Response Of Small Mammal Communities Research Articles

The response of small mammal communities to low and high fire recurrences in Kafue National Park, Zambia

The response of small mammal communities to low and high fire recurrences in Kafue National Park, Zambia

Responses of small mammal communities to environment and agriculture in a rural mosaic landscape

Intensification of agriculture is an increasing threat for biodiversity. Central Romania still preserves a traditional rural landscape with a matrix of small plots of crops and large surfaces covered by grasslands and forests, but its biodiversity is very poorly studied. Small mammals are key components of agrarian and semi-natural ecosystems but rodents are also viewed as major pests. Knowledge of the driving factors of small mammal communities in agricultural landscapes may enable taking management measures that pursue both conservation and economic goals. Here we evaluate the response of small mammals to environmental variables, including vegetation characteristics, land use and geographic position. We conducted live trapping between June and October in habitats with different environmental characteristics and land uses. We found that vegetation traits were the most important factors influencing small mammal communities. Species composition was shaped mainly by tree cover, shrub cover had strong effects on community diversity and abundance, while the height of the herbaceous layer significantly influenced all the parameters. Among the agrarian land uses maize crops stood out for the abundance of mice, especially Mus musculus, and hayfields for Microtus arvalis. Land fallowing was linked to the increase of diversity and total abundance to the maximum values but did not significantly alter species composition. Species with low tolerance to tree cover were more prone to be abundant in agricultural lands, whereas the habitat generalists prevailed in non-agrarian lands. Our results suggest that preservation of the mosaic of farmed and semi-natural habitats and actions targeted for vegetation management, such as interspersing woody vegetation in the crop matrix and mowing the herbaceous vegetation in semi-natural habitats adjacent to crops, may together achieve the balance between biodiversity conservation and crop protection.

Responses of Small Mammal Communities to Pinyon-Juniper Habitat Treatments

Small mammals should be considered in wildlife management decisions because they are an important component of ecosystems. We examined small mammal population abundances (N) on 4 habitat treatment types in Colorado pinyon pine (Pinus edulis)—Utah juniper (Juniperus osteosperma) woodlands on the Uncompahgre Plateau, Montrose, Colorado. We trapped small mammals in Sherman live traps on 4 habitat treatment types—including 2 types of management treatments (chaining, roller chop), sites with high drought-related mortality of pinyon pine, and sites of mature pinyon-juniper (PJ) woodland—on 3 mesas. We modeled detection probability of deer mice (Peromyscus maniculatus) and least chipmunks (Tamias minimus) as a function of 4 treatment types on 3 mesas during 2 trapping periods by using Huggins closed mark-recapture models. A variance components analysis was conducted to obtain abundance shrinkage estimates and to separate spatial process variance from the sampling variance to calculate the percent of variation in abundance estimates explained by treatment type, mesa, and trapping period. Abundance estimates were higher for deer mice and least chipmunks on chaining and roller chop treatment sites than on mature PJ woodland and pinyon pine natural mortality sites. The highest percent of variation in abundance estimates was explained by treatment type for deer mice (33.67%) and least chipmunks (61.45%) and secondarily by mesa for deer mice (21.64%). We calculated species diversity using Shannon's, Simpson's, Pielou's evenness, and species richness indices, and we used analysis of variance to test for significant differences (P < 0.05) in species composition. Species diversity and richness were higher on natural mortality sites than on chaining, roller chop, and mature woodland sites. Our results indicate that chaining and roller chop habitat treatments within PJ woodlands have a positive impact on deer mouse and least chipmunk abundances, whereas natural mortality and chaining treatments have a positive impact on small mammal composition.

Biotic and Abiotic Forcing During the Transition to Modern Grassland Ecosystems: Evolutionary and Ecological Responses of Small Mammal Communities Over the Last 5 Million Years

Understanding the origin of modern communities is a fundamental goal of ecology, but reconstructing communities with durations of 103–106 years requires data from the fossil record. Early Pliocene to latest Pleistocene faunas and sediments in the Meade Basin and modern soils and rodents from the same area are used to examine the role of environmental change in the emergence of the modern community. Paleoenvironmental proxies measured on modern surface soils and paleosols are described, and faunal dynamics of fossil rodents are discussed. Mean annual precipitation (MAP) was estimated from elemental concentrations and magnetic properties, and warm-season temperature and δ18O of soil water was estimated using carbonate isotope paleothermometry on pedogenic nodules. MAP and temperature estimates from paleosols exhibit no short-term variability, no long-term trends, and generally bracket modern values. Estimated soil water δ18O values increased through time, suggesting aridification played a role in the evolution of the regional grassland ecosystem. Carbon isotope analyses of biomarkers are used to examine the abundance of C4 grasses, which suggest more C4 biomass and more variability in C4 biomass than carbonate proxies. Rodent species richness remained constant due to balanced rates of extinction and immigration, both of which show episodic spikes consistent with a balance between forcing mechanisms that result in equilibrium on long time scales. Overall, these results suggest that different mechanisms of faunal change may be acting at different time scales, although the stratigraphic resolution of paleoenvironmental proxies needs to be increased, and body size and dietary distributions of rodents need to be determined before which processes of change are most important can be decided.

