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Arid ecosystems are strongly limited by water availability, and precipitation plays a major role in the dynamics of all species in arid regions, as well as the ecosystem processes that occur there. However, understanding how biotic interactions mediate long-term responses of dryland ecosystems to rainfall remains very fragmented. We report on a unique large-scale field experiment spanning 25 yr and three trophic levels (plants, small mammal herbivores, predators) in a dryland ecosystem in the northern Chilean Mediterranean Region where we assessed how biotic interactions influence the long-term plant community responses to precipitation. As the most persistent ecological changes in dryland systems may result from changes in the structure, cover, and composition of the perennial vegetation, we emphasized the interplay between bottom-up and top-down controls of perennial plants in our analyses. Rainfall was the primary factor affecting the dynamics of, and interactions among, plants and small mammals. Ephemeral plant cover dynamics closely tracked short-term annual rainfall, but seemed unaffected by top-down controls (herbivory). In contrast, the response of the perennial plant cover to precipitation was mediated by (1) a complex interplay between subtle top-down (herbivory) controls that become more apparent in the long-term, (2) competition with ephemeral plants during wet years, and (3) an indirect effect of predators on subdominant shrubs and perennial herbs. This long-term field experiment highlights how climate-induced responses of arid perennial vegetation are influenced by interactions across trophic levels and temporal scales. In the face of global change, understanding how multi-trophic controls mediate dryland vegetation responses to climate is essential to properly managing the conservation of biodiversity in arid systems.

The matorral or Mediterranean scrub biome occurs within a narrow band of central Chile between approximately 30 and 38°S latitude. Bounded on the east by the Andean Cordillera and on the west by the Pacific Ocean, the area is characterized by a winter-wet, summer-dry climate, generally frost-free winters, and prolonged summer drought. A diverse flora includes many sclerophyllous shrubs, some drought-deciduous ones, and an herbaceous understory during winter and spring months. However, within the latter, exotic species which have become naturalized now make up a substantial proportion of the ephemeral flora. Matorral perennial shrub vegetation displays considerable endemicity, and is structurally convergent with Mediterranean scrub in California, Spain, and the Mediterranean Basin. Among higher vertebrates, herptiles, birds and small mammals exhibit broad geographic ranges in the matorral and lower species turnover between habitats (β-diversity) than in other Mediterranean scrub areas. Despite low taxonomic affinity, similar to perennial shrubs, there is convergence in major body types, feeding guilds and foraging techniques. Due to anthropogenic disturbance including clearing, fire, and extensive overgrazing/browsing, there are relatively few intact examples of undisturbed matorral left, and greater effort needs to be expended to preserve this highly unique biome. Long-term studies at a thorn scrub site on the northern edge of the matorral suggests that altered rainfall patterns have led to changes in the small mammal assemblage composition. Over time, such effects may also become manifest in the central Chilean matorral.

International audience; Long-term studies on rodents have been conducted for longer periods (up to 70 years) and more generations (upto 88 generations) than for most other mammalian taxa. These studies have been instrumental in furthering ourunderstanding of ecophysiology, social systems, and population and community processes. Studies on Africanstriped mice (Rhabdomys pumilio) revealed that basal blood glucose levels span a far greater homeostatic rangethan previously thought. Studies on American red squirrels (Tamiasciurus hudsonicus) demonstrated howendocrine pathways underlying phenotypic plasticity allow individuals to respond to different environments.Long-term studies on African striped mice, marmots (Marmota), tuco-tucos (Ctenomys sociabilis), and degus(Octodon degus) revealed that ecological constraints on dispersal are drivers of group formation in some speciesbut not others. Social flexibility, when the social system of an entire population can change due to individualschanging their social tactics, has been demonstrated in striped mice. Long-term studies on prairie voles (Microtusochrogaster) found that males and females often live in pairs, leading to subsequent studies of the neuralmechanisms underlying social monogamy. Long-term studies on other arvicoline rodents contributed more toour understanding of the factors influencing population dynamics than studies on any other mammalian order.While food availability and predation have been identified as factors influencing population dynamics, no singlefactor alone drives population dynamics in any species. We encourage researchers to incorporate manipulativeexperiments into long-term studies and to take integrative approaches to inform cross-disciplinary theory.

Desertification and climate change are degrading large areas of arid and semiarid habitat in many regions. In response, many countries have implemented revegetation programs, commonly using Atriplex nummularia, native to Australia. Although not intrinsically targeted at habitat restoration, these programs aim to restore (stabilize) erosional processes and provide livestock forage (usually goats, sheep). Few investigators have assessed the utility of these novel habitats for native fauna. In a recent, extensive survey of small mammal communities in lands revegetated with A. nummularia in north-central Chile, we captured a single animal, the marsupial (Thylamys elegans). We also captured no birds in our live traps and saw numerous darkling beetles in traps. These striking results contrasted with data from a nearby ungrazed park with natural vegetation where 10 small mammal species are known with total abundances ranging from 15 to 80 animals in similar sampling efforts. These revegetated lands provide poor habitat for native mammals, and we argue that revegetation efforts should include proactive risk assessment and cost-benefit analyses in a structured decision-making framework. In addition, managers should target increased plant species diversity to support broader biological diversity in addition to the need to control erosion. Although our work has focused on revegetation with Atriplex, numerous other plant species have been intentionally introduced to arid lands, usually for economic reasons; many of these, like Atriplex, have unintended consequences for native biota.

In 1989, we initiated a long-term field experiment in a semiarid thorn scrub community in north-central Chile. We posited that biotic interactions, particularly predation, interspecific competition, and herbivory assumed a primary top-down role in affecting small mammals and annual plants here. Using a multi-factorial design we selectively excluded vertebrate predators (principally carnivores and raptors) and a large small mammal herbivore, the degu (Octodon degus), from replicated 0.56 ha exclosures located in a valley near the coast in Bosque Fray Jorge National Park. Evidence initially supported effects of predator exclusion on O. degus but not for other small mammals in the assemblage (e.g., Phyllotis darwini, Abrothrix olivaceus). Subsequent years of monitoring have documented that predation has temporary effects on degu numbers, but that populations of this and other small mammals are much more strongly influenced by environmental bottom-up factors (i.e., rainfall). Further, our experimental manipulation has provided no evidence for negative interspecific competition effects on numbers of any small mammal in this assemblage. Degu exclusions, however, have had negative indirect effects on exotic annuals; native annuals appear to outcompete exotics especially during drought years The effect is magnified in all-small mammal exclusions. Since about 2002, selective exclusions of lagomorphs and small mammals have resulted in changes in cover of some perennial shrubs. Also notable has been a fundamental shift in the small mammal composition following the last major El Niño Southern Oscillation (ENSO) event in 2000?2002; degus now comprise a majority of small mammal biomass in the assemblage, and their numbers have become more stable and less temporally variable. This appears to have been caused by a shift in rainfall periodicity from strong interannual fluctuations in response to periodic ENSOs, to a more equitable pattern with more consistent annual rainfall. This represents one of the first documented cases of system-wide biotic phase shifts to a relatively modest change in rainfall regime. This may be indicative of ongoing climate change in the Chilean semiarid region, and we expect that further changes in the community will occur if those trends continue. Fil: Meserve, Peter L.. University of Illinois; Estados Unidos Fil: Kelt, Douglas A.. University of California; Estados Unidos Fil: Gutiérrez, Julio R.. Universidad de La Serena; Chile Fil: Previtali, Maria Andrea. Universidad Nacional del Litoral. Facultad de Humanidades y Ciencias. Departamento de Ciencias Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina Fil: Milstead, W. Bryan. U.S. Environmental Protection Agency; Estados Unidos

