THE EVOLUTION OF ENVIRONMENTAL TOLERANCE AND RANGE SIZE: A COMPARISON OF GEOGRAPHICALLY RESTRICTED AND WIDESPREADMIMULUS

Abstract

The geographic ranges of closely related species can vary dramatically, yet we do not fully grasp the mechanisms underlying such variation. The niche breadth hypothesis posits that species that have evolved broad environmental tolerances can achieve larger geographic ranges than species with narrow environmental tolerances. In turn, plasticity and genetic variation in ecologically important traits and adaptation to environmentally variable areas can facilitate the evolution of broad environmental tolerance.We used five pairs of western North American monkeyflowers to experimentally test these ideas by quantifying performance across eight temperature regimes. In four species pairs, species with broader thermal tolerances had larger geographic ranges, supporting the niche breadth hypothesis. As predicted, species with broader thermal tolerances also had more within-population genetic variation in thermal reaction norms and experienced greater thermal variation across their geographic ranges than species with narrow thermal tolerances. Species with narrow thermal tolerance may be particularly vulnerable to changing climatic conditions due to lack of plasticity and insufficient genetic variation to respond to novel selection pressures. Conversely, species experiencing high variation in temperature across their ranges may be buffered against extinction due to climatic changes because they have evolved tolerance to a broad range of temperatures. K E Y W O R D S :Climatic variability hypothesis, geographic range size, genetic variation, niche breadth, specialist-generalist tradeoffs, thermal performance curve.

Assessing Mammal Exposure to Climate Change in the Brazilian Amazon

“…Besides living in areas where greater climate change is expected, Primates in the Amazon are climatic and geographically restricted and thereby expected to be more sensitive to climate change [7,17,49]. In addition, these species will probably be unable to keep pace with climate change even at relatively low magnitude of climate change due to high velocity of climate change expected in the tropics and poor dispersal abilities [50,51].…”

Ecological genetics of range size variation in Boechera spp. (Brassicaceae)

“…2013) and should therefore display elevated phenotypic variation and plasticity (Sheth and Angert 2014) relative to rare species. The increased phenotypic variation found in widespread species was due to both strong spatial structure (>3× increase in among‐population variance relative to rare species) and increased phenotypic plasticity.…”

“…A high degree of plasticity will expand the amount of suitable habitat (Baker and Stebbins 1965; Pohlman et al. 2005; Sheth and Angert 2014), and studies have shown that increased plasticity can be beneficial when invading new sites (Loomis and Fishman 2009), surviving stress (Heschel et al. 2004), or persisting through changing environmental conditions (Chevin and Lande 2011).…”

“…2009). Indeed, Sheth and Angert (2014) recently demonstrated that widespread Mimulus species display a greater range of thermal tolerances than rare congeners. Finally, a trade‐off between plasticity and local‐scale specialization (jack of all trades, master of none) may drive patterns of niche breadth and the extent of the geographic range (Futuyma and Moreno 1988; Whitlock 1996; Caley and Munday 2003).…”

Morphological and genetic characterization among wild populations of copao (Eulychnia acida Phil.), cactus endemic to Chile

“…Ability to adapt when the environment changes, is the result of their genetic diversity, condition that needs to be studied. Insufficient diversity would lead species to restrict their geographic distribution and be more vulnerable to extinction under novel selection pressure (Sheth and Angert, 2014). Small populations with low diversity might also experience higher levels of inbreeding (Oleas et al, 2014).…”