Terminal Pleistocene change in mammal communities in southeastern Washington State, USA

Small mammal communities in western North America experienced declines in taxonomic richness across the late Pleistocene to Holocene transition (PHT), a recent natural global warming event. One community also experienced a decline in evenness and others replaced one species with a congener. Variability in response of small mammal communities to PHT warming is apparent. At the presently arid and xeric Marmes site in the Columbia Basin of southeastern Washington State, megafauna were absent by about 13,000calyr BP, evenness of small mammals declined about 11,700calyr BP and again about 11,400calyr BP whereas richness declined about 11,400cal BP. Regional faunal turnover was, however, minimal among small-bodied taxa. Local mammal communities are depauperate as a result of megafaunal extinctions and subsequent decreases in small-mammal richness and evenness. The latter chronologically corresponds with a decrease in primary productivity driven by increasing warmth and aridity. More faunas must be studied in order to fully document the range of variability in the responses of mammalian communities to PHT warming. Documentation of patterns in those responses will facilitate understanding and enhance predictive accuracy with respect to responses of mammalian communities to modern global warming.

Elk herbivory alters small mammal assemblages in high‐elevation drainages

Heavy herbivory by ungulates can substantially alter habitat, but the indirect consequences of habitat modification for animal assemblages that rely on that habitat are not well studied. This is a particularly important topic given that climate change can alter plant-herbivore interactions. We explored short-term responses of small mammal communities to recent exclusion of Rocky Mountain elk (Cervus elaphus) in high-elevation riparian drainages in northern Arizona, where elk impacts on vegetation have increased over the past quarter century associated with climate change. We used 10-ha elk exclosures paired with unfenced control drainages to examine how browsing influenced the habitat use, relative abundance, richness and diversity of a small mammal assemblage. We found that the small mammal assemblage changed significantly after 5years of elk exclusion. Relative abundance of voles (Microtus mexicanus) increased in exclosure drainages, likely due to an increase in habitat quality. The relative abundances of woodrats (Neotoma neomexicana) and two species of mice (Peromyscus maniculatus and P.boylii) decreased in the controls, while remaining stable in exclosures. The decline of mice in control drainages was likely due to the decline in shrub cover that they use. Thus, elk exclusion may have maintained or improved habitat for mice inside the exclosures while habitat quality and mouse abundance both declined outside the fences. Finally, small mammal species richness increased in the exclosures relative to the controls while species diversity showed no significant trends. Together, our results show that relaxation of heavy herbivore pressure by a widespread native ungulate can lead to rapid changes in small mammal assemblages. Moreover, exclusion of large herbivores can yield rapid responses by vegetation that may enhance or maintain habitat quality for small mammal populations.

Woodland Recovery after Suppression of Deer: Cascade effects for Small Mammals, Wood Mice (Apodemus sylvaticus) and Bank Voles (Myodes glareolus)

Over the past century, increases in both density and distribution of deer species in the Northern Hemisphere have resulted in major changes in ground flora and undergrowth vegetation of woodland habitats, and consequentially the animal communities that inhabit them. In this study, we tested whether recovery in the vegetative habitat of a woodland due to effective deer management (from a peak of 0.4–1.5 to <0.17 deer per ha) had translated to the small mammal community as an example of a higher order cascade effect. We compared deer-free exclosures with neighboring open woodland using capture-mark-recapture (CMR) methods to see if the significant difference in bank vole (Myodes glareolus) and wood mouse (Apodemus sylvaticus) numbers between these environments from 2001–2003 persisted in 2010. Using the multi-state Robust Design method in program MARK we found survival and abundance of both voles and mice to be equivalent between the open woodland and the experimental exclosures with no differences in various metrics of population structure (age structure, sex composition, reproductive activity) and individual fitness (weight), although the vole population showed variation both locally and temporally. This suggests that the vegetative habitat - having passed some threshold of complexity due to lowered deer density - has allowed recovery of the small mammal community, although patch dynamics associated with vegetation complexity still remain. We conclude that the response of small mammal communities to environmental disturbance such as intense browsing pressure can be rapidly reversed once the disturbing agent has been removed and the vegetative habitat is allowed to increase in density and complexity, although we encourage caution, as a source/sink dynamic may emerge between old growth patches and the recently disturbed habitat under harsh conditions.

