Good Predictor Of Abundance Research Articles

Hydroperiod of temporary ponds threats amphibian recruitment in Mediterranean environments

Abstract Climate change threatens amphibians because they depend on water availability. The amount of time that a pond is filled with water – the hydroperiod – may play an important role in larval development and recruitment. Nevertheless it is usually not taken into account when predicting future species trends. We evaluated the role of the hydroperiod in the abundance of five amphibian species in temporal ponds of a Moroccan forest during a seven-year period. Particularly, we characterized the ponds and compared the climatic variables affecting our system with the previous eight-year period. We tested the relationship between rainfall and hydroperiod, and we identified the best predictor of amphibian abundance. Our data showed that the last seven years were drier than the previous eight, being three of them so dry that none of the amphibian species bred successfully in those seasons. We demonstrated that hydroperiod was the best predictor of the abundance of amphibian species and affected the amphibian community composition. The rainfall was correlated with the hydroperiod and the number of ponds filled. Species with long larval periods such as the endangered Moroccan spadefoot toad and the sharp ribbed newt might be more vulnerable to climate change since they need longer hydroperiods to develop. However, widespread species with shorter hydroperiods such as the Mauretanian toad or the stripeless tree frog might be favoured. In order to predict accurately amphibian species trend under climate change scenarios and to develop adequate conservation strategies, hydroperiod should be considered in both the models and mitigation actions.

Both Landsat‐ and LiDAR‐derived measures predict forest bee response to large‐scale wildfire

AbstractLarge‐scale disturbances such as wildfire can have profound impacts on the composition, structure, and functioning of ecosystems. Bees are critical pollinators in natural settings and often respond positively to wildfires, particularly in forests where wildfire leads to more open conditions and increased floral resources. The use of Light Detection and Ranging (LiDAR) provides opportunities for quantifying habitat features across large spatial scales and is increasingly available to scientists and land managers for post‐fire habitat assessment. We evaluated the extent to which LiDAR‐derived forest structure measurements can predict forest bee communities after a large, mixed‐severity fire. We hypothesized that LiDAR measurements linked to post‐fire forest structure would improve our ability to predict bee abundance and species richness when compared to satellite‐based maps of burn severity. To test this hypothesis, we sampled wild bee communities within the Douglas Fire Complex in southwestern Oregon, USA. We then used LiDAR and Landsat data to quantify forest structure and burn severity, respectively, across bee sampling locations. We found that the LiDAR forest structure model was the best predictor of abundance, whereas the Landsat burn severity model had better predictive ability for species richness. Furthermore, the Landsat burn severity model was better at predicting the presence and species richness of bumble bees (Bombus spp.), an ecologically distinct and economically important group within the Pacific Northwest. We posit that the divergent responses of the two modeling approaches are due to distinct responses by bee taxa to variation in forest structure as mediated by wildfire, with bumble bees in particular depending on closed‐canopy forest for some portions of their life cycle. Our study demonstrates that LiDAR data can provide information regarding the drivers of bee abundance in post‐wildfire conifer forest, and that both remote sensing approaches are useful for predicting components of wild bee diversity after large‐scale wildfire.

Influence of water's physical and chemical parameters on mosquito (Diptera: Culicidae) assemblages in larval habitats in urban parks of São Paulo, Brazil

Water's physical and chemical characteristics are important constraints in aquatic ecosystems, acting on the development, survival, and adaptation of different organisms. Immature forms of mosquitoes develop in widely diverse aquatic environments and are mainly found in permanent or temporary freshwater bodies with little or no movement. The current study aimed to investigate whether variations in larval habitats’ pH, salinity, dissolved oxygen, and water temperature influence the composition of Culicidae assemblages and the presence and abundance of Aedes albopictus and Ae. aegypti. From August 2012 to July 2013, captures of immature forms and measurement of water's physical and chemical profiles were performed monthly in natural and artificial breeding sites in four urban parks in the city of São Paulo, Brazil. Changes in species composition related to the parameters’ variation were assessed by multivariate analysis. Regression trees were performed to evaluate the effect of breeding sites’ physical and chemical variations on the presence and abundance of Ae. albopictus and Ae. aegypti. The observations suggest ranges of conditions for the measured variables in which most species tend to be found more frequently, and pH and salinity are the variables most closely associated with variations in mosquito composition. Ae. aegypti and Ae. albopictus were present in both natural and artificial breeding sites and were observed under significantly varying conditions of pH, salinity, dissolved oxygen, and temperature. For Ae. albopictus, larval habitat type and pH were the best predictors of incidence and abundance. For Ae. aegypti, pH and salinity were the best predictors of abundance, while dissolved oxygen and larval habitat type were better predictors of presence. This information broadens our understanding of the ecology and interaction of the investigated species with abiotic factors in the aquatic environments, providing useful data for studies that seek to elucidate the underlying mechanisms of selection and colonization of breeding sites by these mosquitoes. This study also reinforces previous observations indicating that Ae. albopictus and Ae. aegypti can colonize diverse types of larval habitats with widely varying physical and chemical conditions.

