Ecological release in the sand

Submitted by editor on 24 April 2015.Get the paper!

When a population encounters a newly-formed habitat, colonizers of the new habitat often undergo “ecological release,” meaning that they expand their ecological niche in the new habitat compared to their original habitat.  Ecological release usually occurs because in a newly-colonized habitat, individuals have fewer competitors and predators than they had in their original habitat, and are therefore able to exploit a wider variety of resources in the newly-colonized habitat.  The White Sands dune formation in New Mexico, U.S.A. is a dune field made of white gypsum, which contrasts sharply with the surrounding dark soil habitat in the Tularosa Basin.  The White Sands dune field was formed about 7000 years ago, and has subsequently has been colonized by three species of lizards.  All three lizard species show blanched coloration in populations living on the White Sands formation compared to their darker counterparts living in the surrounding dark soil habitat, making the White Sands lizard community a textbook example of convergent evolution (Rosenblum 2005, 2006; Rosenblum et al. 2010; Rosenblum and Harmon 2011). 

Previous research has demonstrated that lizards living on the White Sands formation have undergone ecological release compared to lizards from the surrounding dark soil habitat, due in large part to the lower density of predators and competitor lizard species that occur in White Sands (Des Roches et al. 2011, 2014, 2015).  In our recent paper, “Evidence for ecological release over a fine spatial scale in a lizard from the White Sands formation,” we wanted to determine whether ecological release was evident over an even finer spatial scale by comparing resource use of one lizard species, the Southwestern Fence Lizard, in the center of the White Sands dune formation and the narrow ecotone, or habitat edge, between White Sands and the surrounding dark soil habitats.  We predicted that lizards from the central dunes would exhibit broadened resource use compared to lizards from the ecotone.  We first conducted bird surveys in both the central dunes and ecotone habitats to measure abundance of birds that could act as lizard predators.  Next, we measured microhabitat-scale resource use by comparing perch selection of lizards in both habitats.  Finally, we attached miniature transmitters to male lizards and used radio-telemetry to measure landscape-scale resource use by quantifying home range sizes and daily distances traveled by lizards in both habitats.  We found that central dunes lizards used a greater diversity of perch types, and had greater variation in both home range size and daily distances traveled, than ecotone lizards.  There were fewer predatory bird species in the central dunes than on the ecotone, and there was a tendency for fewer predation events in the central dunes than on the ecotone.  Our results demonstrate that ecological release is detectable over a fine habitat gradient, such as between the center of a recently-colonized habitat and its ecotone with the surrounding ecosystem.  Moreover, the lizards in our study, with body masses of 6.0 – 8.2 g, are the smallest lizard species ever to be monitored using radio-telemetry.

The authors through Jeanine M. Refsnider

Literature cited

Des Roches, S. et al. 2011. Ecological release in White Sands lizards. - Ecol Evol 1: 571-578.

Des Roches, S. et al. 2014. Beyond black and white: divergent behaviour and performance in three rapidly evolving lizard species at White Sands. - Biol J Linnean Soc 111: 169-182.

Des Roches, S. et al. 2015. Ecological release and directional change in White Sands lizard trophic ecomorphology. - Evol Ecol 29: 1-16.

Rosenblum, E. B. 2005. The role of phenotypic plasticity in color variation of Tularosa Basin lizards. - Copeia 2005(3): 586-596.

Rosenblum, E. B. 2006. Convergent evolution and divergent selection: lizards at the White Sands ecotone. - Am Nat 167: 1-15.

Rosenblum, E. B. and Harmon, L. J. 2011. “Same same but different”: replicated ecological speciation at White Sands. - Evolution 65: 946-960.

Rosenblum, E. B. et al. 2010. Molecular and functional basis of phenotypic convergence in white lizards at White Sands. - Proc Natl Acad Sci 107: 2113-2117.

 

 

 

White Sands National Monument (New Mexico, U.S.A.) is a recently-formed habitat made of white gypsum sand dunes.  We studied lizards on the ecotone and in the center of the dune formation to determine whether lizards used resources differently in the two habitat types (photos by J. Refsnider).  The dark soil habitat surrounding the White Sands formation is visible on the right side of the aerial photograph.

 

 

 

A male southwestern fence lizard (Sceloporus cowlesi) at White Sands National Monument, New Mexico U.S.A., engages in a push-up display to attract potential mates and demonstrate territoriality to male rivals.  This lizard is carrying a miniature radio-transmitter so researchers can monitor him daily and record habitat use, movement patterns, and home range size.  (Photo by H. Streby)

 

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