Mammal Community Structure Research Articles

Gastrointestinal morphology is an effective functional dietary proxy that predicts small mammal community structure.

The availability and quality of food resources can alter the intensity of competition and predation pressure within communities. Understanding species capacity to respond to global change-driven shifts in resource distribution is therefore crucial for biodiversity conservation. Small mammal communities are often structured by competition for food resources, but understanding and monitoring these processes are currently hindered by lack of functional dietary trait information in these hard-to-sample systems. In this study, we collected a comprehensive suite of gastrointestinal (GI) measurements from 26 small mammal species (including some never reported), compared them with more traditional craniodental traits in predicting dietary guild, and used them in a novel way to understand how diet structures 22 small mammal communities across the Appalachian Mountains of eastern North America. As predicted, we found GI traits to be effective dietary trait proxies; they were equally or more accurate than craniodental proportions in predicting the dietary guild of individual species. Furthermore, at the community level, we found that both the mean and functional dispersion of GI length were positively correlated with latitude and measures of temperature seasonality. Our results indicate that small mammal communities in more seasonal environments are filtered to include species with longer GI tracts (on average) as well as those that can partition food resources more finely, as expected based on the lower productivity of these regions. Conversely, communities in less seasonal environments display functional redundancy from the addition of species with short to intermediate GI lengths. Proportions of the GI tract represent novel dietary traits that can illuminate community assembly processes across regional environmental gradients and in the face of changing timing and availability of resources.

Small mammal diversity and community structure exhibit congruent hump-shaped patterns along a subtropical elevational gradient

Incomplete elevational sampling in studies of biodiversity and community assembly along elevational gradients can result in inconsistent findings and potentially inaccurate conclusions about assembly mechanisms. In this study, we conducted extensive sampling of small mammals over a 3200 m elevational gradient on Xiling Snow Mountain, Southwestern China. We integrated functional and phylogenetic diversity to determine the mechanisms structuring small mammal assemblages. Our findings indicate that taxonomic, functional, and phylogenetic diversity, along with all species richness-corrected indices of functional and phylogenetic diversity, exhibit similar hump-shaped patterns. Our results suggest that environmental filtering plays a considerable role in structuring small mammal communities at low and high elevations, while competitive exclusion governs the assembly processes at middle elevations. Human footprint, Normalized Difference Vegetation Index, precipitation seasonality and potential evapotranspiration are key drivers of small mammal diversity and community structure along elevational gradients. In summary, our study provides evidence that phylogenetic diversity is a robust surrogate for functional diversity, and challenges the recent large-scale studies that advocate a linear relationship between small mammal assembly process and elevation. We emphasize the importance of continuously documenting general patterns of small mammal diversity across entire elevational gradients in future studies.

The nature of vegetation cover and small mammal community structure (on the example of Nizhny Novgorod)

The spatial distribution of Apodemus species (yellow-necked, field, and small forest mice) was studied on the example of the protected area «Oak forest of National Research Lobachevsky State University of Nizhny Novgorod Botanical Garden». Twelve plant associations with non-moral character and representing derivatives of the indigenous type of vegetation were studied. Environmental conditions assessed by the Ellenberg phytoindication method affect the distribution of small mammals in space indirectly. The nature of vegetation cover is more significant. When projective cover increases, the abundance of both small woodland and field mice increases. The strategy of Apodemus agrarius appears to be similar to that of Apodemus uralensis, a species that shows stenobiontic traits in the studied PA. At the same time, insignificant anthropogenic load, a marker of which is the presence of Urtica dioica ruderal species, leads to an increase in the mosaic of vegetation cover, which has a positive effect on the abundance of these small mammal species. A moderate increase in the Berger-Parker dominance index for vegetation cover is positively associated with the confinement of micromammals. In addition, in the conditions of the recreational zone of the upland part of N. Novgorod, Apodemus agrarius prefers areas of old-growth broadleaved forest, not showing the features of anthropophily.

Unique functional diversity during early Cenozoic mammal radiation of North America.