In 2003, we initiated a sampling protocol for arthropods as part of long-term field experiment in a semiarid thorn scrub community in north-central Chile. We utilized pitfall and Malaise traps to sample terrestrial and volant arthropods, respectively. Inventories were conducted for 4 days and nights monthly. We posited that arthropod abundance and biomass would track environmental changes such as high rainfall often due to El Nino Southern Oscillations (ENSOs). Peaks in both abundance and biomass for terrestrial and volant arthropods were in similar months (spring–early summer; August–November); arthropods also tracked high rainfall years in 2004, 2006, and 2011, due mostly to increases in a few dominant groups, i.e., tenebrionid beetles (Coleoptera) in terrestrial sampling, and moths (Lepidoptera: Noctuidae, microlepidoptera) in aerial sampling. However, the same groups increased dramatically in 2008 which was a below-average rainfall year. Numerical decreases in late summer-fall months (January–April) were more abrupt for terrestrial arthropods than for volant ones. Both terrestrial and volant arthropods reached their lowest levels in winter months (June–July). Some evidence suggests long-term shifts in the composition of volant taxa. Arthropods likely are important prey items for insectivorous reptiles (i.e., lizards), birds, and an insectivorous small mammal, the elegant mouse opossum ( Thylamys elegans ), and future efforts are being directed towards examining the evidence for correlated changes in those consumers with arthropod abundance and biomass.

Models of plant–plant interactions suggest that nurse plants are critical for the maintenance of biodiversity and ecosystem functions in arid and semiarid lands. At the community scale, however, empirical support of this idea is limited and context-dependent. Following on a preliminary work which suggested that a dominant shrub in north-central Chile ( Porlieria chilensis ) had nurse plant effects, we tested the effects of this and two other shrubs ( Adesmia bedwellii and Proustia cuneifolia ) on community biomass production, species density, and species composition of ephemeral plants in the semiarid scrub of the Bosque Fray Jorge National Park (Chile) over four consecutive years. We tested for main and interactive effects of shrubs and precipitation on total biomass production and species density of ephemeral plant communities using Generalized Linear Mixed Models (GLMM). To analyze the effects of shrubs and precipitation on species composition we used Canonical Correspondence Analysis (CCA) and t-value biplot analysis. Total biomass production increased significantly with precipitation and was consistently lower beneath shrub canopies, particularly under A. bedwellii and P. chilensis . Although ephemeral plant species density generally was higher in open areas, differences between open and shrub canopy samples diminished with increasing precipitation. Finally, despite significant differences in ephemeral plant species composition between open areas and shrub canopies, we found no evidence of shrub species-specific effects. In conclusion, our results do not support a classical nurse plant syndrome in the semiarid scrub of the Bosque Fray Jorge National Park although shrubs can increase local diversity by favoring some ephemeral plant species that are absent in open areas.

Patterns in rainfall and soil water availability are considered to be the main drivers governing arid and semiarid ecosystems. While the mechanisms by which water limits aboveground net primary production has been widely explored, few long-term studies have examined interactions between precipitation, soil resources, plant communities, and soil microbial communities; these may be critical to understanding soil biogeochemical cycles and above- and belowground interactions. We capitalized on a long-term biotic manipulation (exclusion of small mammal herbivores from replicate plots) and long-term variation in rainfall to assess how precipitation, small mammals, and shrub cover act directly and interactively to influence the spatial and temporal distribution of soil microorganisms, a key first step to understanding soil biogeochemical cycles. We measured the abundance of arbuscular mycorrhiza (AM), soil fungi, soil bacteria, and soil physicochemical characteristics over 10 consecutive years in a semiarid thorn scrub community in north–central Chile; we sampled two microhabitats (under shrub cover, and in open spaces between shrubs colonized by ephemeral plants), and in plots with or without the presence of native small mammals, the main herbivores in this environment. Annual rainfall ranged widely (11–356 mm) in this period and was the primary factor affecting abundance of AM root colonization and soil microbes. While the percentage of root length with AM was higher in dry compared to wet years, free-living soil bacteria and fungi were more abundant during wet years. All microorganisms were more abundant in the resource islands beneath the shrubs compared to open microhabitat between shrubs, although the relation between soil biota and the concentration of some particular nutrients was negative. These patterns were modulated by the presence of small mammals, which enhanced root colonization by AM fungi, particularly for ephemeral plants, but which were negatively associated with soil fungi abundance. The abundance of soil bacteria showed a more complex response to the presence of small mammals and was dependent on microhabitat and year. The spatial and temporal heterogeneity of soil resources and the activity of small mammals are important modulators of subterranean biotic responses to rainfall, the primary factor affecting soil microbiota abundance in this semiarid ecosystem.

The avifauna of Chile is relatively depauperate, comprising 469 extant species, of which 213 are terrestrial. However, the Coquimbo Region presents a broad ecological transition from the hyperarid Atacama Desert to the north, and the more mesic Chilean Mediterranean region of central Chile, resulting in relatively high species diversity. Approximately 130 species are found here, 8 of which are endemic to Chile although not to this region. Bosque Fray Jorge National Park is a 9959 ha Biosphere Reserve dominated by matorral habitat and hosting up to 123 bird species. Through avian surveys and banding over nearly a decade we have documented 63 terrestrial species and discerned predictable seasonal and interannual structure to avian assemblages, at least through an extended dry period. Recent studies in the matorral habitats of the park indicate seasonal patterns that fall into 4 patterns: year-round residents, winter visitors, summer breeders, and transients. Short-term banding studies demonstrate co-occurring wintering and breeding cohorts among species of Sierra-finches (Phrygilus) in the park; such assemblages and dynamics are reminiscent of North American Mediterranean avian assemblages and pose interesting ecological comparisons. In this period of surveys there appears to have been a gradual transition of the avifauna that may be a response to anthropogenic influence and/or climate change. Research on the foraging behavior of 2 insectivorous species indicate that one of these is convergent on better-known North American taxa while the other clearly is not; these efforts suggest useful avenues for further comparative research. A remarkable coevolutionary association between the Chilean Mockingbird (Mimus thenca) and endoparasitic mistletoes (Tristerix) provides insight into potential convergent ecologies in desert regions with different evolutionary histories. Less than 1% of the park comprises temperate forest remnants that subsist due to extensive water input from fog. Research in these remnants has emphasized the role of habitat fragmentation on avian assemblage composition and on reproductive ecology by forest-dependent species. The avifauna here comprises a subset of that found in intact Valdivian rainforest to the south, and forest remnant size alone explains over 90% of the variation in species numbers. One species has been particularly well studied; the Thorn-tailed Rayadito (Aphrastura spinicauda) is more abundant and has higher nestling survival in larger fragments. We summarize other work on stress responses and variation in song structure in this species. Finally, the role of birds in tree recruitment here has important implications in the face of a recent history of reduction in sizes of forest remnants; numerous birds consume the fruit of the dominant tree, olivillo (Aextoxicon punctatum), but they fail to promote successful recruitment because they defecate viable seeds in locations that provide poor survival of seedlings. Ornithological research in Chile is undergoing a modest renaissance, and while dryland avifaunas are characterized more by what is not known and has yet to be studied than by actual ecological understanding, they provide a baseline for many exciting studies ranging from natural history to the role of migration to comparative dynamics of independent lineages in North and South America.

