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Co-occurrence Patterns (co-occurrence + pattern)
Selected AbstractsCo-occurrence patterns of five species of anurans at a pond network in Victoria Lake, KenyaAFRICAN JOURNAL OF ECOLOGY, Issue 1 2010Leonardo Vignoli First page of article [source] Fire disturbance disrupts co-occurrence patterns of terrestrial vertebrates in Mediterranean woodlandsJOURNAL OF BIOGEOGRAPHY, Issue 5 2006Maurizio Sarà Abstract Aim, This paper uses null model analysis to explore the pattern of species co-occurrence of terrestrial vertebrate fauna in fire-prone, mixed evergreen oak woodlands. Location, The Erico,Quercion ilicis of the Mediterranean belt (50,800 m a.s.l.) in the Madonie mountain range, a regional park in northern Sicily (37°50, N, 14°05, E), Italy. Methods, The stratified sampling of vertebrates in a secondary succession of recent burned areas (BA, 1,2 years old), intermediate burned areas (INT, 4,10 years old) and ancient burned areas (CNB, > 50 years old), plus forest fragments left within burned areas (FF, 1,2 years old) permitted the comparison of patterns of species co-occurrence using a set of separate presence/absence matrices. First, the breeding avifauna derived from standardized point counts was analysed using Stone & Roberts'C -score, and by a null model algorithm (fixed/equiprobable). Secondly, the analysis was repeated using all vertebrate species recorded in the succession. Results, Sixty-five species were recorded in the 2-year study period in the four sample treatments. Birds were found to make up the largest component (63%) of the recorded assemblage. The BA treatment had the lowest species richness, followed in order by the small, medium and large FFs, and then by the CNBs. For both analyses (birds and total vertebrates), the C -scores were quite small and not significantly different from those that could be expected by chance in the BA and INT burned areas; this indicates a random co-occurrence among vertebrates of those assemblages. Contrariwise, for both analyses in the CNBs, the C -scores were large and significantly different from the simulated indices, thereby indicating a non-random co-occurrence pattern (segregation) of vertebrates in the undisturbed woodlands. In addition, C -score values for the surviving FFs show a significant aggregation of species. Main conclusions, The null model analyses highlighted a new aspect of fire disturbance in Mediterranean woodland ecosystems: the disruption in patterns of co-occurrence in the terrestrial vertebrate community. Wildfire alters community organization, inducing, for at least 10 years, a random aggregate of species. Communities re-assemble themselves, showing the occurrence of species segregation at least 50 years after fire. [source] Co-occurrence of ectoparasites of marine fishes: a null model analysisECOLOGY LETTERS, Issue 1 2002Nicholas J. Gotelli We used null model analysis to test for nonrandomness in the structure of metazoan ectoparasite communities of 45 species of marine fish. Host species consistently supported fewer parasite species combinations than expected by chance, even in analyses that incorporated empty sites. However, for most analyses, the null hypothesis was not rejected, and co-occurrence patterns could not be distinguished from those that might arise by random colonization and extinction. We compared our results to analyses of presence,absence matrices for vertebrate taxa, and found support for the hypothesis that there is an ecological continuum of community organization. Presence,absence matrices for small-bodied taxa with low vagility and/or small populations (marine ectoparasites, herps) were mostly random, whereas presence,absence matrices for large-bodied taxa with high vagility and/or large populations (birds, mammals) were highly structured. Metazoan ectoparasites of marine fishes fall near the low end of this continuum, with little evidence for nonrandom species co-occurrence patterns. [source] Biogeographic effects of red fire ant invasionECOLOGY LETTERS, Issue 4 2000N.J. Gotelli The red imported fire ant, Solenopsis invicta, was accidentally introduced to North America over 60 years ago and has spread throughout the southeastern United States. We document the biogeographic consequences of this invasion. We censused ground-foraging ant communities on a 2000 km transect from Florida through New York that passed through invaded and intact biotas. Native ant species density peaks at mid-latitudes in the eastern United States, and the location of this peak corresponds to the range limit of S. invicta. In uninvaded sites, ant species co-occur less often than expected by chance. In the presence of S. invicta, community structure converges to a random pattern. Our results suggest that the effects of S. invicta on native ant communities are pervasive: not only does the presence of S. invicta reduce species density at local scales, it alters the co-occurrence patterns of surviving species at a biogeographic scale. [source] Species co-occurrence, nestedness and guild,environment relationships in stream macroinvertebratesFRESHWATER BIOLOGY, Issue 9 20092Article first published online: 2 JUN 200, JANI HEINO Summary 1. Describing species distribution patterns and the underlying mechanisms is at the heart of ecological research. A number of recent studies have used null model approaches to explore mechanisms behind spatial variation in community structure. 