Breeding success at the range margin of a desert species: implications for a climate‐induced elevational shift

Abstract

If the breeding range of a species is limited by biotic or abiotic environmental factors that depress breeding success at the range margin, then range expansion is expected when those limiting factors are alleviated. Over a three‐year period, we measured breeding success of a desert species, black‐throated sparrow Amphispiza bilineata, along a steep elevation gradient between the Peninsular Mountains and Colorado Desert (San Diego County, California) that is undergoing a warming trend. We compared breeding success at geographically marginal locations (higher‐elevation chaparral sites) to more central locations (lower‐elevation desert scrub sites) only a short distance apart. Breeding success was measured at the nest level, territory level, and population level. At each level measured, breeding success tended to be greater at higher‐elevation chaparral sites at the distribution margin compared to lower‐elevation sites where the bird was more common. Black‐throated sparrows had 100% reproductive failure at lower‐elevation sites during the two driest years of our study (2006–2007), but did relatively well at higher‐elevation sites. Only in a wetter year (2008) was breeding success improved at lower‐elevation sites. Surprisingly, there was no evidence of an upward elevational shift in distribution over a 26‐year period despite a clear warming trend and drier conditions. Greater territory density at lower‐elevation sites with reproductive failure during dry years suggests the possibility of an ecological trap in this system, which could prevent or delay climate‐induced range shifts. A common presumption has been that desert species will undergo relatively mild negative impacts due to a warming climate, but it is possible that some desert species are already at or near their temperature and aridity tolerance limits within their current range and shifts may not always be possible.

Spatial structure and dynamics of breeding bird populations at a distribution margin, southern California

“…In this system, desert scrub species have been shown to have increased reproductive success at higher elevations at distribution margins compared with lower elevations where the birds are more common, at least during dry years (Hargrove, 2010), which seems to support the tendency towards upward shifts. However, not all species shifted upwards, and some species may have a persistent preference for desert scrub habitat despite lower reproductive success (Hargrove & Rotenberry, 2011). Thus, distributional correlations with climate may be less sensitive than local-scale reproductive success in predicting distributional shifts, and, furthermore, it is possible that biotic associations can override or delay climate-induced range shifts, particularly if habitat features such as vegetation composition and structure lag behind climate change.…”

Spatially heterogeneous impact of climate change on small mammals of montane California

“…Precipitation changes were more spatially heterogeneous, with spatial covariation increasing across the northern part of the state and decreasing across the southern part [27,28]. Elevational ranges of species in California over this period have shifted heterogeneously, including species moving upslope, downslope or not at all [13,14,29]. Heterogeneity in movements of species has been partly explained by incorporating local-scale measures of climatic change for both temperature and precipitation [14,30]; increases in the former usually favour upslope shifts, while increases in the latter typically favour downslope movements.…”

Range-Wide Latitudinal and Elevational Temperature Gradients for the World's Terrestrial Birds: Implications under Global Climate Change

“…This variation in ecological traits across latitudinal or elevational gradients can in turn affect reproductive potential and rates of population growth, especially at range limits [19], [20]. Under climate change, the structure of latitudinal and elevational temperature gradients can be modified, affecting population growth rates, especially at the leading and trailing edge of the gradient within species' ranges [21], [22].…”