Ecometrics: A trait-based approach to paleoclimate and paleoenvironmental reconstruction

Peer reviewe

Perspectives on Informal Learning: Cross-Disciplinary Concepts and A New Venue for Adult Education

Informal learning is a canonical concept in adult education but is used differently in other disciplines. We explore those differences and describe a new opportunity for adult education

Body Size Evolution in Insular Speckled Rattlesnakes (Viperidae: Crotalus mitchellii)

Background Speckled rattlesnakes (Crotalus mitchellii) inhabit multiple islands off the coast of Baja California, Mexico. Two of the 14 known insular populations have been recognized as subspecies based primarily on body size divergence from putative mainland ancestral populations; however, a survey of body size variation from other islands occupied by these snakes has not been previously reported. We examined body size variation between island and mainland speckled rattlesnakes, and the relationship between body size and various island physical variables among 12 island populations. We also examined relative head size among giant, dwarfed, and mainland speckled rattlesnakes to determine whether allometric differences conformed to predictions of gape size (and indirectly body size) 2evolving in response to shifts in prey size. Methodology/Principal Findings Insular speckled rattlesnakes show considerable variation in body size when compared to mainland source subspecies. In addition to previously known instances of gigantism on Ángel de la Guarda and dwarfism on El Muerto, various degrees of body size decrease have occurred frequently in this taxon, with dwarfed rattlesnakes occurring mostly on small, recently isolated, land-bridge islands. Regression models using the Akaike information criterion (AIC) showed that mean SVL of insular populations was most strongly correlated with island area, suggesting the influence of selection for different body size optima for islands of different size. Allometric differences in head size of giant and dwarf rattlesnakes revealed patterns consistent with shifts to larger and smaller prey, respectively. Conclusions/Significance Our data provide the first example of a clear relationship between body size and island area in a squamate reptile species; among vertebrates this pattern has been previously documented in few insular mammals. This finding suggests that selection for body size is influenced by changes in community dynamics that are related to graded differences in area over what are otherwise similar bioclimatic conditions. We hypothesize that in this system shifts to larger prey, episodic saturation and depression of primary prey density, and predator release may have led to insular gigantism, and that shifts to smaller prey and increased reproductive efficiency in the presence of intense intraspecific competition may have led to insular dwarfism

The past as a lens for biodiversity conservation on a dynamically changing planet

We are in the midst of a major biodiversity crisis, with deep impacts on the functioning of ecosystems and derived benefits to people (1, 2). But we still have time to pull back. To do so, it is imperative that we learn from plants’ and animals’ pastactions (3, 4). Conservation biology, ecology, and paleontology all emphasize that natural systems must exhibit resilience and dynamic responses to rapid environmental changes (3, 5, 6). Both climate and land-use change have accelerated over thepast decades, underscoring the urgency for increased understanding and action (7–9). The cumulative effects of these disruptions are not additive or systematic; rather, they posecomplex, dynamic environmental challenges to ecological systems (see “dynamic systems” Table 1). With the dramatic ecological effects from climate fluctuations and increasing in stability of the fabric of life (10–12), we anticipate that biota will dramatically shift their ranges, reconfiguring ecological communities across Earth’s natural landscapes (13) (Fig. 1).Today’s most prevalent conservation approaches focus on the maintenance of static reserves. These approaches need to be supplemented by approaches that facilitate dynamic ecological shifts using flexible strategies that involve local stake holders(14–17). In addition, given the magnitude, rates, and complex interactions of anthropogenic and climatic change occurring today, these conservation approaches must beinformed by research that spans time scales to infer likely responses (18). This special feature integrates research from across spatial and temporal scales to explore how ecosystem sand communities function dynamically to respond to large scale environmental change, highlighting proposed solutions for conserving biodiversity on a rapidly changing planetFil: MacGuire, Jenny L.. Georgia Institute of Techology; Estados UnidosFil: Michelle Lawing, A.. Georgia Institute of Techology; Estados UnidosFil: Díaz, Sandra Myrna. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Stenseth, Nils Chr. University of Oslo; Noruega. International Union of Biological Sciences; Franci

Continuously Growing Rodent Molars Result from a Predictable Quantitative Evolutionary Change over 50 Million Years

The fossil record is widely informative about evolution, but fossils are not systematically used to study the evolution of stem-cell-driven renewal. Here, we examined evolution of the continuous growth (hypselodonty) of rodent molar teeth, which is fuelled by the presence of dental stem cells. We studied occurrences of 3,500 North American rodent fossils, ranging from 50 million years ago (mya) to 2 mya. We examined changes in molar height to determine whether evolution of hypselodonty shows distinct patterns in the fossil record, and we found that hypselodont taxa emerged through intermediate forms of increasing crown height. Next, we designed a Markov simulation model, which replicated molar height increases throughout the Cenozoic and, moreover, evolution of hypselodonty. Thus, by extension, the retention of the adult stem cell niche appears to be a predictable quantitative rather than a stochastic qualitative process. Our analyses predict that hypselodonty will eventually become the dominant phenotype.Peer reviewe

Limitations of Climatic Data for Inferring Species Boundaries: Insights from Speckled Rattlesnakes