Scientists are increasingly interested in the evolutionary responses of organisms to unpredictable, variable, and extreme climate changes. In semiarid environments, inter-annual variability in the frequency and amount of rainfall affects both the growth and recruitment of plant species, especially annuals. In these inherently variable environments, individual selection should favor demographic responses that spread the risk of mortality over time and enhance long-term reproductive success (i.e., bet-hedging strategies). However, the same processes that allow the persistence and recruitment of native species could facilitate the introduction and establishment of exotics. We assessed whether native and exotic annuals in semiarid Chile displayed similar or contrasting bet-hedging traits, and discuss mechanisms of coexistence of both types of species and their demographic variation under interannual rainfall variability driven by El Nino Southern Oscillation (ENSO). We analyzed a proxy of long-term fitness, i.e., the variability of seed density over 17 years, for the two most common native and two exotic annual plant species present in the study area. We experimentally tested whether the quality of the maternal environment (soil water supply in a given year) had an extended effect (e.g. the next year) on the proportion of seed germination or on the mean and/or variability of seed size and seed dormancy. Results showed that native and exotic species in this annual plant assemblage displayed contrasting bet-hedging strategies as evolutionary responses to variable rainfall. Although rainfall variability promotes the evolution of bet-hedging strategies, the nature of these strategies varies across species, presumably to minimize competitive exclusion. In semiarid Chile, the success of two exotic ephemerals that are components of a diverse community of native annual species seems to reflect bet-hedging germination strategies that complement rather than compete with those expressed in dominant natives.

Motivation The BioTIME database contains raw data on species identities and abundances in ecological assemblages through time. These data enable users to calculate temporal trends in biodiversity within and amongst assemblages using a broad range of metrics. BioTIME is being developed as a community-led open-source database of biodiversity time series. Our goal is to accelerate and facilitate quantitative analysis of temporal patterns of biodiversity in the Anthropocene. Main types of variables included The database contains 8,777,413 species abundance records, from assemblages consistently sampled for a minimum of 2 years, which need not necessarily be consecutive. In addition, the database contains metadata relating to sampling methodology and contextual information about each record. Spatial location and grain BioTIME is a global database of 547,161 unique sampling locations spanning the marine, freshwater and terrestrial realms. Grain size varies across datasets from 0.0000000158 km2 (158 cm2) to 100 km2 (1,000,000,000,000 cm2). Time period and grain BioTIME records span from 1874 to 2016. The minimal temporal grain across all datasets in BioTIME is a year. Major taxa and level of measurement BioTIME includes data from 44,440 species across the plant and animal kingdoms, ranging from plants, plankton and terrestrial invertebrates to small and large vertebrates. Software format .csv and .SQL., Global Ecology and Biogeography, 27 (7), ISSN:1466-822X, ISSN:1466-8238

Understanding the nature of faunal assembly and community structure remains central to ecology. Research in North American deserts and some tropical forests provides evidence of energetic compensation and zero-sum dynamics, suggesting that species in some natural assemblages may be replaced with limited impact on ecosystem function. Experimental removal of a dominant small mammal (degu, Octodon degus) from replicate plots in semiarid coastal thorn-scrub habitat in north-central Chile revealed no evidence for energetic or functional compensation; energy consumption remained significantly lower on degu exclusions relative to control plots after 17 years of exclusion. This occurred in spite of the fact that the geographic species pools for South American sites generally are similar in size to those of most North American sites (mean and median number of species, 16.3 and 21.5 vs. 21.0 and 20, respectively). A macroecological assessment of energetically equivalent species at 394 arid sites in North America, t...

South America spans about 44° latitude, covers almost 18 million km(2) , and is second only to Africa in continental mammal species richness. In spite of this richness, research on the status of this fauna and on the nature and magnitude of contemporary threats remains limited. Distilling threats to this diverse fauna at a continental scale is challenging, in part because of the limited availability of rigorous studies. Recognizing this constraint, we summarize key threats to small mammals in South America, emphasizing the roles of habitat loss and degradation, direct persecution, and the increasing threat of climate change. We focus on three regional 'case studies': the tropical Andes, Amazonia and adjacent lowland regions, and the southern temperate region. We close with a brief summary of recent findings at our long-term research site in north-central Chile as they pertain to projected threats to this fauna. Habitat alteration is a pervasive threat that has been magnified by market forces and globalization (e.g. extensive agricultural development in Amazonia), and threatens increasing numbers of populations and species. Climate change poses even greater threats, from changes in rainfall and runoff regimes and resulting changes in vegetative structure and composition to secondary influences on fire dynamics. It is likely that many changes have yet to be recognized, but existing threats suggest that the future may bring dramatic changes in the distribution of many mammal taxa, although it is not clear if key habitat elements (vegetation) will respond as rapidly as climatic factors, leading to substantial uncertainty. Climate change is likely to result in 'winners' and 'losers' but available information precludes detailed assessment of which species are likely to fall into which category. In the absence of long-term monitoring and applied research to characterize these threats more accurately, and to develop strategies to reduce their impacts, managers already are being faced with daunting challenges. As the line between 'pure' and 'applied' research blurs in the face of converging interests of scientists and society we hope that solutions to these critical issues will be incorporated in addressing anticipated conservation crises.

The species composition of the Chilean avifauna is well-defined taxonomically but is not well known ecologically. We sampled avian communities at a biosphere reserve in coastal north-central Chile in three seasons over six years (18 surveys total) and characterized them in terms of community structure and composition. The avifauna (S = 56 species) was dominated by insectivores (S = 20), carnivores (S = 14), and granivores (S = 13), with lesser contributions by omnivores (S = 5), nectarivores (S = 2), folivores (S = 1), and one vagrant piscivore. The fauna varied greatly between summer and winter, and in most years the breeding season also was distinct. Eighteen species constituted a core group of residents observed in nearly all surveys, but at least 15 species were nomadic or migratory. Our site supported more insectivorous species in winter but more granivores and omnivores in the breeding season, although this observation may be confounded by species' detectability. The structure of the set o...

The abundance of exotic plants is thought to be limited by competition with resident species (including plants and generalist herbivores). In contrast, observations in semiarid Chile suggest that a native generalist rodent, the degu (Octodon degus), may be facilitating the expansion of exotic annual plants. We tested this hypothesis with a 20-year data set from a World Biosphere Reserve in mediterranean Chile. In this semiarid environment, rainfall varies annually and dramatically influences cover by both native and exotic annual plants; degu population density affects the composition and cover of exotic and native annual plants. In low-rainfall years, cover of both native and exotic herbs is extremely low. Higher levels of precipitation result in proportional increases in cover of all annual plants (exotic and native species), leading in turn to increases in degu population densities, at which point they impact native herbs in proportion to their greater cover, indirectly favoring the expansion of exotic plants. We propose that bottom-up control of consumers at our site results in top-down indirect facilitation of invasive annual herbs, and that this pattern may be general to other semiarid ecosystems.

Global climate change (GCC) can have profound effects on species whose ecology is governed primarily by climatic factors. The ecology of small mammals inhabiting semiarid Chile is strongly affected by the El Niño Southern Oscillation (ENSO). During La Niña events in this area, dry conditions prevail and species may disappear from the thorn-scrub habitat. Conversely, El Niño events bring high rainfall, and associated pulses of food trigger small-mammal population increases. We used capture-mark-recapture to study responses of the degu (Octodon degus), a dominant small mammal, to variation in rainfall over 18 years. In response to a recent trend toward wetter conditions, degus reached record-high densities and maintained more stable numbers in the area. Underlying mechanisms involved variation in adult survival, juvenile persistence, and fecundity linked to rainfall changes during consecutive years (i.e., rainfall phases). During prolonged droughts, degus had low survival and produced fewer offspring, with low persistence. Following high rainfall, these parameters reversed; consecutive wet years resulted in further increases. Weak declines in fecundity and adult survival and high persistence of juveniles explained delayed responses to deteriorating conditions in initial dry years. If GCC leads to increased frequency of El Niño events, we anticipate greater numerical dominance of degus in semiarid Chile and possible range expansion. Furthermore, degus have strong impacts on other small mammal and some plant species, are important prey species, and are agricultural pests and disease reservoirs. Hence, GCC has the potential to dramatically influence their ecology in northern Chile and to have cascading effects on other components of this system.

