Given the importance of climate in shaping species’ geographic distributions, climate change poses an existential threat to biodiversity. Climate envelope modeling, the predominant approach used to quantify this threat, presumes that individuals in populations respond to climate variability and change according to species-level responses inferred from spatial occurrence data—such that individuals at the cool edge of a species’ distribution should benefit from warming (the “leading edge”), whereas individuals at the warm edge should suffer (the “trailing edge”). Using 1,558 tree-ring time series of an aridland pine ( Pinus edulis ) collected at 977 locations across the species’ distribution, we found that trees everywhere grow less in warmer-than-average and drier-than-average years. Ubiquitous negative temperature sensitivity indicates that individuals across the entire distribution should suffer with warming—the entire distribution is a trailing edge. Species-level responses to spatial climate variation are opposite in sign to individual-scale responses to time-varying climate for approximately half the species’ distribution with respect to temperature and the majority of the species’ distribution with respect to precipitation. These findings, added to evidence from the literature for scale-dependent climate responses in hundreds of species, suggest that correlative, equilibrium-based range forecasts may fail to accurately represent how individuals in populations will be impacted by changing climate. A scale-dependent view of the impact of climate change on biodiversity highlights the transient risk of extinction hidden inside climate envelope forecasts and the importance of evolution in rescuing species from extinction whenever local climate variability and change exceeds individual-scale climate tolerances.

Little is known about insect–plant interactions in high alpine environments. We studied the insect herbivore feeding guild in inflorescences of Cirsium funkiae (Asteraceae), an alpine thistle endemic to the southern Rocky Mountains, USA. We asked whether site (open talus above treeline, mid-elevation wet meadow, or lower-elevation forest edge just below treeline) and plant characteristics affect insect abundance, guild composition, and intensity of herbivory. We dissected flower heads collected at season’s end to quantify fly occurrence and measure herbivory damage. Three tephritid flies—Chaetostomella undosa, Paracantha gentilis, and Terellia occidentalis—strongly dominated the herbivore guild. All three species differed in abundance and composition across habitat sites. Chaetostomella dominated in the high, open talus habitat; Terellia peaked in the mid-elevation meadow site; and Paracantha dominated in the lower forest edge site. While Terellia abundance was strongly associated with flower head diameter, abundances of Paracantha and Chaetostomella were only weakly associated with flower head size, suggesting species-specific flower-head selection. Paracantha and Terellia showed elevated co-occurrence at the mid-elevation alpine meadow site, indicating shared distributional preferences likely related to their occurrence on thistles at lower elevations in this region. Unexpectedly, seed damage was extremely high (91.5–98.5%) across all three sites and highest in the characteristic habitat, open high talus slopes. Despite uniformly high seed damage, the low Forest Edge plants had significantly more viable seeds than did the High site plants (8.2% vs. 1.6%), and the difference was associated with differences in guild composition. These findings demonstrate that tephritid flies dominate floral herbivory on the high alpine Cirsium funkiae, that site differences can shape fly feeding guild structure, and that they have a measurable negative impact on plant seed reproductive success in high alpine environments.

Ecologists have long sought to understand the controls of species’ geographic distributions. Two important hypotheses have been that range limits are determined 1) predominantly by climate or 2) by competition in addition to climate, with competitive interactions dominating where climate is benign. If the first hypothesis is correct, the effect of changing climate on species’ distributions should be adequately predicted by climate-only models. Here, we used demographic range models (DRMs) to evaluate the influence of climate and competition on the geographic distribution of Pinus edulis, a desert pine in the southwestern U.S. We parameterized DRMs with data on 23,426 trees in 1,941 forest inventory plots. Vital rate responses were consistent with the predictions of the second hypothesis: negative effects of warm-dry conditions at low-elevation sites and competition at cool-humid, high-elevation sites. Further, including both climate and competition in the DRM yielded a better fit of DRM-predicted population growth rate to the observed distribution than a climate-only DRM. However, at cool-humid sites, negative effects of competition were too weak to offset positive climate effects, resulting in a mismatch between predicted population growth rate and observed distribution. This result leads us to formulate a new hypothesis: climate has complex influences on species’ distributions through its effects on range-limiting processes at a variety of scales, for example, biotic and disturbance feedbacks at community, ecosystem, landscape, and macrosystem scales. The implications of this complex systems hypothesis are that range dynamics may be poorly predictable from static, climate-only models, and may be characterized by sudden changes in abundance, even distribution collapse, with climate change.