Katherine M. Thibault

Impact of an extreme climatic event on community assembly

Extreme climatic events are predicted to increase in frequency and magnitude, but their ecological impacts are poorly understood. Such events are large, infrequent, stochastic perturbations that can change the outcome of entrained ecological processes. Here we show how an extreme flood event affected a desert rodent community that has been monitored for 30 years. The flood (i) caused catastrophic, species-specific mortality; (ii) eliminated the incumbency advantage of previously dominant species; (iii) reset long-term population and community trends; (iv) interacted with competitive and metapopulation dynamics; and (v) resulted in rapid, wholesale reorganization of the community. This and a previous extreme rainfall event were punctuational perturbations—they caused large, rapid population- and community-level changes that were superimposed on a background of more gradual trends driven by climate and vegetation change. Captured by chance through long-term monitoring, the impacts of such large, infrequent events provide unique insights into the processes that structure ecological communities.

Zero-sum, the niche,and metacommunities: long-term dynamics of community assembly

Recent models of community assembly, structure, and dynamics have incorporated, to varying degrees, three mechanistic processes: resource limitation and interspecific competition, niche requirements of species, and exchanges between a local community and a regional species pool. Synthesizing 30 years of data from an intensively studied desert rodent community, we show that all of these processes, separately and in combination, have influenced the structural organization of this community and affected its dynamical response to both natural environmental changes and experimental perturbations. In addition, our analyses suggest that zero‐sum constraints, niche differences, and metacommunity processes are inextricably linked in the ways that they affect the structure and dynamics of this system. Explicit consideration of the interaction of these processes should yield a deeper understanding of the assembly and dynamics of other ecological communities. This synthesis highlights the role that long‐term data, especially when coupled with experimental manipulations, can play in assessing the fundamental processes that govern the structure and function of ecological communities.

TEMPORAL DYNAMICS IN THE STRUCTURE AND COMPOSITION OF A DESERT RODENT COMMUNITY

The rank-abundance distribution (RAD) represents the manner in which spe- cies divide resources. Community-specific division rules that determine resource allocation among species, and thereby the shape of the RAD, have been hypothesized to account for observed stability of local species richness over time. While the shape of the RAD has been well studied, the temporal dynamics of this distribution have received much less attention. Here we assess changes in the shape of the RAD through time in a desert rodent community in Arizona (USA). Because energy use may be more appropriate for studying resource division than abundance, we also evaluate an energetic equivalent of the RAD. Significant, directional trends in the shapes of both distributions are present in this com- munity. These changes are driven by trends in the relative abundances (or energy use) of Ranks 2, 3, and 4, and are significantly correlated with variation in total energy use by the community and with compositional change. Our results suggest that (1) rank-abundance and rank-energy distributions are not static and can change directionally through time, (2) species richness and rank distributions are not necessarily as intimately connected as early studies assumed, and (3) rank-abundance and rank-energy distributions are influenced by both the amount of energy available to the community and species-specific interactions.

Characterizing species abundance distributions across taxa and ecosystems using a simple maximum entropy model.

The species abundance distribution (SAD) is one of themost studied patterns in ecology due to its potential insights into commonness and rarity, community assembly, and patterns of biodiversity. It is well established that communities are composed of a few common and many rare species, and numerous theoretical models have been proposed to explain this pattern. However, no attempt has been made to determine how well these theoretical characterizations capture observed taxonomic and global-scale spatial variation in the general form of the distribution. Here, using data of a scope unprecedented in community ecology, we show that a simple maximum entropy model produces a truncated log-series distribution that can predict between 83% and 93% of the observed variation in the rank abundance of species across 15 848 globally distributed communities including birds, mammals, plants, and butterflies. This model requires knowledge of only the species richness and total abundance of the community to predict the full abundance distribution, which suggests that these factors are sufficient to understand the distribution for most purposes. Since geographic patterns in richness and abundance can often be successfully modeled, this approach should allow the distribution of commonness and rarity to be characterized, even in locations where empirical data are unavailable.

Trade‐offs in Community Properties through Time in a Desert Rodent Community

Resource limitation represents an important constraint on ecological communities, which restricts the total abundance, biomass, and community energy flux a given community can support. However, the exact relationship among these three measures of biological activity remains unclear. Here we use a simple framework that links abundance and biomass with an energetic constraint. Under constant energetic availability, it is expected that changes in abundance and biomass can result from shifts in the distribution of individual masses. We test these predictions using long‐term data from a desert rodent community. Total energy use for the community has not changed directionally for 25 years, but species composition has. As a result, the average body size has decreased by almost 50%, and average abundance has doubled. These results lend support to the idea of resource limitation on desert rodent communities and demonstrate that systems are able to maintain community energy flux in the face of environmental change, through changes in composition and structure.

