Ecological Gradients in Diversity and Abundance: A Search for Patterns and Processes in Small Mammal Communities

The University of Kansas has long historical connections with Central America and the many Central Americans who have earned graduate degrees at KU. This work is part of the Central American Theses and Dissertations collection in KU ScholarWorks and is being made freely available with permission of the author through the efforts of Professor Emeritus Charles Stansifer of the History department and the staff of the Scholarly Communications program at the University of Kansas Libraries’ Center for Digital Scholarship.One of the most fundamental questions in ecology is: what are the patterns of diversity and the mechanisms that produce them? Many biological theories have been proposed to explain latitudinal and elevational diversity gradients, but no accepted, general explanation for the distribution of biodiversity has surfaced. Two necessities for establishing a general diversity theory are utilizing more rigorous statistical methods to test hypotheses, and including more comparative analyses. With these aims in mind, I examine the predictability of null models and biological diversity hypotheses for latitudinal and elevational gradients in diversity and abundance of small mammals. The unimodal distribution of diversity in North American desert rodents was highly consistent with the mid-domain effect—a spatial constraint null model incorporating the overlap of variably sized ranges within a bounded region. Deviations from the null model demonstrated a localized pulse in richness caused by a local hard boundary, the Baja peninsula. The small mammal diversity along an elevational transect in Costa Rica was unimodal with species richness highest between 1000-1300 m. The spatial constraints of montane topography appear to influence the diversity pattern, although climatic conditions including an intermediate rainfall and temperature regime, and distance from the persistent cloud cap also are correlated with the pattern. The global analysis of elevational diversity trends for non-volant small mammals revealed a ubiquitous pattern of mid-elevational peaks in species richness. The mid-domain null model was not generally predictive across all datasets. Diversity peaks occurred at higher elevations on taller mountains (Massenerhebung effect), which is consistent with climatic factors working in concert to produce elevationally correlated habitat bands. Gamma diversity patterns demonstrated higher altitudinal peaks in species diversity as latitude increased. An examination of replicates in alpha diversity studies along elevational transects found high variability both temporally and spatially, emphasizing the necessity of replication in well-designed studies of diversity gradients. In an examination of range size-abundance trends no strong relationship was found between abundance or body size with elevational range size. Local and regional abundances across elevational ranges generally revealed a trend toward higher abundances at mid-range, although usually not centered at the range midpoint

A Systematic Review of Global Drivers of Ant Elevational Diversity

Ant diversity shows a variety of patterns across elevational gradients, though the patterns and drivers have not been evaluated comprehensively. In this systematic review and reanalysis, we use published data on ant elevational diversity to detail the observed patterns and to test the predictions and interactions of four major diversity hypotheses: thermal energy, the mid-domain effect, area, and the elevational climate model. Of sixty-seven published datasets from the literature, only those with standardized, comprehensive sampling were used. Datasets included both local and regional ant diversity and spanned 80° in latitude across six biogeographical provinces. We used a combination of simulations, linear regressions, and non-parametric statistics to test multiple quantitative predictions of each hypothesis. We used an environmentally and geometrically constrained model as well as multiple regression to test their interactions. Ant diversity showed three distinct patterns across elevations: most common were hump-shaped mid-elevation peaks in diversity, followed by low-elevation plateaus and monotonic decreases in the number of ant species. The elevational climate model, which proposes that temperature and precipitation jointly drive diversity, and area were partially supported as independent drivers. Thermal energy and the mid-domain effect were not supported as primary drivers of ant diversity globally. The interaction models supported the influence of multiple drivers, though not a consistent set. In contrast to many vertebrate taxa, global ant elevational diversity patterns appear more complex, with the best environmental model contingent on precipitation levels. Differences in ecology and natural history among taxa may be crucial to the processes influencing broad-scale diversity patterns

Just bird food? – On the value of invertebrate macroecology

Recent reviews have highlighted the dominance of vertebrates and plants in macroecological and biogeographical publications while invertebrates are underrepresented despite their global ecological relevance and vast diversity. We argue that although the study of invertebrate biogeography and macroecology has data limitations and thus lags behind in global research coverage, it has left a strong mark on the development of the discipline and has continuing potential to significantly shape its future. First, we detail how historical collecting and identification impediments caused decelerated progress at the macro-scale. Second, we show the quantitative impact of early invertebrate studies in contrast to lowered current representation. Third, we discuss ways in which authors, editors, and reviewers may foster invertebrate studies in macroecology. These include an honest appreciation of the value of study replication, of understudied but diverse taxa, and of the ecological traits that make invertebrates unique in comparison to vertebrates (e.g., wider array of life cycles, symbioses, and ecological niches), as well as the expanded potential for experimentation and manipulation