We investigated the effects of fluctuating prey numbers on the foraging strategies and potential mechanisms for coexistence of 2 sympatric predators, coyotes (Canis latrans) and red foxes (Vulpes vulpes), in a heterogeneous environment in northeastern Illinois. We quantified the availability of mammalian and avian prey across different habitats, analyzed scats collected along standardized routes for occurrence of prey items, and estimated the number and biomass of vertebrate prey consumed. Abundances of the most frequently consumed prey (voles, rabbits, and mice) differed significantly over time, especially in relation to an ice storm that occurred during the study. Coyotes and red foxes tended to select voles and rabbits in number, rabbits in biomass, and incorporated greater numbers and biomass of other prey such as deer, pheasants, and sciurids after the ice storm. Log-linear analyses indicated that both coyotes and red foxes exhibited switching behavior, with differential shifts among the number and biomass of alternative prey they consumed. Hence, foraging strategies of coyotes and red foxes appeared to be a combination of prey selectivity and switching behavior. Our study suggests that competition between coyotes and red foxes for similar primary prey species and limited environments to exploit at the urban–rural interface may contribute to displacement of red foxes by coyotes.

Lower-elevation habitats of north-central Chile are characterized by semiarid vegetation that is strongly influenced by rainfall related to El Nino Southern Oscillation (ENSO) events. During the ENSO warm phase (i.e., El Nino), heavy rains occur resulting in small mammal irruptions or ratadas. During prevailing drier periods, pronounced droughts result in reductions in small mammal densities and local extinctions of some species. Within the dominant thorn-scrub habitat of a national park, we identified 2 other habitat types, aguadas (riverine shrublands) and fog-forest patches that serve as refuges for small mammals during dry years. We divide small mammal species of the thorn scrub into 2 groups: core species (Octodon degus, Phyllotis darwini, Abrothrix olivaceus, and Thylamys elegans) maintain populations at all times, whereas opportunistic species (Oligoryzomys longicaudatus and A. longipilis) are present only after rains. The latter group appears to maintain refuge populations in aguadas and fog forests and to opportunistically exploit the thorn scrub when conditions are favorable. Aguadas also may play an important role in the persistence of less-common species, such as Octodon lunatus and Abrocoma bennetti. Despite being small and patchily distributed, aguadas are important for the maintenance of regional biodiversity.

The warm phase of El Niño-Southern Oscillation (ENSO) events results in greatly elevated rainfall in north-central Chile, with dramatic effects on small mammals and vertebrate carnivore abundances. In ensuing cool phases of ENSO, plant cover decreases, followed by small mammal densities, in turn affecting the resource availability for their predators. Wild carnivores such as foxes are one of the main predators of small mammals; when the latter decline, foxes could exhibit functional responses, increasing their consumption of domestic livestock. To our knowledge, the influence of native prey abundance on livestock predation has not been assessed. We hypothesize that periods of scarce native prey increases conflicts between carnivores and farmers outside protected areas, especially during drought years. From 1990 to 2005 we used live trapping to determine monthly density of small mammals in a national park (Bosque Fray Jorge National Park, BFJNP) in north-central Chile; rainfall was also monitored. We calculated an index of predation as the number of sheep predated by foxes annually on one farm (encompassing ca. 45,000 ha) located in the vicinity of BFJNP. Path analysis was carried out to assess factors influencing sheep predation by wild foxes. Factors included precipitation and small mammal density. Small mammal density correlated positively with two years moving average of rainfall. Sheep predation by foxes increased after of two years of low rainfall. Our findings suggest that wild carnivores employ functional responses in response to varying prey availability, shifting from wild to domestic prey during periods of drought, which could have important conservation and management implications Fil: Acosta Jamett, G.. Universidad Austral de Chile; Chile Fil: Gutiérrez, Julio R.. Universidad de La Serena; Chile Fil: Kelt, D. A.. University of California; Estados Unidos Fil: Meserve, P. L.. University of Illinois; Estados Unidos. University of Idaho; Estados Unidos Fil: Previtali, Maria Andrea. Universidad Nacional del Litoral. Facultad de Humanidades y Ciencias. Departamento de Ciencias Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina

Fundamentally, El Niño Southern Oscillation (ENSO) is a climatic and oceanographic phenomenon, but it has profound effects on terrestrial ecosystems. Although the ecological effects of ENSO are becoming increasingly known from a wide range of terrestrial ecosystems (Holmgren et al., 2001), their impacts have been more intensively studied in arid and semiarid systems. In this brief communication, we summarize the main conclusions of a recent symposium on the effects of ENSO in these ecosystems, which was convened as part of the First Alexander von Humboldt International Conference on the El Niño Phenomenon and its Global Impact, in Guayaquil, Ecuador, from 16–20 May 2005. Participants in the symposium shared results and perspectives from research conducted in North and South America and Australia, regions where the ecological effects of ENSO have been studied in depth. Although the reports covered a wide array of organisms and ecological systems (Fig. 1), a recurring theme was the strong increase in rainfall associated with ENSO events in dry ecosystems (during the El Niño phase of the oscillation in the Americas and the La Niña phase in Australia). Because inter-annual variability in precipitation is such a strong determinant of productivity in arid and semiarid ecosystems, increased ENSO rainfall is crucial for plant recruitment, productivity and diversity in these ecosystems. Several long-term studies show that this pulse in primary productivity causes a subsequent increase in herbivores, followed by an increase in carnivores, with consequences for changes in ecosystem structure and functioning that can be quite complex.