Long-term insights into the influence of precipitation on community dynamics in desert rodents

Abstract Arid systems are characterized by spatiotemporal variability in resources and, as such, make ideal systems for examining the role of resource limitation in the long-term dynamics of populations. Using 28 years of data, we examine the long-term relationships of 3 guilds of desert rodent consumers with precipitation and primary productivity in a changing environment. Lags in rodent response to precipitation increased with increasing trophic level over the entire time series, consistent with resource limitation. However, we found that consumer–resource dynamics are complex and variable through time. Precipitation exhibited increasing influence on both primary producers and consumers in this system over time. Experimental evidence suggests that reorganization of community composition, coincident with environmental change, likely explains some of the increasing influence of precipitation. Additional, indirect evidence suggests some role for increasing shrub density and changing precipitation regimes. Results from our long-term study demonstrate that the global phenomena of changing precipitation regimes, increasing frequency of extreme climatic events, and shrub encroachment are likely to have strong, interactive impacts in reorganizing ecological communities, with significant consequences for ecosystem dynamics.

Calcium as a limiting resource to insectivorous bats: can water holes provide a supplemental mineral source?

Data are presented on a bat assemblage captured among 10 water holes in Colorado over 5 years. The assemblage consists of Myotis ciliolabrum, M. evotis, M. lucifugus, M. thysanodes, M. volans, Eptesicus fuscus, Lasiurus cinereus, Lasionycteris noctivagans and Corynorhinus townsendii .R esults show that reproductive females and juveniles are captured in higher frequencies at water holes containing higher water hardness and that water hardness correlates highly significantly with dissolved calcium content. Also presented are laboratory test data on the stomach volume of Eptesicus fuscus that provide a model for understanding the effect of dissolved calcium content in water as a significant resource. These data indicate that water holes provide supplemental sources of calcium for bats not provided by diet.

Species composition and abundance of mammalian communities

Ecologists have long sought to understand the mechanisms underlying the assembly and structure of communities. Such understanding is relevant to both basic science and conservation-related issues. The macroecological approach to this problem involves asking scientific questions using a large number of communities in order to elucidate generalities in pattern and process. Such analyses are typically conducted using a substantial amount of data from a particular taxonomic group across a diversity of systems. Large community databases are available for a number of taxa, but no publicly available database exists for mammals. Given the logistical challenges of collecting such data de novo, compiling existing information from the literature provides the best avenue for acquiring the necessary data. Here, we provide a data set that includes species lists for 1000 mammal communities, excluding bats, with species-level abundances available for 940 of these communities. All communities found in the literature that included complete, site-specific sampling data, composed of species lists with or without associated abundances, were included in the data set. Most, but not all, sites are limited to species groups that are sampled using a single technique (e.g., small mammals sampled with Sherman traps). The data set consists of 7977 records from 1000 georeferenced sites encompassing a variety of habitats throughout the world, and it includes data on 660 mammal species with sizes ranging from 2 g to >500 kg. The complete data sets corresponding to abstracts published in the Data Papers section of the journal are published electronically in Ecological Archives at 〈http://esapubs.org/archive〉. (The accession number for each Data Paper is given directly beneath the title.)

EVALUATION OF METHODS USED TO ESTIMATE SIZE OF A POPULATION OF DESERT BIGHORN SHEEP (OVIS CANADENSIS MEXICANA )I N NEW MEXICO

Abstract Reliable estimates of size of populations are critical for successful management of translocated desert bighorn sheep (Ovis canadensis mexicana). As costs decrease and quality improves, remote cameras are increasingly used as a non-invasive tool to monitor populations of wildlife, but their efficacy has yet to be evaluated in a diversity of species and habitats. Here we investigate whether remote cameras, in combination with a simple mark-resight model, produce estimates of size of populations of desert bighorn sheep comparable to those derived from surveys conducted on the ground and using helicopters in the Fra Cristobal Range of south-central New Mexico. We determined that estimates of size of populations derived from remote cameras were comparable to those produced from direct observations obtained by surveys from helicopters and on the ground, that ca. 25 sequential samples of photographs produced comparable estimates of size of populations, but that photographs of single desert bighorn sheep dramatically lowered estimates of size of populations, and that placement of remote cameras on wildlife guzzlers in July produced the greatest number of photographs in the shortest time. Our results suggest that use of remote cameras may be an accurate, low-cost, and non-invasive means of estimating size of populations of desert bighorn sheep in New Mexico. Further research is warranted, ideally in tandem with ongoing surveys on the ground and using helicopters, in other management areas.

The Portal Project: a long-term study of a Chihuahuan desert ecosystem

This is a data paper for the Portal Project, a long-term ecological study of rodents, plants, and ants located in southeastern Arizona, U.S.A. This paper contains an overview of methods and information about the structure of the data files and the relational structure among the files. This is a living data paper and will be updated with new information as major changes or additions are made to the data. All data - along with more detailed data collection protocols and site information - is archived at: https://doi.org/10.5281/zenodo.1215988.