Big biology meets microclimatology: defining thermal niches of ectotherms at landscape scales for conservation planning

Abstract

Temperature profoundly affects ecology, a fact ever more evident as the ability to measure thermal environments increases and global changes alter these environments. The spatial structure of thermalscapes is especially relevant to the distribution and abundance of ectothermic organisms, but the ability to describe biothermal relationships at extents and grains relevant to conservation planning has been limited by small or sparse data sets. Here, we combine a large occurrence database of >23 000 aquatic species surveys with stream microclimate scenarios supported by an equally large temperature database for a 149 000-km mountain stream network to describe thermal relationships for 14 fish and amphibian species. Species occurrence probabilities peaked across a wide range of temperatures (7.0-18.8°C) but distinct warm- or cold-edge distribution boundaries were apparent for all species and represented environments where populations may be most sensitive to thermal changes. Warm-edge boundary temperatures for a native species of conservation concern were used with geospatial data sets and a habitat occupancy model to highlight subsets of the network where conservation measures could benefit local populations by maintaining cool temperatures. Linking that strategic approach to local estimates of habitat impairment remains a key challenge but is also an opportunity to build relationships and develop synergies between the research, management, and regulatory communities. As with any data mining or species distribution modeling exercise, care is required in analysis and interpretation of results, but the use of large biological data sets with accurate microclimate scenarios can provide valuable information about the thermal ecology of many ectotherms and a spatially explicit way of guiding conservation investments.

Freshwater species distributions along thermal gradients

“…Tmax water ) coincides with the findings of Isaak et al (2017), where both the multivariate and univariate (using August stream temperature as explanatory variable) models showed a unimodal response.…”

“…Despite the "overarching importance of thermal regimes to aquatic life" (Isaak et al, 2017), thermal niches of freshwater species are only scarcely studied. For example, Lassalle, Béguer, Beaulaton, and Rochard (2008) found unimodal responses using annual temperature for Acipenser gueldenstaedtii, Acipenser stellatus, Alosa alosa, Alosa tanaica, Vimba vimba, and Osmerus eperlanus, corresponding to our response type categorization for Tmean air .…”

Principle components of thermal regimes in mountain river networks

“…190 Twenty-eight temperature metrics were then calculated to describe aspects of that annual record 191 based on five categories associated with magnitude, variability, frequency, timing, and duration 192 (Table 2). Metrics were similar to those used in previous studies of thermal regimes (Arismendi et 193 al., 2013;Chu et al, 2010;Rivers-Moore et al, 2013;Steel et al, 2016) and in studies assessing the 194 effects of peak summer temperatures on the distribution and abundance of aquatic organisms 195 (Dunham et al, 2003;Huff et al, 2005;Isaak et al, 2017a). Relationships among the thermal 196 metrics were described by conducting PCA on a data matrix in which columns represented the 28 197 metrics and rows were the 226 monitoring sites.…”

“…Water temperature is often monitored because of its importance to aquatic organism phenology 338 (Neuheimer and Taggart, 2007), distributions, and abundance (Isaak et al, 2017a). The majority of 339 previous assessments, however, focus on biothermal relationships associated with magnitude 340 metrics, which has prompted calls to "move beyond the mean" and consider thermal regimes more 341 broadly (Steel et al, 2012;Dillon et al, 2016).…”

Sheltering from the effects of thermal stress

“…Understanding how thermal refugia influence survival of coldwater fish with climate change is becoming an increasingly popular research topic. At present, the assumption is that the presence of refugia per se will increase population survival (Isaac et al ., ). However, in their paper, White et al .…”