Redescription of the enigmatic long-tailed rat Sigmodontomys aphrastus (Cricetidae: Sigmodontinae) with comments on taxonomy and natural history

Sigmodontomys aphrastus, the long-tailed rat, is an exceedingly rare rodent species from montane regions of Central and South America of which very little is known ecologically or systematically. It has been variously placed in the genera Oryzomys, Nectomys, and Sigmodontomys based on the five previously known specimens. Recent phylogenetic analyses (Weksler 2006) have shown that S. aphrastus occurs in a monophyletic clade composed of S. alfari and Melanomys caliginosus with M. caliginosus as the proposed sister taxon. Two new individuals were collected in northwestern Costa Rica’s Cordillera de Tilarán. These new specimens and the other five known specimens are used to redescribe the species, detail measurements of external and cranial morphology, and compare S. aphrastus to similar appearing, sympatric species (Nephelomys albigularis and N. devius) and proposed closely related species (Sigmodontomys alfari, Mindomys hammondi, and Melanomys caliginosus). New ecological data is presented and the general knowledge of its natural history is summarized. The phylogenetic relatedness of S. aphrastus with purported sister taxa remains unresolved until combined molecular and morphological analyses are conducted.Resumen—Sigmodontomys aphrastus, la rata de cola larga, es una especie rara de rodedor de las montañas de America Central y Sur de la cual se conoce muy poco acerca de su ecología y sistemática. Esta especie ha sido clasificada en el género Oryzomys, Nectomys, y Sigmodontomys basado en solo cinco especímenes. Análisis filogenéticos recientes (Weksler 2006) han demonstrado que S. aphrastus se encuentra en un clado monofilético compuesto de S. alfari y Melanomys caliginosus con M. caliginosus propuesto como la especie hermana. Dos nuevos individuos fueron recolectados en el noreste de Costa Rica en la Cordillera de Tilarán. Estos dos nuevos especímenes y junto con los cinco anteriores son usados a describir nuevamente la especie, detallar sus medidas morfométricas externas y craneales, y comparar S. aphrastus con especies simpátricas similares (Nephelomys albigularis and N. devius) y especies que han sido propuestas como dentro del mismo clado (Sigmodontomys alfari, Mindomys hammondi, y Melanomys caliginosus). Presentamos nuevos datos ecológicos y resumimos el conocimiento de su historia natural. La relación filogenética de S. aphrastus con las especies propuestas como del mismo clado no sera resuelto hasta que analisis moleculares y morfologicos sean llevados a cabo

Microbes do not follow the elevational diversity patterns of plants and animals

The elevational gradient in plant and animal diversity is one of the most widely documented patterns in ecology and, although no consensus explanation exists, many hypotheses have been proposed over the past century to explain these patterns. Historically, research on elevational diversity gradients has focused almost exclusively on plant and animal taxa. As a result, we do not know whether microbes exhibit elevational gradients in diversity that parallel those observed for macroscopic taxa. This represents a key knowledge gap in ecology, especially given the ubiquity, abundance, and functional importance of microbes. Here we show that, across a montane elevational gradient in eastern Peru, bacteria living in three distinct habitats (organic soil, mineral soil, and leaf surfaces) exhibit no significant elevational gradient in diversity (r2 0.1 in all cases), in direct contrast to the significant diversity changes observed for plant and animal taxa across the same montane gradient (r2 > 0.75, P < 0.001 in all cases). This finding suggests that the biogeographical patterns exhibited by bacteria are fundamentally different from those of plants and animals, highlighting the need for the development of more inclusive concepts and theories in biogeography to explain these disparities

Guidelines of the American Society of Mammalogists for the use of wild mammals in research