2. However, unexplored questions are the degree to which single guilds of potentially competing stream macroinvertebrate species show: (i) interspecific segregation among-stream sites (i.e. occur together less often than expected by chance), suggesting competitive interactions; (ii) interspecific aggregation (i.e. occur together more often than expected by chance), suggesting similar responses to the environment; (iii) comply with nestedness, suggesting the existence of selective extinctions or colonisations and (iv) show similar environmental relationships. 3. The present analyses showed that guilds of stream macroinvertebrates exhibit non-random co-occurrence patterns that were generally contingent on the weighting of sites by stream size. Despite significant segregation of species, each guild also showed significantly nested patterns. Species richness was correlated with different environmental factors between the guilds, although these correlations were relatively low. By contrast, correlations between the major ordination axes and key environmental variables were slightly stronger in canonical correspondence analysis, and generally the same factors were most strongly correlated with variation in the species composition of each guild. 4. The present findings are the first to show that species within each stream macroinvertebrate guild show significant negative co-occurrence at the among-stream riffle scale. These findings present challenges for future studies that aim to disentangle whether these patterns comply with the habitat checkerboard or the competitive checkerboard explanations. [source] Do community-level models describe community variation effectively?JOURNAL OF BIOGEOGRAPHY, Issue 10 2010Andrés Baselga Abstract Aim, The aim of community-level modelling is to improve the performance of species distributional models by taking patterns of co-occurrence among species into account. Here, we test this expectation by examining how well three community-level modelling strategies (,assemble first, predict later', ,predict first, assemble later', and ,assemble and predict together') spatially project the observed composition of species assemblages. Location, Europe. Methods, Variation in the composition of European tree assemblages and its spatial and environmental correlates were examined with cluster analysis and constrained analysis of principal coordinates. Results were used to benchmark spatial projections from three community-based strategies: (1) assemble first, predict later (cluster analysis first, then generalized linear models, GLMs); (2) predict first, assemble later (GLMs first, then cluster analysis); and (3) assemble and predict together (constrained quadratic ordination). Results, None of the community-level modelling strategies was able to accurately model the observed distribution of tree assemblages in Europe. Uncertainty was particularly high in southern Europe, where modelled assemblages were markedly different from observed ones. Assembling first and predicting later led to distribution models with the simultaneous occurrence of several types of assemblages in southern Europe that do not co-occur, and the remaining strategies yielded models with the presence of non-analogue assemblages that presently do not exist and that are much more strongly correlated with environmental gradients than with the real assemblages. Main conclusions, Community-level models were unable to characterize the distribution of European tree assemblages effectively. Models accounting for co-occurrence patterns along environmental gradients did not outperform methods that assume individual responses of species to climate. Unrealistic assemblages were generated because of the models' inability to capture fundamental processes causing patterns of covariation among species. The usefulness of these forms of community-based models thus remains uncertain and further research is required to demonstrate their utility. [source] Biogeography of Iberian freshwater fishes revisited: the roles of historical versus contemporary constraintsJOURNAL OF BIOGEOGRAPHY, Issue 11 2009Ana F. Filipe Abstract Aim, The question of how much of the shared geographical distribution of biota is due to environmental vs. historical constraints remains unanswered. The aim of this paper is to disentangle the contribution of historical vs. contemporary factors to the distribution of freshwater fish species. In addition, it illustrates how quantifying the contribution of each type of factor improves the classification of biogeographical provinces. Location, Iberian Peninsula, south-western Europe (c. 581,000 km2). Methods, We used the most comprehensive data on native fish distributions for the Iberian