Phenotypes, DNA, and measures of ecological differences are widely used in species delimitation. Although rarely defined in such studies, ecological divergence is almost always approximated using multivariate climatic data associated with sets of specimens (i.e., the "climatic niche"); the justification for this approach is that species-specific climatic envelopes act as surrogates for physiological tolerances. Using identical statistical procedures, we evaluated the usefulness and validity of the climate-as-proxy assumption by comparing performance of genetic (nDNA SNPs and mitochondrial DNA), phenotypic, and climatic data for objective species delimitation in the speckled rattlesnake (Crotalus mitchellii) complex. Ordination and clustering patterns were largely congruent among intrinsic (heritable) traits (nDNA, mtDNA, phenotype), and discordance is explained by biological processes (e.g., ontogeny, hybridization). In contrast, climatic data did not produce biologically meaningful clusters that were congruent with any intrinsic dataset, but rather corresponded to regional differences in atmospheric circulation and climate, indicating an absence of inherent taxonomic signal in these data. Surrogating climate for physiological tolerances adds artificial weight to evidence of species boundaries, as these data are irrelevant for that purpose. Based on the evidence from congruent clustering of intrinsic datasets, we recommend that three subspecies of C. mitchellii be recognized as species: C. angelensis, C. mitchellii, and C. Pyrrhus

Merging paleobiology with conservation biology to guide the future of terrestrial ecosystems

Conservation of species and ecosystems is increasingly difficult because anthropogenic impacts are pervasive and accelerating. Under this rapid global change, maximizing conservation success requires a paradigm shift from maintaining ecosystems in idealized past states toward facilitating their adaptive and functional capacities, even as species ebb and flow individually. Developing effective strategies under this new paradigm will require deeper understanding of the long-term dynamics that govern ecosystem persistence and reconciliation of conflicts among approaches to conserving historical versus novel ecosystems. Integrating emerging information from conservation biology, paleobiology, and the Earth sciences is an important step forward on the path to success. Maintaining nature in all its aspects will also entail immediately addressing the overarching threats of growing human population, overconsumption, pollution, and climate change.Peer reviewe

Pleistocene Climate, Phylogeny, and Climate Envelope Models: An Integrative Approach to Better Understand Species' Response to Climate Change

Mean annual temperature reported by the Intergovernmental Panel on Climate Change increases at least 1.1°C to 6.4°C over the next 90 years. In context, a change in climate of 6°C is approximately the difference between the mean annual temperature of the Last Glacial Maximum (LGM) and our current warm interglacial. Species have been responding to changing climate throughout Earth's history and their previous biological responses can inform our expectations for future climate change. Here we synthesize geological evidence in the form of stable oxygen isotopes, general circulation paleoclimate models, species' evolutionary relatedness, and species' geographic distributions. We use the stable oxygen isotope record to develop a series of temporally high-resolution paleoclimate reconstructions spanning the Middle Pleistocene to Recent, which we use to map ancestral climatic envelope reconstructions for North American rattlesnakes. A simple linear interpolation between current climate and a general circulation paleoclimate model of the LGM using stable oxygen isotope ratios provides good estimates of paleoclimate at other time periods. We use geologically informed rates of change derived from these reconstructions to predict magnitudes and rates of change in species' suitable habitat over the next century. Our approach to modeling the past suitable habitat of species is general and can be adopted by others. We use multiple lines of evidence of past climate (isotopes and climate models), phylogenetic topology (to correct the models for long-term changes in the suitable habitat of a species), and the fossil record, however sparse, to cross check the models. Our models indicate the annual rate of displacement in a clade of rattlesnakes over the next century will be 2 to 3 orders of magnitude greater (430-2,420 m/yr) than it has been on average for the past 320 ky (2.3 m/yr)

The geographic and morphologic response of species and communities to their climate and environment

How species will cope with the effects of anthropogenic change is now a subject of great concern. The response of species to climate change can be measured geographically with species distribution models or morphologically with community-averaged traits. In this dissertation, I integrate rich geological and paleoclimatic data with an evolutionary concept of climatic niches to quantify the responses of species to climate change. I show that biotic interactions, namely competitive exclusion, along with climate tolerances, can shape species borders, exemplified by sister species within the rattlesnake genus Crotalus. Projecting phylogenetically informed species distribution models over the last three glacial-interglacial cycles indicates that species within Crotalus were not able to adapt as fast as climate changed. The rate of geographic displacement of suitable habitat over the next century will be two to three orders of magnitude faster than it was over the last 320 ky. A deep time perspective of spiny lizard (Sceloporus ) response to climate change, early Miocene to present, shows that origins, diversification, and subsequent species richness are not coincident in geographic space. Instead, the first lineages to diverge tracked their habitat by moving south as the climate cooled after the Miocene climatic optimum and evolved adaptations such as viviparity to cope with the new climates. Species response to climate change can also be measured through the interaction between environments and morphological traits. I describe a community level trait-environment association in North American snakes and demonstrate that historic changes in community-averaged traits track the changes in macrovegetation. This dissertation demonstrates that geographically explicit models integrating data and methods from geology, ecology, evolution, and climate science provide a deeper understanding to the biology of climate change. These models explicitly address how species responded to climate change in the past to inform expectations of how they will respond in the future