Mammals influence nearly all aspects of energy flow and habitat structure in modern terrestrial ecosystems. However, anthropogenic effects have probably altered mammalian community structure, raising the question of how past perturbations have done so. We used functional diversity (FD) to describe how the structure of North American mammal palaeocommunities changed over the past 66 Ma, an interval spanning the radiation following the K/Pg and several subsequent environmental disruptions including the Palaeocene-Eocene Thermal Maximum (PETM), the expansion of grassland, and the onset of Pleistocene glaciation. For 264 fossil communities, we examined three aspects of ecological function: functional evenness, functional richness and functional divergence. We found that shifts in FD were associated with major ecological and environmental transitions. All three measures of FD increased immediately following the extinction of the non-avian dinosaurs, suggesting that high degrees of ecological disturbance can lead to synchronous responses both locally and continentally. Otherwise, the components of FD were decoupled and responded differently to environmental changes over the last ~56 Myr.

Small mammal assemblages in heterogeneous landscapes at the Southern tip of Italian peninsula evidence clear eco-biogeographic patterns

We investigated the frequencies of sympatric small mammal species in 12 habitat-types located in the extreme south of the Italian peninsula (Calabria) using trapping techniques. Ten species were detected with Apodemus sylvaticus, the most abundant species. The assemblages of small mammal species recorded in the 12 selected habitat types revealed clear ecological and biogeographical patterns in the extreme southern tip of the Italian peninsula. Ecologically, we observed a clear dissimilarity between a guild of species linked to thermo-xerophilous habitat types and a comparable guild of mesophilous species linked to forest and sciaphilous habitat types. The differences among communities inhabiting in different habitat types also emerged in rarefaction curves, DCA analysis and Whittaker plots. Thus, all these sets of analyses were consistent in their interpretation of the variation of small mammal community structure along the gradient (β-diversity) among habitat types. From a biogeographical point of view, this is an apparent expression of a clear North–South gradient pattern that was already observed at the species level with Calabria being characterized by a strong impoverishment in species’ richness and diversity (“peninsula effect”). However, this rationale has been based so far on indirect data of small mammals preyed upon and recorded in owl’s pellets: the fact that a similar pattern was obtained also using small mammals recorded by traps indicates that the results were robust and generalizable. Ecological factors at the local scale and biogeographical factors at the peninsular scale could explain the community patterns that we observed in the present study.

On the Dynamics of Mortality and the Ephemeral Nature of Mammalian Megafauna.

AbstractEnergy flow through consumer-resource interactions is largely determined by body size. Allometric relationships govern the dynamics of populations by impacting rates of reproduction as well as alternative sources of mortality, which have differential impacts on smaller to larger organisms. Here we derive and investigate the timescales associated with four alternative sources of mortality for terrestrial mammals: mortality from starvation, mortality associated with aging, mortality from consumption by predators, and mortality introduced by anthropogenic subsidized harvest. The incorporation of these allometric relationships into a minimal consumer-resource model illuminates central constraints that may contribute to the structure of mammalian communities. Our framework reveals that while starvation largely impacts smaller-bodied species, the allometry of senescence is expected to be more difficult to observe. In contrast, external predation and subsidized harvest have greater impacts on the populations of larger-bodied species. Moreover, the inclusion of predation mortality reveals mass thresholds for mammalian herbivores, where dynamic instabilities may limit the feasibility of megafaunal populations. We show how these thresholds vary with alternative predator-prey mass relationships, which are not well understood within terrestrial systems. Finally, we use our framework to predict the harvest pressure required to induce mass-specific extinctions, which closely align with previous estimates of anthropogenic megafaunal exploitation in both paleontological and historical contexts. Together our results underscore the tenuous nature of megafaunal populations and how different sources of mortality may contribute to their ephemeral nature over evolutionary time.