Peninsula, compiled from Portuguese and Spanish sources on a 20-km grid-cell resolution. Overall, 58 species were analysed after being categorized into three groups according to their ability to disperse through saltwater: (1) species strictly intolerant of saltwater (primary species); (2) species partially tolerant of saltwater, making limited incursions into saltwaters (secondary species); and (3) saltwater-tolerant species that migrate back and forth from sea to freshwaters or have invaded freshwaters recently (peripheral species). Distance-based multivariate analyses were used to test the role of historical (basin formation) vs. contemporary environmental (climate) conditions in explaining current patterns of native fish assemblage composition. Cluster analyses were performed to explore species co-occurrence patterns and redefine biogeographical provinces based on the distributions of fishes. Results, River basin boundaries were better at segregating species composition for all species groups than contemporary climate variables. This historical signal was especially evident for primary and secondary freshwater fishes. Eleven biogeographical provinces were delineated. Basins flowing to the Atlantic Ocean north of the Tagus Basin and those flowing to the Mediterranean Sea north of the Mijares Basin were the most dissimilar group. Primary and secondary freshwater species had higher province fidelity than peripheral species. Main conclusions, The results support the hypothesis that historical factors exert greater constraints on native freshwater fish assemblages in the Iberian Peninsula than do current environmental factors. After examining patterns of assemblage variation across space, as evidenced by the biogeographical provinces, we discuss the likely dispersal and speciation events that underlie these patterns. [source] Fire disturbance disrupts co-occurrence patterns of terrestrial vertebrates in Mediterranean woodlandsJOURNAL OF BIOGEOGRAPHY, Issue 5 2006Maurizio Sarà Abstract Aim, This paper uses null model analysis to explore the pattern of species co-occurrence of terrestrial vertebrate fauna in fire-prone, mixed evergreen oak woodlands. Location, The Erico,Quercion ilicis of the Mediterranean belt (50,800 m a.s.l.) in the Madonie mountain range, a regional park in northern Sicily (37°50, N, 14°05, E), Italy. Methods, The stratified sampling of vertebrates in a secondary succession of recent burned areas (BA, 1,2 years old), intermediate burned areas (INT, 4,10 years old) and ancient burned areas (CNB, > 50 years old), plus forest fragments left within burned areas (FF, 1,2 years old) permitted the comparison of patterns of species co-occurrence using a set of separate presence/absence matrices. First, the breeding avifauna derived from standardized point counts was analysed using Stone & Roberts'C -score, and by a null model algorithm (fixed/equiprobable). Secondly, the analysis was repeated using all vertebrate species recorded in the succession. Results, Sixty-five species were recorded in the 2-year study period in the four sample treatments. Birds were found to make up the largest component (63%) of the recorded assemblage. The BA treatment had the lowest species richness, followed in order by the small, medium and large FFs, and then by the CNBs. For both analyses (birds and total vertebrates), the C -scores were quite small and not significantly different from those that could be expected by chance in the BA and INT burned areas; this indicates a random co-occurrence among vertebrates of those assemblages. Contrariwise, for both analyses in the CNBs, the C -scores were large and significantly different from the simulated indices, thereby indicating a non-random co-occurrence pattern (segregation) of vertebrates in the undisturbed woodlands. In addition, C -score values for the surviving FFs show a significant aggregation of species. Main conclusions, The null model analyses highlighted a new aspect of fire disturbance in Mediterranean woodland ecosystems: the disruption in patterns of co-occurrence in the terrestrial vertebrate community. Wildfire alters community organization, inducing, for at least 10 years, a random aggregate of species. Communities re-assemble themselves, showing the occurrence of species segregation at least 50 years after fire. [source] Null model analysis of communities on gradientsJOURNAL OF BIOGEOGRAPHY, Issue 6 2004James G. Sanderson Abstract Aim, I employed a novel null model and metric to uncover unusual species co-occurrence patterns in a herpetofaunal assemblage of 49 species collected at discrete elevations along a gradient. Location, Mount Kupe, Cameroon. Methods, Using a construction algorithm that started from a matrix of 0s, a sample null space of 25,000 unique null matrices was generated by simultaneously conserving (1) the number of occurrences of each species, (2) site richness and (3) species range spans derived from the observed incidence matrix. I then compared the number of times each pair of confamilial species co-occurred in the null space with the same number