Aim This study aims to evaluate the relative importance of birds, small mammals, and ants as seed predators at a semi-arid site in northern Chile. Location Northern Chile, in Parque Nacional Bosque Fray Jorge (30°41′ N, 71°40′ W, c. 80 m elevation). Methods We studied the relative abilities of birds, small mammals, and ants to find and remove millet seeds either singly (i.e. background seed removal) or in bulk. Single seeds were set in shallow depressions in Plexiglas trays which were established in long and arbitrary transects, and were available either to birds (diurnally) or small mammals (nocturnally) or were covered by hardware cloth and therefore available only to ants. Bulk removal was evaluated with seeds in Petri dishes that also were established in long and arbitrary transects, and trays were either open diurnally (birds) or nocturnally (small mammals); a third set of trays was covered with hardware cloth cages to excluded vertebrates, and ants were given access to Petri dishes with twigs that were arranged across the edge of the dishes. All experiments lasted four days and nights, and trays and dishes were checked and replenished as needed in the morning and evening. In the former study vertebrate consumption was determined as the mean number of seeds removed from trays (within a given transect) minus the number removed from ant-only trays. Because ants were rarely seen in vertebrate access Petri dishes, however, we did not correct consumption there. Treatments were compared using repeated measures mixed model analysis of variance. In addition to evaluating patterns within this community, we compared our results against those obtained in similar studies in various arid regions. Results Diurnal seed consumption was significantly greater than nocturnal seed consumption, which in turn was significantly greater than consumption by ants. Diurnal consumption was highly seasonal, evidently corresponding to the seasonal arrival and departure of migratory birds. In general, South American sites exhibit much lower levels of seed predation than sites in the northern hemisphere, but removal at our site appears to be much greater and more strongly avian-dominated than at other sites in South America. Our results are consistent with predictions based on a hypothesis relating precipitation to seed predictability. Main conclusions Both birds and small mammals were much more important seed consumers at our site than elsewhere in South America, whereas ants have been relatively unimportant at all South American sites studied to date. Although the dominant seed consumers differ across sites, overall levels of seed removal appear similar in South America and Australia, and substantially lower than reported from sites in the northern hemisphere and Africa. Resumen Objetivo El objetivo de este estudio es evaluar la importancia relativa de aves, pequenos mamiferos y hormigas como depredadores de semillas en un sitio semiarido del norte de Chile. Localidad En el norte de Chile, en el Parque Nacional Bosque Fray Jorge (30° 41′ N, 71° 40 W, 80 m.s.n.m.). Metodos Estudiamos las capacidades relativas de aves, pequenos mamiferos y hormigas para encontrar y remover semillas de mijo tanto individualmente (es decir, remocion de la semilla del fondo) como en paquetes. Las semillas individuales se fijaron en depresiones superficiales en bandejas de Plexiglas que fueron puestas en transectos largos y arbitrarios, y que estaban disponibles para las aves (en el dia) o los pequenos mamiferos (en la noche), o fueron cubiertas por una malla tipo harnero y por lo tanto disponibles solamente para las hormigas. La remocion de paquetes fue evaluado con semillas en placas Petri que tambien fueron establecidas en transectos largos y arbitrarios, y las bandejas fueron abiertas durante el dia (para aves) o durante la noche (para pequenos mamiferos); un tercer grupo de bandejas se cubrio con jaulas de malla tipo harnero para excluir a los vertebrados, y a las hormigas se les dio acceso a las placas Petri con ramitas que se pusieron en los bordes de las placas. Todos los experimentos duraron cuatro dias y cuatro noches, y las bandejas y las placas se revisaron y reabastecieron de acuerdo a lo necesario en la manana y la tarde. En el estudio anterior el consumo por los vertebrados se determino como el numero promedio de las semillas removidas de las bandejas (dentro de un transecto) menos el numero removido de las bandejas con acceso a las hormigas solamente. Debido a que las hormigas fueron raramente vistas en las placas Petri con acceso a los vertebrados, sin embargo, no corregimos el consumo alli. Los tratamientos se compararon usando el modelo mixto de analisis de varianza para medidas repetidas. Ademas, para evaluar los patrones dentro de esta comunidad, comparamos nuestros resultados con otros obtenidos en estudios similares en varias regiones aridas. Resultados El consumo de semillas durante el dia era significativamente mayor que el de la noche, lo que en cambio fue significativamente mayor que el consumo por las hormigas. El consumo diurno fue altamente estacional, lo que evidentemente corresponde a la llegada y salida estacional de aves migratorias. En general, las localidades sudamericanas exhiben niveles de depredacion de semillas que son mucho mas bajas que en sitios del hemisferio norte, pero la remocion en nuestro sitio parece ser mucho mayor y dominado por aves que en otras localidades de America del sur. Nuestros resultados son consistentes con las predicciones basadas en una hipotesis que relaciona la precipitacion con la prediccion de semillas. Conclusiones principales Tanto las aves como los pequenos mamiferos fueron consumidores de semillas mucho mas importantes en nuestro sitio que en otros sitios de Sudamerica, mientras que las hormigas han sido relativamente poco importantes en todos los sitios sudamericanos estudiados hasta la fecha. Aunque los consumidores de semillas dominantes difieren entre sitios, los niveles totales de remocion de semillas parecen similares en America del Sur y Australia, y substancialmente mas bajos que los documentados para sitios del hemisferio norte y Africa.

We report on the foraging behavior of three small-mammal species over 2½ years using experimental foraging trays. Trays provisioned with oat seed were set out in the field at dawn and dusk, and the amount of seed consumed (with re-provisioning) was determined over three consecutive nights and days. Experiments simultaneously evaluated the role of lunar phase, season, and microhabitat (shrub vs. open); additionally, artificial exclosures (∼0.56 ha) were employed to evaluate the influence both of mammalian and avian predators and of a dominant competitor species, the large diurnal degu (Octodon degus). Other principal small mammals included Darwin's leaf-eared mouse (Phyllotis darwini) and the olive field mouse (Akodon olivaceus). Trays were enclosed by hardware-cloth cages with either small or large holes in the side to exclude avian consumers and provide selective access to all small mammals (large holes) or to exclude the largest species (small holes). Small-mammal population sizes varied greatly through...

We investigated predation risk and competition as they affected small-mammal foraging behavior in semiarid north-central Chile. Giving-up densities (GUD) of seeds were used to measure the foraging activity of the three most common small mammals at the site: degu (Octodon degus), Darwin's leaf-eared mouse (Phyllotis darwini), and the olivaceous field mouse (Akodon olivaceus), under shrubs (cover) and in the open on predator-excluded and competitor-excluded (Octodon) plots. Experiments were conducted during both new and full moons. Monthly small-mammal censuses using standard mark–recapture techniques provided data on movement, reproduction, and long-term fluctuations in density between 1989 and 1994. Diurnal Octodon foraged more (had lower GUD) in the absence of predators (although this was confounded by a numerical increase resulting from predator exclusion), and foraged more under shrubs than in the open. However, the lack of a significant cover × predator exclusion interaction and thermoregulation studi...

Since 1989, effects of biotic interactions including predation and herbivory have been examined in a replicated experimental study in a north-central Chilean semiarid thorn scrub community. Strong responses of small mammals and plants to El Nino Southern Oscillations (ENSO) have also been documented suggesting that ''bottom- up'' factors related to high rainfall are important. To simulate increased primary productivity effects on small mammals, ad lib rabbit pellet additions were initiated in mid-1997 on unfenced grids near the experimental complex. Following the 1997 El Nino event with three times normal precipitation, numbers of small mammals during pre-addition months and the first treatment year were similar on control and food addition grids. During the second year (1998 -1999), a period of severe drought, food additions had significant positive effects on numbers of two predominantly herbivo- rous ''core'' (resident) species, Octodon degus and Phyllotis darwini, and an omnivo- rous ''quasi-core'' (resident but highly fluctuating) species, Akodon oliaceus; however, all three species declined towards the end of the second treatment year. Two ''opportunistic'' (temporarily resident) species, Abrothrix longipilis (an insectivore) and Oligoryzomys longicaudatus (a granivore), showed no responses to food addi- tions. An insectivorous marsupial, Thylamys elegans (also a ''core species''), had significantly lower numbers on food addition grids. Changes in body weight distribu- tions and proportions of reproductive individuals particularly in O. degus indicate in situ responses. Whereas no differences in residency, numbers of stations visited, and trappability were observed, energy compensation ratios greater than one suggest significant immigration in the second year. Thus, food additions elicited strong responses by herbivorous/omnivorous ''core'' and ''quasi-core species'' whereas they had no effects on ''opportunistic species''. These results reinforce the view that ''bottom-up'' factors influencing food availability exert prevailing control on numer- ically important small mammal species by temporarily increasing carrying capacity, and that ''top-down'' factors (i.e., biotic interactions) become important when small mammal numbers are at or near their carrying capacity. Spatial dynamics may be important in explaining declines of species populations exhibiting initially positive responses to food additions.