Context‐dependent biotic interactions control plant abundance across altitudinal environmental gradients

Many biotic interactions influence community structure, yet most distribution models for plants have focused on plant competition or used only abiotic variables to predict plant abundance. Furthermore, biotic interactions are commonly context‐dependent across abiotic gradients. For example, plant–plant interactions can grade from competition to facilitation over temperature gradients. We used a hierarchical Bayesian framework to predict the abundances of 12 plant species across a mountain landscape and test hypotheses on the context‐dependency of biotic interactions over abiotic gradients. We combined field‐based estimates of six biotic interactions (foliar herbivory and pathogen damage, fungal root colonization, fossorial mammal disturbance, plant cover and plant diversity) with abiotic data on climate and soil depth, nutrients and moisture. All biotic interactions were significantly context‐dependent along temperature gradients. Results supported the stress gradient hypothesis: as abiotic stress increased, the strength or direction of the relationship between biotic variables and plant abundance generally switched from negative (suggesting suppressed plant abundance) to positive (suggesting facilitation/mutualism). For half of the species, plant cover was the best predictor of abundance, suggesting that the prior focus on plant–plant interactions is well‐justified. Explicitly incorporating the context‐dependency of biotic interactions generated novel hypotheses about drivers of plant abundance across abiotic gradients and may improve the accuracy of niche models.

On the controls of abundance for soil‐dwelling organisms on the Tibetan Plateau

AbstractAfter decades of research, we are starting to understand more about why the number of species varies from place to place on the planet. However, little is known about spatial variation in abundance, especially for soil‐dwelling organisms. In this study, we aimed to disentangle the relative influences of climatic factors, soil properties, and plant diversity on the abundance of soil‐dwelling invertebrates (i.e., nematodes and soil arthropods) at 48 alpine grassland sites on the Tibetan Plateau. We found that the abundance of these two groups of soil organisms was negatively correlated with soil pH and temperature seasonality, and was positively correlated with soil organic carbon (SOC), mean annual precipitation, and plant species richness; there was no effect of mean annual temperature or seasonality in precipitation on the abundance of nematodes or soil‐dwelling arthropods. When we considered only the nematodes, we found that soil pH, mean annual precipitation, temperature seasonality, and SOC were the best predictors of abundance. However, plant species richness was the best predictor of the abundance of soil‐dwelling arthropods. Different orders within the arthropods responded differently to the suite of factors we examined. Taken together, our results suggest that increases in temperature alone might not alter the abundances of soil organisms in these alpine grasslands. Instead, altered precipitation regimes and increases in intra‐annual variation in temperature, changes in plant community diversity, and the resulting changes in soil characteristics (e.g., pH and organic carbon) could reshape soil communities in the Tibetan grassland ecosystems, and likely elsewhere on the planet.