Contribution of community monitoring to knowledge of mammal diversity in voluntarily conservation areas in Southern Mexico

In southern Mexico, Voluntarily Designated Conservation Areas (VCA) represent a biological conservation strategy wherein governance and management are entrusted to the territory. Within the VCAs of the La Chinantla region in the state of Oaxaca, Mexico, community monitoring utilizing camera traps has been conducted with the assistance of government programs. This initiative has yielded a substantial number of records for medium and large mammals. Nevertheless, the available information has not undergone systematic analysis, constraining its utility in strategic planning and the evaluation of biodiversity conservation endeavors. This study seeks to highlight the impact of community monitoring in 18 VCAs on understanding the altitudinal distribution of mammal diversity in La Chinantla. The analysis incorporates data from a community monitoring covering 129 camera trap stations (4,384 camera days) strategically positioned along an elevation gradient ranging from 50 to 2000 m above sea level, over the period 2011–2014. We assessed alpha and beta diversity, as well as the community structure of medium and large mammals within three distinct elevation zones. A total of 26 species of medium-sized mammals were documented, revealing distinct mammal assemblages in each zone. However, 15 species were common across all zones. We found that the highest species richness was observed below 400 m, where tropical rainforest vegetation predominates. We also found that the species turnover component had a significant impact on the total beta value. Despite the considerable involvement of local residents in the monitoring program and their acquisition of social, technical, and ecological knowledge, there is still a need to strengthen their capabilities to enhance community monitoring. Finally, fostering collaboration between local communities, academic institutions, and governmental initiatives is essential for the successful conservation of mammals in La Chinanlta.

Projecting community trophic structures for the last 120 000 years

Studying past community dynamics can provide valuable insights for anticipating future changes in the world's biota. However, the existing fossil record is too sparse to enable continuous temporal reconstructions of wholesale community dynamics. In this study, we utilise machine learning to reconstruct Late Quaternary community structure, leveraging the climate–trophic structure relationship. We followed a four‐stage approach: 1) identify and map trophic structure units (TSUs) at the global scale based on the guild richness and composition of terrestrial mammal species weighing over 3 kg; 2) train a random forest classifier to predict the observed distribution of TSUs based on contemporary climatic conditions; 3) hindcast the global distribution of TSUs using climatic conditions as reconstructed over the past 120 000 years; and 4) compare TSU hindcasts against elements of community structure as estimated with the fossil record. Models project significant shifts in the geographical distribution of community trophic structures, with more pronounced changes occurring during the Pleistocene–Holocene transition. These shifts exhibit regional variations, particularly in Eurasia and North America, where the models project reductions in the distribution of less‐complex trophic structures over the last 24 000 years. Hindcasts partially identified the alterations in community structure seen in the fossil record, demonstrating a match between the observed and predicted times of change in mammal community structure (between 24 and 8 ka BP). However, projections of trophic guilds diverged from fossil records during the Holocene. While the fossil record indicated a decrease in the number of grazers and carnivores, our models projected an increase in these numbers. Characterising community‐wide responses to climatic changes is essential to address key questions about past and future impacts of such changes. Although further research is needed to refine the models, our approach offers a perspective for addressing the complex interactions among climate and trophic structures and model their distributions over time.

Seasonal acoustic presence of marine mammals at the South Orkney Islands, Scotia Sea.

Increased knowledge about marine mammal seasonal distribution and species assemblage from the South Orkney Islands waters is needed for the development of management regulations of the commercial fishery for Antarctic krill (Euphausia superba) in this region. Passive acoustic monitoring (PAM) data were collected during the autumn and winter seasons in two consecutive years (2016, 2017), which represented highly contrasting environmental conditions due to the 2016 El Niño event. We explored differences in seasonal patterns in marine mammal acoustic presence between the two years in context of environmental cues and climate variability. Acoustic signals from five baleen whale species, two pinniped species and odontocete species were detected and separated into guilds. Although species diversity remained stable over time, the ice-avoiding and ice-affiliated species dominated before and after the onset of winter, respectively, and thus demonstrating a shift in guild composition related to season. Herein, we provide novel information about local marine mammal species diversity, community structure and residency times in a krill hotspot. Our study also demonstrates the utility of PAM data and its usefulness in providing new insights into the marine mammal habitat use and responses to environmental conditions, which are essential knowledge for the future development of a sustainable fishery management in a changing ecosystem.

The Diversity of Small Mammals along a Large River Valley Revealed from Pellets of Tawny Owl Strix aluco.

