Tropical mountain passes are out of reach – but not for arboreal species

Scheffers, Brett R.; Williams, Stephen E.

doi:10.1002/fee.1764

Cited by 22 publications

(31 citation statements)

References 68 publications

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“…Our findings contribute to reconcile contrasted views about the relative importance of two distinct scales of climate variability in shaping patterns of subterranean biodiversity (Zagmajster et al, ), a topic that has been recently discussed also in surface ecosystems (Scheffers et al, ; Scheffers & Williams, ). Using correlative methods, Zagmajster et al () and Eme et al () showed that long‐term temperature variability accounted for a substantial variation in range size of groundwater crustaceans across Europe.…”

Section: Discussionsupporting

confidence: 83%

Section: Climatic Controls On Subterranean Biodiversity Patternssupporting

confidence: 76%

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Extending Janzen’s hypothesis to temperate regions: A test using subterranean ecosystems

et al. 2019

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Janzen’s hypothesis (1967; American Naturalist) predicts that tropical habitats with reduced thermal seasonality would select for species with narrow thermal tolerance, thereby limiting dispersal among sites of different elevations showing little overlap in temperature. These predictions have so far been tested by confronting tropical and temperate mountain communities, leaving unresolved the question of their generalization to habitats with low thermal seasonality outside the tropics. We provide the first extension of Janzen’s hypothesis to temperate habitats, by testing for differences in thermal tolerance and elevational range among congeneric alpine spiders (Araneae: Linyphiidae: Troglohyphantes) occurring along a steep gradient of decreasing thermal seasonality with increasing cave depth. Using species from the same temperate region rather than from distinct biogeographic regions avoids confounding the effects of short‐ and long‐term climatic variability on thermal tolerance and elevational range extent. Following Jansen’s assumptions, we predicted that cave habitats with low thermal seasonality would select for narrow thermal tolerance. Also, specialized subterranean species would exhibit both narrower elevational range extents and smaller realized thermal niche breadths. Initially, we showed that thermal seasonality and the overlap in temperature across caves were considerably lower in deep than in shallow cave habitats. Then, we measured thermal tolerance and used morphological traits to quantify the degree of specialization to subterranean life of 11 spider species. We found that thermal tolerance decreased with increasing subterranean specialization. Deep subterranean species reached their critical temperature at 1–4°C above their habitat temperature, whereas shallow subterranean species withstood a twofold larger temperature increase. At last, we demonstrated that a species’ elevational range extent and the variation of temperature encountered across its range decreased with increasing specialization to deep subterranean life. Our integrative work, being grounded in organismal and habitat measures, represents the first generalization of Janzen’s framework to caves and provides a conceptual framework to disentangle the effect of long‐term climate variability on subterranean biodiversity patterns. Extending Janzen’s thoughts to a broader range of ecosystems is key to understanding how the ecological specialization–dispersal trade‐off may constrain the response of species to climate change. A free Plain Language Summary can be found within the Supporting Information of this article.

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Section: Discussionsupporting

confidence: 83%

Section: Climatic Controls On Subterranean Biodiversity Patternssupporting

confidence: 76%

Extending Janzen’s hypothesis to temperate regions: A test using subterranean ecosystems

et al. 2019

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“…Our hypothesis is derived from the same underlying physiological principle; species are adapted to temperatures normally encountered in their temporal and geographical habitat or microhabitat (Janzen, ). Similar hypothesis has been proposed for a vertical climatic gradient in rain forest (Scheffers & Williams, ), and circadian climatic gradients with contrasting daytime and night‐time thermal variability (Muñoz & Bodensteiner, ).…”

Section: Introductionsupporting

confidence: 76%

“…Local climatic fluctuations, such as habitat variation, may also explain the absence of the expected divergence in dispersal capacity (see Chan et al., ). It is possible that horizontal movements of organisms will represent a climate sorting process allowing organisms to increase resilience to climatic changes under current upcoming heating as is proposed in the analogous vertical climatic variation within tropical forest (Scheffers & Williams, ; Scheffers et al., ). Habitat‐driven thermal variation may exceed the expected rise of temperatures, and thermally buffered habitats can become climatic shelters for the organisms most exposed to the thermal shocks (see Lenoir & Svenning, ).…”