Heterogeneous patterns of abundance of epigeic arthropod taxa along a major elevation gradient

AbstractSpecies diversity is the variable most commonly studied in recent ecological research. Ecological processes, however, are driven by individuals and affected by their abundances. Understanding the variation in animal abundances along climatic gradients is important for predicting changes in ecosystem processes under global warming. High abundances make arthropods, despite their small body sizes, important actors in food webs, yet abundance distributions of major arthropod taxa along climatic gradients remain poorly documented. We sampled arthropod assemblages in disturbed and undisturbed vegetation types along an elevational gradient of 860–4550 m asl on the southern slopes of Mt. Kilimanjaro, Tanzania. In our analysis, we focused on 13 taxa of arthropods that represented three major functional groups: predators, herbivores, and decomposers. Abundance patterns were unimodal for most of the taxa and functional groups, including decomposer arthropods, and most of them peaked at low elevations in lower montane forest. When we assigned beetles to functional groups, however, decomposer beetle abundances declined almost linearly, and abundances of predator beetles (ca. 2400 m asl) and herbivore beetles (ca. 3000 m asl, undisturbed vegetation) peaked at higher elevations and exhibited unimodal patterns. Temperature, not primary productivity, was the best predictor of abundance for most of the taxa and groups. Disturbance was only of minor importance. Our results revealed different trends in the response of arthropod abundance along the elevational gradient that depended on the level of taxonomic and functional resolution. This highlights the need for more comparisons of different taxa along the same climatic gradients.

Identifying opportunities for conservation embedded in cropland anthromes

Anthromes characterize terrestrial ecological patterns in terms of human populations and how these populations use the land. However, data are needed to assess the conservation value of habitats embedded in anthromes, particularly when possible conservation opportunities do not reflect the traditional focus of conservation in a region. One such region is the central Great Plains of North America where the grassland biome has been replaced by a cropland anthrome with a landscape mosaic dominated by arable crops with small patches of grass and woody cover embedded within. Grassland birds have been the primary focus of avian conservation research and practice, a reflection of the biome classification. Yet conservation of other bird species may be a missed conservation opportunity better identified via anthromes. In this project we evaluated the variation in abundance of shrubland and open forest birds in response to heterogeneity and availability of woody and grass cover at local (100 m) and landscape (5,000 m) scales. We found that local heterogeneity, a trait of croplands not grasslands, was the best predictor of abundance, with five species of conservation concern more abundant in heterogeneous sites. There was limited response to woody cover and a mixed response across scale to grassland cover with local response positive and landscape negative. These data suggest that increasing heterogeneity in the Great Plains cropland anthrome may provide a unique conservation opportunity. In particular, farm systems have the capacity to complement regional species conservation efforts by increasing heterogeneity. Importantly these conservation efforts may not come at the expense of grassland bird conservation or crop production. The limited response to extensive grassland cover at the larger scale suggests that in Great Plains agroecosystems, a diverse mix of crops, pasture, and linear habitats would allow farmers to continue to produce food while contributing to the conservation of species of concern.

Abundance modelling of invasive and indigenous Culicoides species in Spain

In this paper we present a novel methodology applied in Spain to model spatial abundance patterns of potential vectors of disease at a medium spatial resolution of 5 x 5 km using a countrywide database with abundance data for five Culicoides species, random regression Forest modelling and a spatial dataset of ground measured and remotely sensed eco-climatic and environmental predictor variables. First the probability of occurrence was computed. In a second step a direct regression between the probability of occurrence and trap abundance was established to verify the linearity of the relationship. Finally the probability of occurrence was used in combination with the set of predictor variables to model abundance. In each case the variable importance of the predictors was used to biologically interpret results and to compare both model outputs, and model performance was assessed using four different accuracy measures. Results are shown for C. imicola, C. newsteadii, C. pulicaris group, C. punctatus and C. obsoletus group. In each case the probability of occurrence is a good predictor of abundance at the used spatial resolution of 5 x 5 km. In addition, the C. imicola and C. obsoletus group are highly driven by summer rainfall. The spatial pattern is inverse between the two species, indicating that the lower and upper thresholds are different. C. pulicaris group is mainly driven by temperature. The patterns for C. newsteadii and C. punctatus are less clear. It is concluded that the proposed methodology can be used as an input to transmission-infection-recovery (TIR) models and R0 models. The methodology will become available to the general public as part of the VECMAP™ software.