The Vistula River is one of the largest European semi-natural rivers of high ecological value that functions as an ecological corridor. To assess the structure of small mammal communities along the Vistula River, an analysis of the diet of an opportunistic predator, the tawny owl Strix aluco, was used. A total of 6355 individuals of 19 species were found, including 5 soricomorph species, 12 rodents, 1 carnivore, and 1 bat species. Tawny owls most frequently caught Apodemus agrarius, Clethrionomys glareolus, Apodemus flavicollis, and Microtus arvalis. Rodents dominated small mammal communities (90%), followed by soricomorphs (8%), and the share of Chiroptera was significant (2%). Using Ward's method in cluster analysis, three clusters of sites with similar mammal communities were identified. The cluster that included 17 study sites with the dominance of agriculture habitats was inhabited by diverse mammal communities with a high number of species. In the cluster composed of three suburban forest sites, mammal communities had the lowest diversity, although the high species richness and the highest shares of the forest species (A. flavicollis, C. glareolus, and Nyctalus noctula). Mammal communities in the cluster were composed of three urban sites were dominated by A. agrarius and M. arvalis. The study indicates the high species richness of small mammals in floodplains of the Vistula River and the adjacent areas in central Poland. The floodplain offers suitable habitats for species associated with forests, water bodies, agricultural land, and developed areas. The data collected confirms earlier model predictions about the presence of well-connected local populations of forest mammals along the Vistula River.

Estimating the effects of land abandonment on mammal communities in the Karoo region of South Africa

Small livestock production has significantly transformed natural land within South Africa, but the extent and nature of the impacts of this land use on wildlife remains poorly understood. The establishment of a formal protected area (PA) within a well-established small livestock farming area in the Karoo provided a unique opportunity to investigate the response of mammal communities to both sustained farming impacts and how the cessation of farming activities across a large area may impact the persistence and colonisation of highly mobile species. Through extensive camera trapping and a dynamic multi-species occurrence model within a (Before-After-Control-Intervention) BACI design, we investigated the community diversity and structure of medium and large mammals in addition to changes in their persistence and colonisation following this land use change. Camera traps detected 25 species, from 14 families, within the combined study area. Community-level and species-specific probability of colonisation and persistence did not differ significantly between land that remained in use for commercial livestock farming and that which was abandoned to form a new protected area. Farmer concerns that predators would leave the PA and colonise their farms were not supported. Long term monitoring of these sites will prove important to our understanding of the potential of land, subject to prolonged livestock farming, to recover and support higher levels of species richness and wildlife abundance.

Peculiarities of the Dynamics and Structure of Small Mammal Communities at High Latitudes

Peculiarities of the Dynamics and Structure of Small Mammal Communities at High Latitudes

Low impact of forest conversion on biodiversity: Evidence from small mammals in contrasting forests of Mt. Liangshan

AbstractSecondary and plantation forests are the main alternative forests remaining after the deforestation of primary forests. Understanding the conservation value of secondary and plantation forests is important for biological conservation. To explore the impact of forest conversion on biodiversity, we compared multiple diversity metrics (taxonomic, phylogenetic, and functional diversity) and community structure of small mammals in the primary, secondary, and plantation forests in Mt. Liangshan, Sichuan Province, China. Three field surveys were conducted in each of the three forest types to characterize local small mammal assemblages from 2017 to 2020. We found that the taxonomic, phylogenetic, and functional diversity of small mammals in the three forest types were similar at the landscape scale, while all diversity metrics were lowest in the plantation forest and highest in the primary forests at the site scale. The community structure analysis showed that habitat filtering was the dominant process driving the assembly of small mammal communities across the three forest types, and there was no statistically significant difference in small mammal community structure among the three forest types. Our results indicated that secondary and plantation forests in the nature reserves, adjacent to the primary forest and exposed to little human disturbance, also can provide important habitats for small mammals.