Movements and interactions of Chilean culpeo foxes ( Pseudalopex culpaeus ) were studied in a semi-arid region characterized by periodic droughts. Annual home ranges of adult foxes averaged 3.7 km2 ( SE = 1.1), and home ranges of females were larger than those of males. Human-dominated habitats were included in 85% of estimated home ranges. Home range overlap averaged 27%. Analyses of spatial interactions indicated that two pairs of males shared the same ranges. Temporal interactions suggested a lack of synchrony in individual movement patterns, but foxes were most active during night. Populations of prey and the culpeo fox declined as a consequence of drought.

Small mammals were studied in two southern Chilean temperate rainforests in the precor-dillean Andes during 2 low-rainfall years following the 1982 El Nino event. Forests had somewhat different levels of canopy, shrub, and herbaceous cover, and species richness of trees but most of the same plants. Most captures were of four sigmodontine rodents, Akodon olivaceus, Abrothrix longipilis, Abrothrix sanborni , and Oligoryzomys longicaudatus ; five other species and a putative hybrid were recorded. Maximum numbers were in January–July (late summer to winter) and lower numbers in August–December (late winter to early summer). All species had seasonal reproduction in September–April (spring to autumn). A. olivaceus and A. longipilis generally were long-lived, whereas survival rates were low for O. longicaudatus . Responses after the 1982 El Nino were small, and some populations increased during 1984. Populations of A. olivaceus fluctuated more than those of A. longipilis ; those of A. sanborni were low and O. longicaudatus was sporadic and irruptive. Lower-elevational Chilean and precordilleran Argentine forests have similar species composition, but differences in demography and dominance of the former by more widespread, omnivorous A. olivaceus , animalivorous-fungivorous Abrothrix , and granivorous O. longicaudatus . Opportunities for immigration may explain greater homogeneity of populations of small mammals in Chilean rainforests relative to Argentine ones. Although responses to El Nino and subsequent droughts were weak, flowering episodes of bamboo ( Chusquea ) can have strong effects due to increased availability of food.

Micro-organisms and nutrients were determined in soil samples (top 20 cm) collected underneath and outside the canopy of Adesmia bedwellii in mid fall (April 1997), after 8 months of drought, and in mid spring (October 1997) after heavy winter rains associated with the 1997-ENSO in a Chilean coastal desert site. Bacteria and fungi were two orders of magnitude higher in mid spring, but no seasonal effects were detected for chemical parameters. Micro-organisms, organic matter and nitrogen content were significantly higher underneath shrub canopies, especially in mid fall. Micro-organism abundances were positively correlated with nitrogen levels and soil moisture.

We monitored the cover and seed bank response of shrubs, perennial herbs, and ephemeral plants to experimental exclusion of both the principal rodent herbivore, Octodon degus, and its vertebrate predators from 1989 to 1994 in a semiarid Chilean mediterranean site. Although both richness and species composition of the plant community at the study site were largely determined by abiotic factors (mainly rainfall and soil nutrients), predator and herbivore exclusion had significant effects on the relative abundance of several plant species. Experimental exclusion of herbivores was associated with increased cover of some shrubs and a perennial grass, and decreased cover and seed densities of several ephemerals, especially those exotic or restricted to areas underneath shrubs. Herbivores apparently reduced shrubs through browsing and indirectly affected herb cover and seed densities by opening up areas under shrubs and/or modifying physical and chemical conditions of the soil. Plant responses to predator exclusion were less clear. Nevertheless, higher cover of some shrubs and ephemerals in the presence of predators suggests tritrophic effects through changes in small mammal densities and/or foraging behavior.

The role of biotic interactions including vertebrate predation and interspecific competition was studied among members of a semiarid small mammal assemblage in a long-term field manipulation in north central Chile. Fences and netting selectively excluded mammalian and avian predators, and a putative rodent competitor, the degu (Octodon degus), from large, replicated grids. Small mammal populations were censused monthly over >4 yr, and effects of predator and degu exclusions on numbers and survival of small mammals were assessed with repeated measures ANOVAs. Marginally significant predator exclusion effects were detected on 0. degus, and highly significant year X predation interactions in both wet and dry seasons; degu survival (= persistence) was also significantly longer on exclusion grids. Predation had significant effects on numbers of Phyllotis darwini, and a significant month X predator interaction existed in the wet season; survival was also sig- nificantly higher on predator exclusion grids. There was a marginally significant year X competitor interaction in the dry season for this species. Akodon olivaceus had significant month X predator and month x competitor interactions in the wet season only; survival was significantly longer on degu exclusion grids. An irruptive species, Oligoryzomys lon- gicaudatus, showed no significant predator or competitor effects in 1991-1992; however, survival was significantly longer on predator + competitor exclusion (vs. control) grids. An uncommon species, Abrothrix longipilis, had marginally nonsignificant time x com- petitor interactions but no treatment differences in survival. Finally, a second uncommon rodent, Abrocoma bennetti (not analyzed numerically) had significantly longer survival on predator exclusion grids with degus. Degus and P. darwini were significantly overrepre- sented (relative to availability) in diets of culpeo foxes (Pseudalopex culpaeus) and three nocturnal owls, respectively, whereas A. bennetti was significantly overrepresented in pred- ator diets generally. Vertebrate predation has pervasive effects on some species that, how- ever, may be related to their intrinsic demographic characteristics. Competition may be mediated by subtle behavioral interactions among assemblage members. Long-term studies are necessary to elucidate the role of biotic and abiotic factors in semiarid environments.

Competition has been shown to be an important factor in natural systems. Yet, its effect on community structure remains poorly understood and is often disputed. Null models have been employed by researchers in recent years, but these generally suffer from a lack of power estimation and unclear distinction between statistical significance and biological importance. Models that employ an appropriate alternative hypothesis allow for power estimates and for quantitative evaluation of the effects of competition. We have developed methodologies to (1) allow for testing the significance of competition in natural communities, (2) determine the power of these estimates, and (3) produce maximum likelihood estimates of interaction parameters for these communities. Using these methodologies we show that small mammal communities at the interface between Valdivian temperate rain forest and Patagonian steppe in southern South America appear significantly and importantly structured by competition, although we cannot distinguish between resource competition, interference competition, and apparent competition. Secondarily, we show that the geographic origin of the component species (Valdivian vs. Patagonian) is relatively more important than their habitat affinities in structuring these communities.

A prolonged El Nino Southern Oscillation (ENSO) event during 1991–1992 with three times the normal annual 85-mm rainfall was accompanied by major changes in numbers of small mammals at a semiarid Mediterranean site in northcentral Chile. Several demographic patterns were evident. Akodon olivaceas , an omnivore, had a rapid increase in population size of more than an order of magnitude. Phyllotis darwini , a granivore-herbivore, showed somewhat delayed, smaller increases superimposed on annual oscillations. Octodon degus , an herbivore, showed a delayed response with larger increases and extended breeding in 1992–1993. Finally, Oligoryzomys longicaudatus , a granivore, experienced increases during both a dry (1990, ppt = 32 mm) and a wet year (1992). Other species such as Abrothrix longipilis, Abrocoma bennetti , and Thylamys elegans had smaller, delayed demographic responses. Reproductive rates for the first three species were higher due to the ENSO event only in O. degus males and P. darwini as a quadratic function of time. Survival rates of all four principal species were significantly greater during the 1991–1992 ENSO. Finally, average movement between captures was lower during ENSO years, suggesting behavioral changes. Explanations for these patterns include rainfall-related increases in food-resource levels ( A. olivaceus and P. darwini ), the importance of source-sink processes in vagile species from more mesic, adjacent habitats ( O. longicaudatus ), and delayed responses to extrinsic events in species with long gestation ( O. degus, A. bennetti ). The heterogeneity of species responses suggests different capabilities for small mammals to respond to an extrinsic, large-scale event, and it emphasizes the importance of long-term studies in semiarid systems.