Guidelines for use of wild mammal species are updated from the American Society of Mammalogists (ASM) 2007 publication. These revised guidelines cover current professional techniques and regulations involving mammals used in research and teaching. They incorporate additional resources, summaries of procedures, and reporting requirements not contained in earlier publications. Included are details on marking, housing, trapping, and collecting mammals. It is recommended that institutional animal care and use committees (IACUCs), regulatory agencies, and investigators use these guidelines as a resource for protocols involving wild mammals. These guidelines were prepared and approved by the ASM, working with experienced professional veterinarians and IACUCs, whose collective expertise provides a broad and comprehensive understanding of the biology of nondomesticated mammals in their natural environments. The most current version of these guidelines and any subsequent modifications are available at the ASM Animal Care and Use Committee page of the ASM Web site (http://mammalsociety.org/committees/index.asp).American Society of Mammalogist

Another rejection of the more-individuals-hypothesis: Carrion beetles (Silphidae, Coleoptera) in the Southern Rocky Mountains

Beetles are the most diverse animal clade on the planet, and understanding the mechanisms underlying their diversity patterns is critical to understanding animal biodiversity in general. Using carrion beetles (Silphidae; Coleoptera), I test the more-individuals hypothesis (MIH), consisting of positive climatic impacts on food resources leading to increased abundance and then diversity. I also test competing mechanistic hypotheses, including interacting effects of climate, local vegetation, habitat diversity, habitat heterogeneity, soil diversity, and elevational area. Carrion beetle species richness and abundances were estimated using 40 standardized pitfall traps set for 90 days at 30 survey sites on two elevational gradients in the Front Range and San Juan Mountains, Colorado, USA. Standardized measurements assessed 13 vegetative characteristics, food resources (mammal abundances), soil diversity, habitat diversity, elevational area, temperature, precipitation and net primary productivity at each site. Structural equation models were used to test competing diversity hypotheses and mechanisms. Species richness peaked at intermediate elevations on both gradients, whereas abundance was unimodal on one gradient and decreasing on the other. The MIH mechanism was rejected; all four potential SEM model constructions were unsupported and the majority of all SEM models did not support relationships between abundance and diversity or climate and food resources. The best SEM model included direct influences of temperature, vegetation biomass, and food resources but with separate effects on diversity and abundance. Carrion beetles were more diverse and abundant in sites with dense understory vegetation and warm temperatures, while higher abundances were also linked to more food resources. This climate-biotic relationship is likely due to a need for microclimates and microhabitats to mediate physiological tradeoffs of desiccation and thermoregulation with predation. This suggests a general hypothesis for beetle diversity and abundance, particularly on arid-based mountains globally

Another rejection of the more-individuals-hypothesis: Carrion beetles (Silphidae, Coleoptera) in the Southern Rocky Mountains

Beetles are the most diverse animal clade on the planet, and understanding the mechanisms underlying their diversity patterns is critical to understanding animal biodiversity in general. Using carrion beetles (Silphidae; Coleoptera), I test the more-individuals hypothesis (MIH), consisting of positive climatic impacts on food resources leading to increased abundance and then diversity. I also test competing mechanistic hypotheses, including interacting effects of climate, local vegetation, habitat diversity, habitat heterogeneity, soil diversity, and elevational area. Carrion beetle species richness and abundances were estimated using 40 standardized pitfall traps set for 90 days at 30 survey sites on two elevational gradients in the Front Range and San Juan Mountains, Colorado, USA. Standardized measurements assessed 13 vegetative characteristics, food resources (mammal abundances), soil diversity, habitat diversity, elevational area, temperature, precipitation and net primary productivity at each site. Structural equation models were used to test competing diversity hypotheses and mechanisms. Species richness peaked at intermediate elevations on both gradients, whereas abundance was unimodal on one gradient and decreasing on the other. The MIH mechanism was rejected; all four potential SEM model constructions were unsupported and the majority of all SEM models did not support relationships between abundance and diversity or climate and food resources. The best SEM model included direct influences of temperature, vegetation biomass, and food resources but with separate effects on diversity and abundance. Carrion beetles were more diverse and abundant in sites with dense understory vegetation and warm temperatures, while higher abundances were also linked to more food resources. This climate-biotic relationship is likely due to a need for microclimates and microhabitats to mediate physiological tradeoffs of desiccation and thermoregulation with predation. This suggests a general hypothesis for beetle diversity and abundance, particularly on arid-based mountains globally

Appendix A. A table listing all elevational data sets of small mammal diversity, including data specifics, null model and analysis values, and a list of data sources used in the review.

A table listing all elevational data sets of small mammal diversity, including data specifics, null model and analysis values, and a list of data sources used in the review