with 12 increasing and 16 decreasing. Shoreline ocean temperature during this 60 year period, especially in the years immediately preceding the current study. The importance of range categories to this study suggested that patterns of abundance distribution within a species' range may be important determinants of how a species responds to climate change. In a review of literature, I found few empirical studies that support the generally assumed idea that species' abundances should be greatest at the center of their ranges and decline toward the edges. Moreover, studies of this pattern are often misleading because they fail to account for the much greater area of the range edge in 2-dimensional species' ranges. This problem is potentially avoided if the study species inhabits a range that is approximately 1-dimensional, as is the case with marine intertidal species. I examined patterns of abundance distribution in 12 intertidal invertebrate species sampled throughout their ranges along the Pacific coast of North America. I found that most species had some sites of very high abundance near the edge of their ranges and few species had highest abundances near their range centers. Because physiological condition may be related to abundance within a species' range as well as the determinants of range boundaries, I examined patterns in heat shock protein (hsp) 70 in 3 intertidal invertebrate species sampled at several locations across their range. Species showed elevated levels of hsp70 in the southern parts of their ranges, where ocean temperatures are relatively warmer and in northern Oregon, where the number of daytime low tides peaks in summer. The data on hsp concentration are considered preliminary in light of our incomplete understanding of organisms' heat shock response.