Long-Term Response of Small Mammal Communities to the 1988 Huckleberry Mountain Fire

Biologists have long been interested in the response of small mammals and their habitat following natural disturbances. The Greater Yellowstone Area (GYA) fires of 1988 have provided opportunities to study short and long term responses. This study continues investigations conducted in the 1990’s following identical methodology at the same sites now 21 years post-fire. We live trapped 256 Clethrionomys gapperi (Red-backed Vole), 116 Peromyscus maniculatus (Deer Mouse), 44 Tamius minimus (Least Chipmunk), 28 Zapus princeps (Western Jumping Mouse), two Microtus montanus (Montane Vole), 1 Thomomys talpoides (Northern Pocket Gopher) and 37 shrews (Sorex ssp.). These results support findings from other investigations regarding the initial early dominance of P. maniculatus in burn areas and C. gapperi in control or non-burn areas, and as time has progressed since the burn, differences between burn and control sites (as measured by community diversity indices) has decreased. As expected calculated Shannon diversity indices (H’) in 2009 are higher for at least one of the burn sites than in previous years as the habitat recovers to pre-burn conditions.

Powerline corridors: degraded ecosystems or wildlife havens?

Management of powerline corridors in Australia has traditionally focused on the complete removal of vegetation using short rotation times owing to the perceived hazard of fire associated with corridor vegetation. Because of the intense management associated with fire hazards, little thought has been given to use of powerline corridors by wildlife. This has resulted in corridors traditionally being viewed as a source of fragmentation and habitat loss within forested ecosystems. We investigated the responses of small mammal communities living in a powerline corridor to management-induced vegetation changes at different successional stages, to determine whether a compromise could be reached between managing corridors for fire and biodiversity. Habitat modelling in the corridor and adjacent forest for three native and one introduced small mammal species demonstrated that species responded to changes in vegetation structural complexity, rather than time-since-management per se. Early seral stages of vegetation recovery after corridor management encouraged the introduced house mouse (Mus domesticus) into corridors and contributed little to biodiversity. Mid-seral-stage vegetation, however, provided habitat for native species that were rare in adjacent forest habitats. As the structural complexity of the vegetation increased, the small mammal community became similar to that of the forest so that corridor vegetation contributed fewer biodiversity benefits while posing an unacceptable fire risk. If ecologically sensitive management regimes are implemented to encourage mid-seral vegetation and avoid complete vegetation removal, powerline corridors have the potential to improve biodiversity. This would maintain landscape connectivity and provide habitat for native species uncommon in the forest while still limiting fuel loads in the corridor.

Efectos de la Extracción de Maderas sobre la Diversidad de Mamíferos Pequeños en Bosques de Tierras Bajas de la Guayana Venezolana1

The responses of small mammal communities to forest disturbance by logging were evaluated. The study area was located in the Imataca Forest Reserve (Venezuelan Guayana Region), where vegetation was predominantly lowland rain forest. Field analyses were based on a comparative inventory of species inhabiting primary forests and areas disturbed by selective logging. The taxonomic groups used as indicators of the ecological impact of logging belonged to the orders Didelphimorphia, Chiroptera, and Rodentia (families Sciuridae, Muridae, and Echimyidae). The following sampling methods were used: (1) mist nets; (2) traps in 2.4 ha grids (each with 120 stations: 60 at ground level and 60 in trees); and (3) diurnal and nocturnal sight surveys. Total sampling effort consisted of 1904 net-hours, 10,320 trap-nights, and 567 h of direct observations. At least 83 mammalian species inhabited the evaluated forests (74.7 percent corresponding to Chiroptera), of which 15.3 percent were restricted to primary forest. In logged areas, small mammal communities were characterized by: (1) higher abundances of individuals; (2) lower proportions of carnivorous and gleaning insectivorous bats; (3) increases in the relative abundance of frugivorous bat species that eat the fruits of colonizing plants; (4) higher proportions of aerial insectivores (Molossidae) at the lowest levels of the forest; (5) simplification in trophic structure of non-volant species, with semiarboreal predator-omnivores being the dominant guild (followed by terrestrial frugivore-omnivores); and (6) reduction in the relative abundance of mainly canopy-associated species. These results are explained by: (1) lower availability of key resources associated with primary forest (e.g., roosts in hollow trunks of mature trees, canopy fruits, and tree-crown continuity); (2) higher relative abundance of some food resources, such as terrestrial invertebrates and saprophytic plants, principally in areas where primary production is limited by low-fertility soils; (3) increase of roosting sites under fallen trunks; (4) modification of microclimatic conditions at the understory level as a consequence of a greater incident sunlight after canopy opening; and (5) increase in density of early successional plants. The implications of these results to the conservation of biodiversity in forests managed for timber extraction in the Venezuelan Guayana Region are discussed.