Body size of Chrysomelidae (Coleoptera, Insecta) in areas with different levels of conservation in South Brazil

Body size is correlated with many species traits such as morphology, physiology, life history and abundance as well; it is one of the most discussed topics in macroecological studies. The aim of this paper was to analyze the body size distribution of Chrysomelidae, caught with Malaise traps during two years in four areas with different levels of conservation in the Araucaria Forest, Paraná, Brazil, determining if body size is a good predictor of abundance, and if body size could be used to indicate environmental quality. Body size was considered the total length of the specimen from the anterior region of head to the apex of abdomen/elytron. Measurements were taken for up to ten specimens of each species for each area and for all specimens of those species represented by fewer than ten individuals. The highest abundance and richness of Chrysomelidae were obtained in the lowest body size classes. This herbivorous group showed a trend toward a decrease in body size with increasing abundance, but body size was not a good predictor of its abundance. There was a trend toward a decrease in body size from the less to the most conserved areas; however, the definition of a pattern in successional areas not seems to be entirely clear.

Abundance of Helicoverpa zea1,and Heliothis virescens1in Pheromone Traps During the Past Twenty Years in Northwestern Louisiana

Populations of the bollworm, Helicoverpa zea (Boddie), and the tobacco budworm, Heliothis virescens (F.), were monitored with pheromone-baited wire cone traps on the Red River Research Station from 1986 to 2005. Data are presented on population variation and changes observed during the sampling period for the months of May through August. Bollworm moths made up 87.8, 79.0, 82.7, and 63.5% of the total number of male moths captured in May through August, respectively. Overall, 76.3% of the male moths captured from May though August were bollworms. The abundance of bollworms in pheromone traps indicated considerable variation on a yearly and monthly basis. The number of bollworms captured in traps and an analysis of variance provided no evidence that the introduction of Bt cotton in 1996 had any significant effect on bollworm abundance at this location. However, abundance of tobacco budworm has been decreasing since approximately 1993–1994. Analysis of variance confirmed that abundance of male tobacco budworms caught in traps was significantly less post-Bt cotton (1997–2005) compared with the pre-Bt cotton period (1986–1996). However, the analysis also indicated that abundance of tobacco budworms had been decreasing significantly before commercialization of Bt cotton in 1996. The decline did not seem to have increased since the introduction of Bt cotton although bollworm abundance still is decreasing. The decline in tobacco budworm abundance in this study seems to have begun before the introduction of Bt cotton. It is still possible that the duration and significance of the decline is related in some way to the introduction of Bt cotton in 1996, or the decline could be the result of normal variation and/or population cycles of a length that cannot be ascertained due to the length of the sampling period in this study. Regression analyses indicated that numbers of tobacco budworm in any given month were a good predictor of abundance in subsequent months. This was not true for abundance of bollworm.

Rainfall influences on ungulate population abundance in the Mara‐Serengeti ecosystem

1. Rainfall is the prime climatic factor underpinning the dynamics of African savanna ungulates, but no study has analysed its influence on the abundance of these ungulates at monthly to multiannual time scales. 2. We report relationships between rainfall and changes in age- and sex-structured abundances of seven ungulate species monitored monthly for 15 years using vehicle ground counts in the Maasai Mara National Reserve, Kenya. 3. Abundance showed strong and curvilinear relationships with current and cumulative rainfall, with older topi, Damaliscus korrigum (Ogilby); warthog, Phacochoerus aethiopicus (Pallas); waterbuck, Kobus ellipsyprimnus (Ogilby); and impala, Aepyceros melampus (Lichtenstein) responding to longer lags than younger animals, portraying carryover effects of prior habitat conditions. 4. The abundances of newborn calves were best correlated with monthly rainfall averaged over the preceding 5-6 months for topi, waterbuck, warthog, and 2 months for the migratory zebra Equus burchelli (Gray), but with seasonal rainfall averaged over 2-5 years for giraffe, Giraffa camelopardalis (L.); impala; and kongoni, Alcelaphus busephalus (Pallas). The cumulative late wet-season rainfall was the best predictor of abundance for quarter- to full-grown animals for most species. Monthly rainfall exerted both negative and positive effects on the abundances of zebra, impala and waterbuck. Ignoring age, both sexes responded similarly to rainfall. 5. Births were strongly seasonal only for warthog and topi, but peaked between August and December for most species. Hence abundance was strongly seasonal for young topi and warthog and the migratory zebra. Pronounced seasonality in births for warthog and topi obliterated otherwise strong relationships between abundance and rainfall when both month and rainfall were included in the same model. Aggregated density produced relationships with rainfall similar to those for fully grown animals, emphasizing the necessity of demographic monitoring to reliably reveal rainfall influences on ungulate abundance in the Mara. 6. Strong relationships between abundance and rainfall suggest that rainfall underpins the dynamics of African savanna ungulates, and that changes in rainfall due to global warming may markedly alter the abundance and diversity of these mammals. Ungulates respond to rainfall fluctuations through movements, reproduction or survival, and the responses appear independent of breeding phenology and synchrony, dietary guild, or degree of water dependence. Newborns and adults have contrasting responses to rainfall. Males and females respond similarly to rainfall when age is ignored.