South America spans about 44° latitude, covers almost 18 million km(2) , and is second only to Africa in continental mammal species richness. In spite of this richness, research on the status of this fauna and on the nature and magnitude of contemporary threats remains limited. Distilling threats to this diverse fauna at a continental scale is challenging, in part because of the limited availability of rigorous studies. Recognizing this constraint, we summarize key threats to small mammals in South America, emphasizing the roles of habitat loss and degradation, direct persecution, and the increasing threat of climate change. We focus on three regional 'case studies': the tropical Andes, Amazonia and adjacent lowland regions, and the southern temperate region. We close with a brief summary of recent findings at our long-term research site in north-central Chile as they pertain to projected threats to this fauna. Habitat alteration is a pervasive threat that has been magnified by market forces and globalization (e.g. extensive agricultural development in Amazonia), and threatens increasing numbers of populations and species. Climate change poses even greater threats, from changes in rainfall and runoff regimes and resulting changes in vegetative structure and composition to secondary influences on fire dynamics. It is likely that many changes have yet to be recognized, but existing threats suggest that the future may bring dramatic changes in the distribution of many mammal taxa, although it is not clear if key habitat elements (vegetation) will respond as rapidly as climatic factors, leading to substantial uncertainty. Climate change is likely to result in 'winners' and 'losers' but available information precludes detailed assessment of which species are likely to fall into which category. In the absence of long-term monitoring and applied research to characterize these threats more accurately, and to develop strategies to reduce their impacts, managers already are being faced with daunting challenges. As the line between 'pure' and 'applied' research blurs in the face of converging interests of scientists and society we hope that solutions to these critical issues will be incorporated in addressing anticipated conservation crises.

Multivariate analyses of distributions of small mammals identified important habitat associations in a precordilleran temperate rainforest in southern Chile. Significant differences in vegetation were found between summer (January–March) and winter (July–August) periods, indicating that multiple-season studies may be necessary to fully assess habitat preferences of small mammals. Three species of sigmodontines ( Akodon olivaceus, Abrothrix longipilis, Abrothrix sanborni ), and a putative A. longipilis × A. sanborni hybrid, showed moderate habitat preferences with considerable interspecific overlap. Habitat associations of Oligoryzomys longicaudatus , a sporadic resident, were significantly different from those of the akodonts, perhaps reflecting transient status in the community; other species generally had insufficient captures for quantitative comparisons. These patterns of habitat association differ from those of previous studies and suggest the consequences of methodological, spatiotemporal, and demographic factors in the interpretation and detection of multivariate ecological relationships.

Extreme climatic events represent disturbances that change the availability of resources. We studied their effects on annual plant assemblages in a semi-arid ecosystem in north-central Chile. We analysed 130 years of precipitation data using generalised extreme-value distribution to determine extreme events, and multivariate techniques to analyse 20 years of plant cover data of 34 native and 11 exotic species. Extreme drought resets the dynamics of the system and renders it susceptible to invasion. On the other hand, by favouring native annuals, moderately wet events change species composition and allow the community to be resilient to extreme drought. The probability of extreme drought has doubled over the last 50 years. Therefore, investigations on the interaction of climate change and biological invasions are relevant to determine the potential for future effects on the dynamics of semi-arid annual plant communities.

Desde 1989, hemos estudiado las poblaciones de micromamíferos en un sitio semiárido en el norte de Chile, mediante un complejo de grillas de trampeo-vivo a gran escala. La exclusión selectiva de depredadores vertebrados y/o posibles competidores micromamíferos ha resultado en efectos peque-ños y/o mayormente transitorios en la dinámica de micromamiferos y en la compositión de la comunidad de plantas. Durante el período de estudio, han habido 5 eventos lluviosos o El Niño con duratión de 1 a 3 años. Los micromamíferos residentes o centrales tales como Abrothrix olivaceus, Phyllotis darwini, y Octodon degus mostraron marcadas fluctuaciones durante y posteriormente a los pulsos de lluvias. Las especies oportunistas o de residencia transitoria tales como Oligoryzomys longicaudatus y A. longipilis desaparecen del ambiente de matorral espinoso por períodos variables de tiempo. Todas las especies persisten en ambientes cercanos más mésicos asociados a lechos de arroyos secos (aguadas). Después de 3 años lluviosos consecutivos entre el 2000 y 2002, el promedio anual de precipitaciones ha aumentado en esta región, principalmente debido a una ausencia de sequías prolongadas. Bajo estas condiciones y usando un modelo cualitativo propuesto por Noy-Meir, especies de larga vida pueden llegar a ser más abundantes. Los cambios del ensamble de micromamíferos son consistentes con estas predicciones, el roedor caviomorfo con una historia de vida larga, O. degus, ahora constituye una proporción más constante de la biomasa de micromamíferos del matorral espinoso, y ha habido una reductión en la variatión de la diversidad de especies. El aumento en las lluvias, que está pronosticado como una consecuencia del cambio climático global para esta región, puede estar causando cambios en la estructura y composición del ensamble de micromamíferos, y eventualmente resultará en un ensamble más estable y menos fluctuante en el matorral espinoso. A su vez, los grupos invasores como los lagomorfos y plantas efímeras introducidas pueden intensificar su establecimiento en esta comunidad. Por lo tanto, las consecuencias a largo plazo de los cambios en los patrones de lluvias debidos a El Niño Oscilación del Sur (ENOS) con importantes teleconexiones a fenómenos de escala global, causarán aquí cambios diversos al nivel de la comunidad. Since 1989 we have monitored small mammal populations at a semiarid site in north-central Chile with a large-scale livetrapping grid complex. Selective exclusions of vertebrate predators or putative small mammal competitors, or both, have yielded relatively small or mostly transitory effects, or both, on small mammal population dynamics and plant community composition. During the study period 5 El Niohigh rainfall episodes have occurred lasting 13 years. Resident or core small mammals such as Abrothrix olivaceus, Phyllotis darwini, and Octodon degus experience dramatic fluctuations during and following rainfall pulses. Temporary resident or opportunistic species such as Oligoryzomys longicaudatus and A. longipilis disappear from the thorn scrub for varying periods of time. All species persist in more mesic nearby habitats near dry stream courses (aguadas). Since a 3-year high rainfall event in 20002002 mean annual rainfall has increased in this region, mainly due to a lack of prolonged droughts. Under these conditions, and building on a qualitative model proposed by Noy-Meir, long-lived species might become more abundant. Changes in the small mammal assemblage are consistent with these predictions; O. degus, a caviomorph rodent with a long life span, now comprises a more constant proportion of the small mammal biomass in the thorn scrub, and we have documented reduced variation in species diversity. Increased rainfall, a predicted consequence of global climate change in this region, might be leading to changes in small mammal assemblage structure and composition and ultimately will result in a more stable, less oscillatory assemblage in the thorn scrub. Additionally, invasive groups such as introduced lagomorphs and ephemeral plants might become more abundant in this community. The long-term consequences of changes in rainfall patterns due to El Nio Southern Oscillations (ENSOs), with important teleconnections to global-scale phenomena, will lead to diverse changes at the community level here. Fil: Meserve, Peter L.. University of Illinois; Estados Unidos Fil: Kelt, Douglas A.. University of California; Estados Unidos Fil: Previtali, Maria Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Cary Institute of Ecosystem Studies; Estados Unidos Fil: Milstead, W. Bryan. United States Environmental Protection Agency; Estados Unidos Fil: Gutiérrez, Julio R.. Universidad de La Serena; Chile

Foresman, K. R. 2012. Mammals of Montana. Montana Press Publishing Company, Missoula, Montana, 430 pp. ISBN 978-0-87842-590-7, price (paper), $32.

