Caviomorphs

Despite being the most studied species on the planet, ecologists typically do not study humans the same way we study other organisms. My Ph.D. thesis contributes to scientific development in two ways: i) synthesizing our understand of the inter and intraspecific variation in social behavior in an understudied rodent lineage, the caviomorphs, providing a comparative context to understand social evolution in general, and ii) developing a macroecological approach to understand the metabolic trajectory of the human species. Through comparative analysis, chapter 2 synthesizes the available information on the diversity of sociality in the caviomorph rodents, both within and across species. Studies and theory derived from better-studied mammalian taxa establish an integrative and comparative framework from which to examine social systems in caviomorphs. We synthesize the literature to evaluate variation in space use, group size, mating systems, and parental care strategies in caviomorphs in the context of current hypotheses. We highlight unique aspects of caviomorph biology and offer potentially fruitful lines for future research both at the inter and intraspecific levels. We can gain unique insights into the ecological drivers and evolutionary significance of diverse animal societies by studying this diverse taxon. Chapter 3 outlines core ecological principles that should be integral to a science of sustainability: 1) physical conservation laws govern the flows of energy and materials between human systems and the environment, 2) smaller systems are connected by these flows to larger systems in which they are embedded, 3) global constraints ultimately limit flows at smaller scales. Over the past few decades, decreasing per-capita rates of consumption of petroleum, phosphate, agricultural land, fresh water, fish, and wood indicate that the growing human population has surpassed the capacity of the Earth to supply enough of these essential resources to sustain even the current population and level of socioeconomic development. Chapter 4 applies a socio-metabolic perspective of the urban transition coupled with empirical examination of cross-country data spanning decades. It highlights the central role of extra-metabolic energy in global urbanization and the coinciding transition from resource extraction to industrial and service economies. The global urban transition from resource producers in rural areas, to industrial and service employment in urban systems is fuelled by supplementing extra- metabolic energy in the form of fossil fuels for decreasing human and animal labor. Collectively, I hope this work demonstrates the utility of comparative analysis and synthesis in understanding the evolutionary ecology of sociality and the power of a macroecological approach in understanding the metabolic ecology and trajectory of the human species.

Understanding the spatial distribution of species sheds light on the group's biogeographical history, offers clues to the drivers of diversity, and helps to guide conservation strategies. Here, we compile geographic range information for South America's diverse rodents, whose 14 families comprise ~50% of the continent's mammalian species. The South Ameri-can rodent fauna is dominated by independent and temporally staggered radiations of caviomorph and sigmodontine groups. We mapped species richness and turnover of all rodents and the principal clades to identify the main predictors of diversity patterns. Species richness was highest in the Andes, with a secondary hotspot in Atlantic Forest and some regions of considerable richness in Amazonia. Differences in richness were evident between the caviomorphs and sigmodontines, the former showing the greatest richness in tropical forests whereas the latter show—and largely determine—the all-rodent pattern. Elevation was the main predictor of sigmodontine richness, whereas temperature was the principal variable correlated with richness of caviomorphs. Across clades, species turnover was highest along the Andes and was best explained by elevational relief. In South America, the effects of the familiar latitudinal gradient in species richness are mixed with a strong longitudinal effect, triggered by the importance of elevation and the position of the Andes. Both lati-tudinal and elevational effects help explain the complicated distribution of rodent diversity across the continent. The continent's restricted-range species—those seemingly most vulnerable to localized disturbance—are mostly distributed along the Andes and in Atlantic Forest, with the greatest concentration in Ecuador. Both the Andes and Atlantic Forest are known hotspots for other faunal and floral components. Contrasting patterns of the older caviomorph and younger sigmodontine radiations underscore the interplay of both historical and ecological factors in determining present-day diversity patterns.

ABSTRACT Burrow construction in the subterranean Ctenomys talarum (Rodentia: Ctenomyidae) primarily occurs by scratch-digging. In this study, we compared the limbs of an ontogenetic series of C. talarum to identify variation in bony elements related to fossorial habits using a morphometrical and biomechanical approach.Diameters and functional lengths of long bones were
measured and 10 functional indices were constructed. We
found that limb proportions of C. talarum undergo significant changes throughout postnatal ontogeny, and no significant differences between sexes were observed. Five of six forelimb indices and two of four hindlimb indices showed differences between ages. According to discriminant analysis, the indices that contributed most to discrimination among age groups were robustness of the humerus and ulna, relative epicondylar width, crural and brachial indices, and index of fossorial ability (IFA).
Particularly, pups could be differentiated from juveniles and adults by more robust humeri and ulnae, wider epicondyles, longer middle limb elements, and a proportionally shorter olecranon. Greater robustness indicated a possible compensation for lower bone stiffness while wider epicondyles may be associated to improved effective forces in those muscles that originate onto them, compensating the lower muscular development. The gradual increase in the IFA suggested a gradual enhancement in the scratch-digging performance due to an improvement in the mechanical advantage of forearm extensors. Middle limb indices were higher in pups than in juveniles–adults, reflecting relatively more gracile limbs in their middle segments, which is in accordance with their incipient fossorial ability. In sum, our results show that in C. talarum some scratch-digging adaptations are already present during early postnatal ontogeny, which suggests that they are prenatally shaped, and other traits develop progressively. The role of early digging behavior as a factor influencing on morphology development is discussed.