THE INFLUENCE OF INTERSPERSION ON MARSH BIRD ABUNDANCE IN NEW YORK

Abstract Interspersion is a key habitat component related to marsh bird abundance, but is not easily quantified. We used Fragstats 3.3 and aerial photos to measure interspersion within wetlands as m/ha of interface between vegetation and water (i.e., edge density). We then related edge density and other factors (marsh area, cover-to-water ratios, marsh area within 5 km) to the abundance of marsh birds on 16 emergent wetlands in New York during 2005. Abundance was assessed via call broadcast surveys for American Bittern (Botaurus lentiginosus), Least Bittern (Ixobrychus exilis), Pied-billed Grebe (Podilymbus podiceps), Sora (Porzana carolina), and Virginia Rail (Rallus limicola). Interspersion, as measured by edge density, was the best predictor of abundance for all species but Pied-billed Grebe (r2 = 0.30–0.71). Vegetation and water interspersed in a spatially complex pattern likely increases breeding diversity and density of marsh birds. Modern spatial analysis programs provide opportunities to quantify ...

Predicting Species Abundance in the Face of Habitat Loss

Predicting Species Abundance in the Face of Habitat Loss

Habitat Matrix Effects on Pond Occupancy in Newts

Abstract: In farmlands, the population viability of many amphibians is suspected to depend on the resistance the matrix of crop fields presents to movements between ponds and terrestrial sites and movements among ponds. Over recent decades the increase in cereal growing at the expense of cattle breeding has caused a drastic change in habitat matrix in many European regions. We investigated the effect of such change on populations of three newt species ( Triturus helveticus, T. alpestris, and T. cristatus) by comparing their abundances in sites that varied in amount of cultivated ground. A multivariate regression analysis of the relationship of newt abundance to both pond and landscape variables demonstrated the negative influence of cultivated ground on abundance. The width of the uncultivated sector linking the pond to the forest was a good predictor of abundance after the influences of both pond area and fish presence were removed. Moreover, newt presence was positively related to the number of ponds within that 50‐ha surrounding area, highlighting the role of metapopulation functioning in newt occupancy of ponds. The relationship between newt abundance and width of uncultivated sectors agrees with present knowledge of the orientation mechanisms that underlie migration movements in urodeles. Such a relationship between connectedness and sector width shows that narrow, linear corridors such as hedgerows may not be useful in newt conservation. Our study also highlights the need to incorporate a behavioral component of habitat use into models of connectivity in conservation biology.

Disparate determinants of summer and winter diet selection of a generalist herbivore, Ochotona princeps.

The North American pika, Ochotona princeps, is a generalist herbivore that simultaneously selects two distinct diets: one consumed immediately (summer diet), the other harvested, transported, and stored for later consumption (winter diet). I investigated factors influencing diet selection at two sites on the West Knoll of Niwot Ridge, Boulder County, Colorado during 1991 and 1992. The composition of summer and winter diets differed significantly from each other as well as from the relative abundance of food items in the environment. Thus, pikas were not foraging randomly for either diet. To explore winter and summer diet selection, I tested two existing hypotheses: (1) that plant morphology restricts the winter diet breadth to plants that are easily harvested and large, and thereby maximizes the amount collected per foraging effort, or (2) to compensate for nutrients lost during storage, pikas bias their winter diet with high-nutrient species. I also tested the hypothesis that plant secondary compounds may be higher in the winter diet either because they function as preservatives or because pikas delay consumption of these species until the toxins degrade. For individual dietary items, I measured energy, nitrogen, water, fiber, total phenolic, condensed tannin, and astringency contents. There was little evidence to suggest that morphology excluded plants from the winter diet. Plant size was not a good predictor of abundance in the winter diet. Even after harvesting costs had been experimentally removed, cushion plants were still not included in the winter diet. There was weak support for an effect of nutrients on winter diet selection; in three of four cases, the winter diet was significantly lower in water and higher in total energy content as predicted by the nutrient compensation hypothesis. However, other nutrients exhibited no consistent pattern. Nutrients were not reliable predictors of the winter diet in multiple regression analyses. There was strong support for the hypothesis of manipulation of secondary compounds. The winter diet was significantly higher in total phenolics and astringency. Total phenolics were consistent predictors of the winter diet in multiple regression analyses. The winter diets of six additional pika populations contained plant species high in secondary compounds. The results suggest that pikas preferentially select plants with high levels of secondary compounds for their winter diet, possibly because the presence of such compounds promotes preservation of the cache. This behavior may also enable the exploitation of an otherwise unusable food resource, i.e., toxic plants.