Implications of Immigrant Arrival Times During the Paleocene-Eocene Thermal Maximum for Mammal Biogeographic Response to Modern Climate Change

Abilities of taxa to track suitable habitat under climate change is a concern in conservation biology. Projections that assume suitable habitat is limited to currently occupied biomes can produce underestimates of species viability. The geological record is a valuable source of data to test assumptions about habitat tracking because it archives past episodes of climate change. The Paleocene-Eocene Thermal Maximum (PETM) ~56 million years ago was an interval of rapid carbon release (millennial scale) and global warming (~5 C) that caused large geographic range shifts in Earth’s biota. Large, stratigraphically controlled fossil collections spanning the PETM in the Bighorn Basin, Wyoming, document first occurrence data for immigrant mammals and plants, providing evidence of geographic range shifts as well as changes in climate, flora and vegetation. If mammals tracked specific habitats, their intercontinental dispersal would imply continuity of biomes across Holarctica. In that case, intercontinental mammal and plant immigrants should appear concurrently. Instead, mammalian immigrants crossed high latitude belts of warm, temperate forest, then appeared in the Bighorn Basin during the warmest part of the PETM when plant fossils suggest a dry tropical forest. Warm temperate Eurasian plants are rare during the body of the PETM, but become abundant during the recovery, as climate became wetter. Floral change during the PETM recovery is not concurrent with change in mammalian community structure. Distinct patterns of mammalian and plant turnover suggest that mammals did not strictly track plant-defined habitats. Species may be capable of more flexible responses to rapid climate change than current models predict. Efforts that support movement and provide multi-latitudinal networks of protected areas should be prioritized as a viable means to help conserve some species in the face of climate change.

Pliocene Pre-GABI herbivorous mammals from Espinar, Peruvian Andean Plateau

ABSTRACT Pliocene South American mammals prior to the Great American Biotic Interchange comprise the evolutionary pinnacle of a long-lasting process of continental isolation, in which large-scale orogeny and climate change were instrumental. These processes resulted in unique assemblages of extinct groups with peculiar anatomies. However, interpretation of the functional roles that these organisms would have played in the ecosystem is challenging because well-preserved fossils of this time interval in South America are scarce. Here, we describe a new Early Pliocene assemblage of native herbivorous megamammals documented by skeletons in anatomical connection from the Peruvian Andean plateau (city of Yauri in Espinar, Cusco Department). Fossil-bearing deposits pertain to Member C of the El Descanso Formation dated at 4.75 ± 0.5 Ma, when the plateau attained near-modern elevations and a Puna-type plant ecosystem. The mammal assemblage is dominated by xenarthrans, including three ground sloths (cf. Megatheriops rectidens, Simomylodon uccasamamensis, and Proscelidodon sp.) and Andinoglyptodon mollohuancai gen. et sp. nov., the first Pliocene glyptodontine known by a well-preserved cranium and dermal armor. Notoungulates are represented by the toxodontid Posnanskytherium viscachanense. Both selective and bulk feeders are identified, suggesting the existence of diverse plant resources in the Pliocene Puna ecosystem. These native mammals constituted the typical Pliocene herbivorous guild of the central Andean plateau and provide an opportunity to investigate the structure of mammalian communities just before the arrival of Holarctic immigrants.

Impact of habitat variation and human activities on small mammal community structure and diversity in Diannan Town, Jianchuan County, Yunnan

Impact of habitat variation and human activities on small mammal community structure and diversity in Diannan Town, Jianchuan County, Yunnan

Logged tropical forests have amplified and diverse ecosystem energetics

Old-growth tropical forests are widely recognized as being immensely important for their biodiversity and high biomass1. Conversely, logged tropical forests are usually characterized as degraded ecosystems2. However, whether logging results in a degradation in ecosystem functions is less clear: shifts in the strength and resilience of key ecosystem processes in large suites of species have rarely been assessed in an ecologically integrated and quantitative framework. Here we adopt an ecosystem energetics lens to gain new insight into the impacts of tropical forest disturbance on a key integrative aspect of ecological function: food pathways and community structure of birds and mammals. We focus on a gradient spanning old-growth and logged forests and oil palm plantations in Borneo. In logged forest there is a 2.5-fold increase in total resource consumption by both birds and mammals compared to that in old-growth forests, probably driven by greater resource accessibility and vegetation palatability. Most principal energetic pathways maintain high species diversity and redundancy, implying maintained resilience. Conversion of logged forest into oil palm plantation results in the collapse of most energetic pathways. Far from being degraded ecosystems, even heavily logged forests can be vibrant and diverse ecosystems with enhanced levels of ecological function.