Long-Term Response of Small Mammal Communities to the 1988 Huckleberry Mountain Fire

Natural burns are common in the boreal forests of the Rocky Mountains. While a considerable amount of research has focused on post-burn responses of vegetation and, more recently, large mammals, there have been few studies on responses of small mammal communities in these forests. The primary objective of this study was to revisit study sites on Huckleberry Mountain established immediately following the 1988 Yellowstone fires (Stanton et al., 1991, 1992; Spildie, 1994) to assess small mammal population trends, community structure, and microhabitat preferences on adjacent burned and unburned study sites 9 years post-burn.

Comparison of small-mammal community responses to broadcast burning and herbicide application in cutover forest habitats

This study was designed to compare the responses of small-mammal communities to broadcast burning and herbicide-induced alteration of forest habitats. Study areas were located in south-coastal British Columbia, Canada, in the Coastal Western Hemlock (CWHdm) biogeoclimatic zone, and in west-central British Columbia in the Sub-boreal Spruce (SBSmk) and Engelmann Spruce–Subalpine Fir (ESSFmc) zones. Control–treatment comparisons for a herbicide application or a broadcast burning treatment were conducted at the coastal study area from 1982 to 1984. Replicate control–treatment comparisons between these two silvicultural practices were conducted at the interior study area within the period 1989 to 1992. Small-mammal populations were intensively livetrapped in all control and treatment blocks. Deer mouse (Peromyscusmaniculatus Wagner) populations showed short-term (1–2 months) declines after treatments at the coastal study area but appeared little affected by these habitat alterations at the interior area. Voles of the genus Microtus disappeared from burned blocks at the interior area but Microtusoregoni (Merriam) persisted on the burned block at the coastal area; however, the red-backed vole (Clethrionomysgapperi Vigors) did not. Chipmunks (Eutamiastownsendii Bachman and Eutamiasamoenus Allen) were little affected by either treatment. Neither treatment seemed to affect species diversity of these small-mammal communities. In terms of abundance of small-mammal populations, it is likely that broadcast burning is a more extreme means of habitat alteration than herbicide treatment.

Response of a Small Mammal Community to Water and Nitrogen Treatments in a Shortgrass Prairie Ecosystem

The response of small mammal communities to continuous water and nitrogen treatments on 1 hectare (ha) plots of shortgrass prairie was monitored over a 4 year period. Small mammals were live-trapped 18 times on each of eight plots representing water, nitrogen, water plus nitrogen, and control treatments. Four species ( Microtus ochrogaster , Onychomys leucogaster, Peromyscus maniculatus , and Spermophilus tridecemlineatus ) were captured. Analysis of variance with the variability in population densities (individuals/ha) partitioned between treatments and sample dates indicates significant treatment effects for all four species. Population densities of Microtus and Peromyscus were significantly higher (P < .001 and F < .02, respectively) on the water plus nitrogen treatment than on other treatments; Onychomys populations were significantly higher ( P < .05) on the nitrogen and control treatments than on the water and water plus nitrogen treatments; Spermophilus populations were significantly higher ( P < .05) on the nitrogen and control treatments than on the water plus nitrogen treatment. Analysis of variability in total small mammal biomass (grams, g, live weight/ha) also indicates significant treatment effects. Total biomass on the water plus nitrogen treatment was significantly higher ( P < .001) than on other treatments. Proportional species composition of the small mammal communities differed, with Microtus occurring primarily on the two “wet” treatments, Onychomys occurring primarily on the two “dry” treatments, and Peromyscus and Spermophilus occurring on all treatments. The ratio of community respiration to community consumption on the water plus nitrogen treatment, and to a lesser extent on the water treatment, is lower than on the nitrogen and control treatments as a result of the higher proportion of grazing herbivores (that is, Microtus ) on these treatments. Small mammal utilization of food resources never exceeded 4 percent of the available plants or 34 percent of the available arthropods on any of the treatments. Results tentatively support the hypothesis that changes in the small mammal communities were tightly coupled to changes in vegetation structure.