derived from the observed incidence matrix. Two cases dealing with embedded absences in species ranges were tested: (1) embedded absences were maintained, and (2) embedded absences were assumed to be sampling omissions and were replaced by presences. Results, In the observed absence/presence assemblage there were 147 possible confamilial species pairs. Therefore, 5% or eight were expected by chance alone to have co-occurrence patterns that differed from chance expectations by chance alone. Of these confamilial species pairs, 38 were congeneric and so 5% or two were expected to differ from chance expectations. For case (1) 16, and for case (2) 17 confamilial species pairs' co-occurrence patterns differed significantly from chance expectations. For case (1) nine congeneric species pairs, and for case (2) 10 congeneric pairs differed significantly from chance expectations. For case (1) four, and for case (2) five congeneric species pairs formed checkerboards (patterns of mutual exclusion). Results from case (1) were a proper subset of case (2) indicating that sampling omissions did not alter greatly the results. Main conclusions, I have demonstrated that null models are valuable tools to analyse ecological communities provided that proper models are employed. The choice of the appropriate null space to analyse distributions is critical. The null model employed to analyse birds on islands of an archipelago can be adapted to analyse species along gradients provided an additional range constraint is added to the null model. Moreover, added precision to results can be obtained by analysing each species pair separately, particularly those in the same family or genus, as opposed to applying a community-wide metric to the faunal assemblage. My results support some of the speculations of previous authors who were unable to demonstrate their suspicions analytically. [source] Abundance and co-occurrence patterns of core and satellite species of ground beetles on small lake islandsOIKOS, Issue 2 2006Werner Ulrich 15 lake islands and two mainland sites of Mamry lake in Poland were sampled to investigate community structures and patterns of co-occurrences of ground beetles (Carabidae). The total ground beetle metacommunity of 71 species was divided into a group of core species occupying at least half of all study sites and of satellite species, which occurred at two sites or less. This division is mirrored by reduced dispersal abilities and non-random patterns of site occupancy. Core and satellite species also differed in patterns of relative abundance. The core group followed a lognormal distribution, the satellite group a power function as predicted by the self-similarity model of occurrence. We conclude that the division into core and satellite species is not a sample artefact but reflects different life history strategies. We also conclude that current models of niche division and co-occurrence might miss important aspects of community structure if they do not refer to patterns of dispersal. From these findings we infer that the regional distribution of core species might be shaped by species interactions and processes of niche divisions whereas the spatial distribution of satellite species are best interpreted as stemming from random dispersal. [source] Conflicts between traditional pastoralism and conservation of Himalayan ibex (Capra sibirica) in the Trans-Himalayan mountainsANIMAL CONSERVATION, Issue 2 2004Sumanta Bagchi There is recent evidence to suggest that domestic livestock deplete the density and diversity of wild herbivores in the cold deserts of the Trans-Himalaya by imposing resource limitations. To ascertain the degree and nature of threats faced by Himalayan ibex (Capra sibirica) from seven livestock species, we studied their resource use patterns over space, habitat and food dimensions in the pastures of Pin Valley National Park in the Spiti region of the Indian Himalaya. Species diet profiles were obtained by direct observations. We assessed the similarity in habitat use and diets of ibex and livestock using Non-Metric Multidimensional Scaling. We estimated the influence of the spatial distribution of livestock on habitat and diet choice of ibex by examining their co-occurrence patterns in cells overlaid on the pastures. The observed co-occurrence of ibex and livestock in cells was compared with null-models generated through Monte Carlo simulations. The results suggest that goats and sheep impose resource limitations on ibex and exclude them from certain pastures. In the remaining suitable habitat, ibex share forage with horses. Ibex remained relatively unaffected by other livestock such as yaks, donkeys and cattle. However, most livestock removed large amounts of forage from the pastures (nearly 250 kg of dry matter/day by certain species), thereby reducing forage availability for ibex. Pertinent conservation issues are discussed in the light of multiple-use of parks and current socio-economic transitions in the region, which call for integrating social and ecological feedback into management planning. [source] | ||||||||||