Community structure of medium-large mammals across a tree plantation cycle in natural grasslands of Uruguay

In temperate South America, the conversion of natural grasslands into crops and exotic tree plantations, such as with Eucalyptus sp., has reached outstanding levels, especially in the Río de la Plata Grasslands. The cycle of Eucalyptus plantations for pulp production is a very dynamic phenomenon; however, most of the studies on the impacts on biodiversity have been static and focused on the mature stage of the plantation. We studied the mammal assemblage in a grassland afforestation landscape of Uruguay to address how mammals respond to habitat complexity variation across the plantation cycle and landscape characteristics. We installed 26 camera traps for two years in four different age stages of Eucalyptus plantations and native habitats to assess mammals’ richness, composition, and intensity of habitat use. We registered 16 mammal species, 13 native and three exotics, with a sampling effort of 19,136 camera-nights. Of these species, 11 were found in the Eucalyptus plantations but with significant variability during the production cycle. Only one species was recorded at the beginning (0–2 years) of the cycle and four species at the end (8–10 years). But at intermediate ages (2–4 years), when vegetation complexity resembles a native forest structure, species richness was maximum (11 species) in the plantations and relatively close to forest richness (14 species). Species composition was also determined by habitat structure, but it was further modulated by landscape features, particularly the proximity to native forests and landscape heterogeneity. Our results demonstrated that asynchronous plantations promote spatial heterogeneity that favors mammal diversity in afforested landscapes, but for grassland mammals, additional conservation management measures are needed.

Effects of intensive agricultural landscapes on farmland use by medium and large mammals in Japan

ABSTRACT This study aimed to determine the effects of landscape differences associated with intensive agricultural activities on farmland use by medium and large mammals in Japan. We compared the species diversity of mammals that used farmland within three regions with different agricultural activity levels, and analyzed the relationship between the occurrences and escape responses of mammals in the farmland and surrounding landscape. We used spotlight count in intensive (high agricultural activity), intermediate (moderate agricultural activity), and non-intensive (low agricultural activity) areas. We observed 271 and 199 occurrences of mammals in spring and autumn 2021, respectively. Seasonal changes in mammals occurrence were due to a decrease in the number of raccoon dogs observed. Species richness tended to be lower in intensive agricultural areas than in other areas, suggesting that intensive agricultural landscapes negatively affect the community structure of medium and large mammals. Generalized additive models showed that the effects of the surrounding landscape on the occurrences and escape responses of raccoon dogs, red foxes, and cats differed among species. Only raccoon dogs were negatively affected by the surrounding farmland, suggesting high sensitivity to agricultural activities. Our results have important implications for the management of ecosystems in Japanese agricultural areas.

Small Mammal Diversity Changes in a Baltic Country, 1975-2021: A Review.

The structure and diversity of small mammal (SM) communities over the long term may show the influences of climate change, landscape changes and local disturbances. We review published data regarding SM trapping and owl pellet analysis from Lithuania (the most southerly of the three Baltic States, Northern Europe), covering the period 1975-2021. Over decades, we analysed trends in the diversity of SM communities and the proportions of species and proportions of trophic groups. The large increase in granivores, from 6.9% in 1975-1980 to 45.4% in 2011-2020 and 54.7% in 2021, coincided with a decrease in omnivores and insectivores. The proportion of herbivores increased less notably. At the species level, significant decreases in the proportions of M. arvalis, C. glareolus and S. araneus were accompanied by notable increases in the proportions of A. flavicollis and A. agrarius, the latter from 1.0% in 1975-1980 to 25.3% in 2021. Concluding, two periods were identified, specifically before the 1990s and subsequently. In the second period, in the aftermath of land-use changes within the country in 1990, diversity increased, and dominance decreased, a situation that has not subsequently changed. Not excluding the concomitant effects of climate change, we relate these patterns to the alterations in habitat and anthropogenic impact.