Section: Discussionmentioning

confidence: 99%

Elevational and microclimatic drivers of thermal tolerance in Andean Pristimantis frogs

Pintanel

Tejedo

Ron

et al. 2019

Journal of Biogeography

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Aim We analysed elevational and microclimatic drivers of thermal tolerance diversity in a tropical mountain frog clade to test three macrophysiological predictions: less spatial variation in upper than lower thermal limits (Bretts’ heat‐invariant hypothesis); narrower thermal tolerance ranges in habitats with less variation in temperature (Janzen's climatic variability hypothesis); and higher level of heat impacts at lower elevations. Location Forest and open habitats through a 4,230‐m elevational gradient across the tropical Andes of Ecuador. Method We examined variability in critical thermal limits (CTmax and CTmin) and thermal breadth (TB; CTmax–CTmin) in 21 species of Pristimantis frogs. Additionally, we monitored maximum and minimum temperatures at the local scale (tmax, tmin) and estimated vulnerability to acute thermal stress from heat (CTmax–tmax) and cold (tmin–CTmin), by partitioning thermal diversity into elevational and microclimatic variation. Results Our results were consistent with Brett's hypothesis: elevation promotes more variation in CTmin and tmin than in CTmax and tmax. Frogs inhabiting thermally variable open habitats have higher CTmax and tmax and greater TBs than species restricted to forest habitats, which show less climatic overlap across the elevational gradient (Janzen's hypothesis). Vulnerability to heat stress was higher in open than forest habitats and did not vary with elevation. Main conclusions We suggest a mechanistic explanation of thermal tolerance diversity in elevational gradients by including microclimatic thermal variation. We propose that the unfeasibility to buffer minimum temperatures locally may explain the rapid increase in cold tolerance (lower CTmin) with elevation. In contrast, the relative invariability in heat tolerance (CTmax) with elevation may revolve around the organisms’ habitat selection of open‐ and canopy‐buffered habitats. Secondly, on the basis of microclimatic estimates, lowland and upland species may be equally vulnerable to temperature increase, which is contrary to the pattern inferred from regional interpolated climate estimators.

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“…Second, verticality infers greater persistence to climatic instability (Davison and Chiba 2008, Scheffers et al 2013, Scheffers and Williams 2018. Vertical movements, either upwards in the canopy or downwards into the ground, afford more plastic ecologies and confer advantages over entirely ground-dwelling species due to a greater accessibility to micro-habitats and climates.…”

Section: Introductionmentioning

confidence: 99%

Vertical stratification influences global patterns of biodiversity

Oliveira

Scheffers

2018

Ecography

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Species distributions in terrestrial ecosystems are three‐dimensional, spanning both the horizontal landscape and the vertical space provided by the physical environment. Classical hypotheses suggest that communities become more vertically stratified with increasing species richness, owing to reduced competition or finer niche subdivision. However, this assertion remains untested in the context of the broader realm of biogeography. Here, integrating traits and distribution data for amphibians globally, we show how vertical strategies interact with the physical and climatic environments to govern global patterns of species richness and community composition. Our results reveal a marked latitudinal shift in strategies of vertical habitat use, from highly arboreal assemblages in the tropics to highly fossorial assemblages in sub‐tropical and temperate regions. Arboreality is strongly associated with precipitation, vegetation structure and climatic stability, whereas fossoriality is more common in dry environments with high diurnal temperature range and low vegetation structure. These analyses shed light on the importance of vertical stratification for species coexistence in species‐rich regions. As certain tropical habitats become drier from climate change, the rich biological diversity that is emblematic of the tropics may transition from vertically stratified to ‘flattened’, with future communities living mostly on or beneath the ground.

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Tropical mountain passes are out of reach – but not for arboreal species

Cited by 22 publications

References 68 publications

Extending Janzen’s hypothesis to temperate regions: A test using subterranean ecosystems

Extending Janzen’s hypothesis to temperate regions: A test using subterranean ecosystems

Elevational and microclimatic drivers of thermal tolerance in Andean Pristimantis frogs

Vertical stratification influences global patterns of biodiversity

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