Abundance and Body Size in British Birds: Reconciling Regional and Ecological Densities

Considerable attention has recently focused on the use of species body size as a predictor of species abundance, with consensus lacking over whether or not size is a useful predictor (Blackburn et al. 1993, Cotgreave 1993, Currie 1993, Damuth 1993, Blackburn and Lawton 1994). Initial studies of the relationship between body mass and abundance across species, plotted on logarithmic axes, suggested that the two were highly correlated (Damuth 1981, 1987, Peters 1983, Peters and Wassenberg 1983, Peters and Raelson 1984). Body mass generally explained around 60% of the variation in abundance across species. The strength of the size:abundance correlation gave rise to the view that a species' abundance was set by its body size, and therefore that body size is a good predictor of abundance (Damuth 1981, Peters 1983). This view has been criticised (Brown and Maurer 1986, 1987, Lawton 1989, 1991, Blackburn et al. 1993, Blackburn and Lawton 1994). Negative size:abundance relationships have generally been shown in data compiled from singleor few-species studies (e.g. Damuth 1987), and thus may not be representative of the situation in whole animal assemblages. The contribution to these relationships of rare species and low density populations of common species, both of which are rarely studied, is likely to have been underestimated (Brown and Maurer 1987, Morse et al. 1988, Lawton 1989, 1991). Subsequent studies sampling whole assemblages of taxonomically similar animals revealed different, polygonal relationships between log body size and log abundance, with intermediate-sized species having peak abundance (Brown and Maurer 1987, Gaston 1988, Gaston and Lawton 1988, Morse et al. 1988, Cotgreave et al. 1993). These polygons generally showed either no overall correlation between body size and population abundance (Morse et al. 1988) or a weak negative relationship, with body size generally explaining less than 10% of the variation in abundance (Brown and Maurer 1987, Gaston and Lawton 1988, Blackburn et al. 1993). Whole assemblage studies gave rise to an alternative view, that species body size is a poor predictor of species abundance (Blackburn et al. 1993). Conclusions from whole assemblage samples, however, have in turn been criticised (Damuth 1991, Currie 1993). Abundances in samples from assemblages tend to be veiled (Nee et al. 1991a). Many species will be represented in abundance samples by a single individual. This is unlikely to be the true abundance of the species, but rather the result of incomplete sampling. Therefore, the true abundances of the rarest species in these assemblages are not revealed by the samples (Currie 1993). In addition, samples may include transient individuals from species not otherwise resident in the assemblage, inflating the number of apparently rare species observed (although the presence of transients did not significantly change the size:abundance relationship in the one assemblage where their contribution has been tested (Gaston et al. 1993)). One major problem with reconciling the results of these different studies is that assemblage studies generally report species abundance using a different measure to compilation studies (Damuth 1991). Compilation studies generally compare species densities in suitable habitat ('ecological' density), whereas many, although not all (e.g. Gaston and Lawton 1988), assemblage studies compare species abundances in samples from a given area ('regional' or 'crude' density; Damuth 1991). Ecological density gives information about the abundance attained by a species within the habitat it occupies, but takes no account of how that area is distributed. Thus a species with a high ecological density might be very rare if it is adapted to a geographically restricted habitat. A comparison of regional densities, on the other hand, is a comparison of species abundances within a fixed area (e.g. birds within North America; Brown and Maurer 1987), and so