The effects of vertebrate predation have been monitored since 1989 on 16 replicated 0.56 ha study plots in a semiarid thorn scrub community in north-central Chile. Using fences of different heights with and without holes and suspended game netting to alter principal predator (foxes and raptors) and large rodent herbivore (Octodon degus) access, four grids each have been assigned to the following treatments: 1) low fencing and holes allowing free access of predators and small mammals; 2) low fencing without holes to exclude degus only; 3) high fencing and netting with holes to exclude predators only; and 4) high fencing and netting without holes to exclude predators and degus. Small mammal population censuses are conducted monthly using mark-recapture techniques. Degu population trends during 1989 and 1990 showed strongly but nonsignificantly lower numbers in control plots during months when densities were characteristically low (September-November) for this seasonally reproductive species; since March 1991, differences have become persistent and increasingly significant. Predators appear to have greater numerical effects when their prey populations are low. Survival times of degus, particularly established adults, were significantly longer in predator exclusion grids during the 2 1/2 years of observation; thus, predation also affects prey population structure.

Increase in rainfall variability has important consequences for organisms in arid and semiarid regions around the world. In South American and Australian deserts, the El Nino/Southern Oscillation (ENSO) phenomenon greatly influences rainfall patterns, and therefore the dynamics of plant communities. However, the field data needed to assess the effect of climate change on vegetational patterns is difficult to obtain because of the large spatial scale required for such studies. Normalized Difference Vegetation Index (NDVI) characteristics allow the use of several indexes related to vegetational structure. Due to its direct relationship with primary productivity, it is possible to obtain several measures of annual productivity. These include annual plant yield, annual maximum yield, onset of 'greening-up' and senescence phases, length of the 'green' season, vegetation peak, and therefore, the periods when more or less food is available for herbivores. After verification with ground-truth measures, we used NDVI data from two semiarid localities in north-central Chile (Fray Jorge and Auco ´ ) to determine the relation- ship between rainfall patterns and vegetation cover and productivity related to El Nino phenomenon. With this information we gauge the influence of climatic processes on primary productivity in western South America, an area subject to strong climate variability. We predict significant variation in Chilean semiarid regions due to climate change, affecting mainly the extent and timing of annual growth season of vegetation, and also including a shorter and delayed greening-up season. Also, we predict that important decreases in rainfall levels will not have strong effects on primary production in these semiarid ecosystems.

Precipitation plays an important role in the dynamics of species found in arid and semiarid environments. However, population fluctuations generally are driven by a combination of multiple factors whose relative contribution may vary through time and among species. We monitored fluctuations of species in three trophic levels for >17 years at a semiarid community in north-central Chile. The region is strongly affected by the El Nino Southern Oscillation, resulting in high variation in rainfall that triggers dramatic changes in food resource availability, with strong effects on upper trophic levels. We focused our analyses on the role played by endogenous and exogenous (climatic) factors on the dynamics of two important rodent species in the community, Octodon degus and Phyllotis darwini. We documented population fluctuations of several orders of magnitude in response to wet and dry episodes of different strength and duration. P. darwini reached similar maximum densities, regardless of the duration of high-rainfall events, whereas O. degus showed additive effects of multiple wet years. Time series diagnostic tools revealed oscillations with a 5-year periodicity in rainfall, which may be the cause of the same periodicity and a weak second-order signal observed in the rodent dynamics. However, the dynamics of both rodent species were dominated by strong first-order processes, suggesting an important role of direct density dependence. Intraspecific competition, expressed as the ratio of rodent density/rainfall (or food resources) explained more than two-thirds of the variation in the population rate of change, whereas less than one-third was explained by lagged rainfall (or food resources). We detected no significant effects of predation. Our results contribute to a growing number of examples of dynamics governed by the combined effect of density dependence and climatic forcing. They also reveal strong bottom-up regulation that may be common in other arid environments.

Distribution and abundance of small mammals in temperate Andean rainforests are correlated with elevation. To interpret such patterns, we examined elevational variation in habitats and habitat use by small mammals. Elevation accounts for significant variation in 22 of 24 habitat metrics, reflecting the diminishing stature and more open canopies of higher-elevation rainforests. Principal-components analysis of habitat shows significant multivariate effects of elevation. Mammal species differ significantly in use of about half of the habitat variables, in ways generally consistent with morphology, behavior, and diet. Abundant species appear to occupy typical habitats along the transect, whereas rarer species are associated with more distinctive habitat types. Species overlap substantially in their use of habitats, but analyses of trap captures indicate that species are segregated at finer spatial scales. Spatial segregation at this scale may contribute to the coexistence of abundant species and congeners. Elevational variation in habitat and specific habitat associations provide a plausible explanation for correlations of mammalian distribution and abundance with elevation.

South America forms the greater part of the Neotropical faunal realm, which extends northward through Central America to tropical southern Mexico. Although making up only 12% of the world’s land area, South America is the richest continent for virtually all organismal groups, including vertebrates. For example, of the known 23,250 species of fish (Eschmeyer, 1998), 41% or 9,530 species are freshwater, and of these, more than 2,800 species (29%) are in South America (Moyle and Cech, 2000). A comparable level of diversity exists for amphibians and birds. Of Earth’s 5,900 species of amphibians, at least 1,749 or 30% occur in South America (Duellman, 1999a, 1999b; Köhler et al., 2005; www.amphibiaweb.org). More than 3,200 (or nearly 32%) of Earth’s 9,900 species of birds occur in South America (Sibley and Monroe, 1990). For reptiles and mammals, diversity is only slightly lower; at least 1,560 (19%) of 8,240 reptile species (Uetz and Etzold, 1996; www.reptiledatabase. org), and 1,037 (19%) of 5,416 mammal species (Nowak, 1999; Wilson and Reeder, 2005) are found in South America. Four major geological events or features are important to understanding South America’s contemporary zoogeography. The first was the breakup of Pangea, and then of Gondwana. South America and Africa remained close for an extended period of the Mesozoic, and thus share important similarities in their faunas, including groups not fully evolved at the time of separation. South America also maintained connections to other Gondwanan continents, directly with Antarctica, indirectly with Australia, until the early Cenozoic. The second major feature was South America’s long period of isolation in the Cenozoic, particularly from North America pending establishment of the late Pliocene land bridge after 3 Ma (million years before present). The latter resulted in “The Great American Interchange” (Webb, 1976; Marshall et al., 1982), which had profound consequences for the fauna. The third major feature of South America has been the Andes, which, in addition to modifying climate, have been a center of speciation, a dispersal route, and a barrier. The cordillera has had an overriding effect on distributions and histories of both past and current biotas on the continent.

6 Climatic changes associated with the El Nino Southern Oscillation (ENSO) can have a dramatic impact on ter- restrial ecosystems worldwide, but especially on arid and semiarid systems, where productivity is strongly lim- ited by precipitation. Nearly two decades of research, including both short-term experiments and long-term studies conducted on three continents, reveal that the initial, extraordinary increases in primary productivity percolate up through entire food webs, attenuating the relative importance of top-down control by predators, providing key resources that are stored to fuel future production, and altering disturbance regimes for months or years after ENSO conditions have passed. Moreover, the ecological changes associated with ENSO events have important implications for agroecosystems, ecosystem restoration, wildlife conservation, and the spread of disease. Here we present the main ideas and results of a recent symposium on the effects of ENSO in dry ecosystems, which was convened as part of the First Alexander von Humboldt International Conference on the El Nino Phenomenon and its Global Impact (Guayaquil, Ecuador, 16-20 May 2005).