Species richness correlates of raw and standardized co‐occurrence metrics

Measuring β‐diversity and changes in species composition across multiple sites and environments is a major research focus in macroecology, and a variety of metrics have been proposed to quantify species co‐occurrence patterns in a species × site occurrence matrix. However, indices of β‐diversity and species co‐occurrence are often statistically dependent on the number of species in an assemblage. We compared the results of several common co‐occurrence metrics with patterns generated by a spatially explicit neutral model simulation. We found that all measures of co‐occurrence and β‐diversity, whether raw, rescaled or standardized by a null model expectation, were highly correlated with the total species richness of the landscape. The one important exception were the effect sizes of the fixed–fixed null model algorithm, which preserves row and column sums of the original matrix during matrix randomization. Our results call for a careful interpretation of meta‐analyses of assemblages that differ widely in species richness. At a minimum, observed species richness should be used as a statistical covariate in regression analyses, and results of the fixed–fixed algorithm should be compared carefully with the results of other randomization tests.     

Effects of an exotic invasive macrophyte (tropical signalgrass) on native plant community composition,species richness and functional diversity

1. The issue of freshwater species being threatened by invasion has become central in conservation biology because inland waters exhibit the highest species richness per unit area, but apparently have the highest extinctions rates on the planet. 2. In this article, we evaluated the effects of an exotic, invasive aquatic grass (Urochloa subquadripara– tropical signalgrass) on the diversity and assemblage composition of native macrophytes in four Neotropical water bodies (two reservoirs and two lakes). Species cover was assessed in quadrats, and plant biomass was measured in further quadrats, located in sites where tropical signalgrass dominated (D quadrats) and sites where it was not dominant or entirely absent (ND quadrats). The effects of tropical signalgrass on macrophyte species richness, Shannon diversity and number of macrophyte life forms (a surrogate of functional richness) were assessed through regressions, and composition was assessed with a DCA. The effects of tropical signalgrass biomass on the likelihood of occurrence of specific macrophyte life forms were assessed through logistic regression. 3. Tropical signalgrass had a negative effect on macrophyte richness and Shannon and functional diversity, and also influenced assemblage composition. Emergent, rooted with floating stems and rooted submersed species were negatively affected by tropical signalgrass, while the occurrence of free‐floating species was positively affected. 4. Our results suggest that competition with emergent species and reduction of underwater radiation, which reduces the number of submersed species, counteract facilitation of free‐floating species, contributing to a decrease in plant diversity. In addition, homogenisation of plant assemblages shows that tropical signalgrass reduces the beta diversity in the macrophyte community. 5. Although our results were obtained at fine spatial scales, they are cause for concern because macrophytes are an important part of freshwater diversity.     

Partitioning the diversity of riverine fish: the roles of habitat types and non-native species

1. Quantifying how biological diversity is distributed in the landscape is one of the central themes of conservation ecology. For this purpose, landscape classifications are being intensively used in conservation planning and biodiversity management, although there is still little information about their efficacy. 2. I used data from 158 running water sites in Hungary to examine the contribution of six a priori established habitat types to regional level diversity of fish assemblages. Three community measures [species richness, diversity (Shannon, Simpson indices), assemblage composition] were examined at two assemblage levels (entire assemblage, the native assemblage). The relative role of non‐native species was quantified to examine their contribution to patterns in diversity in this strongly human influenced landscape. 3. Additive diversity partitioning revealed the primary importance of beta diversity (i.e. among‐site factors) to patterns in species richness. Landscape‐scale patterns in species richness were best explained by between‐habitat type (beta₂: 41.2%), followed by within‐habitat type (beta₁: 37.7%) and finally within‐site (alpha: 21.1%) diversity. Diversity indices showed patterns different from species richness, indicating the importance of relative abundance distributions on the results. Exclusion of non‐natives from the analysis gave similar results to the entire‐assemblage level analysis. 4. Canonical analysis of principal coordinates, complemented with indicator species analysis justified the separation of fish assemblages among the habitat types, although classification error was high. Multivariate dispersion, a measure of compositional beta diversity, showed significant differences among the habitat types. Contrary to species diversity (i.e. richness, diversity indices), patterns in compositional diversity were strongly influenced by the exclusion of non‐natives from the analyses. 5. This study is the first to quantify how running water habitat types contribute to fish diversity at the landscape scale and how non‐native species influence this pattern. These results on riverine fish assemblages support the hypothesis that environmental variability (i.e. the diversity of habitat types) is an indication of biodiversity and can be used in large‐scale conservation designs. The study emphasises the joint application of additive diversity partitioning and multivariate statistics when exploring the contribution of landscape components to the overall biodiversity of the landscape mosaic.     

Species richness and structure of three Neotropical bat assemblages

We compared the assemblages of phyllostomid bats in three Neotropical rainforests with respect to species richness and assemblage structure and suggested a method to validate estimates of species richness for Neotropical bat assemblages based on mist-netting data. The fully inventoried bat assemblage at La Selva Biological Station (LS, 100 m elevation) in Costa Rica was used as a reference site to evaluate seven estimators of species richness. The Jackknife 2 method agreed best with the known bat species richness and thus was used to extrapolate species richness for an Amazonian bat assemblage (Tiputini Biodiversity Station; TBS, 200 m elevation) and an Andean premontane bat assemblage (Podocarpus National Park; BOM, 1000 m elevation) in Ecuador. Our results suggest that more than 100 bat species occur sympatrically at TBS and about 50 bat species coexist at BOM. TBS harbours one of the most species-rich bat assemblages known, including a highly diverse phyllostomid assemblage. Furthermore, we related assemblage structure to large-scale geographical patterns in floral diversity obtained from botanical literature. Assemblage structure of these three phyllostomid assemblages was influenced by differences in floral diversity at the three sites. At the Andean site, where understorey shrubs and epiphytes exhibit the highest diversity, the phyllostomid assemblage is mainly composed of understorey frugivores and nectarivorous species. By contrast, canopy frugivores are most abundant at the Amazonian site, coinciding with the high abundance of canopy fruiting trees. Assemblage patterns of other taxonomic groups also may reflect the geographical distribution patterns of floral elements in the Andean and Amazonian regions.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 617–629.     

Imprint of monsoonal patterns on the fish assemblage in coastal waters of south‐east India: a case study

The composition, species richness and diversity of a coastal fish assemblage from the Kalpakkam coast of south‐east India are described along with temporal distribution patterns related to seasonal fluctuations in dissolved oxygen, salinity, pH, chlorophyll‐a, phytoplankton and zooplankton species richness and density. A total of 244 fish species belonging to 21 orders, 87 families and 163 genera were recorded. The fish assemblage was dominated by reef‐associated species, followed by demersal species. The majority of the species (63%) are widely distributed in the western Indo‐Pacific as well as in the central Indo‐Pacific. Jaccard's coefficient analysis showed three distinct seasonal patterns of fish occurrence: pre‐monsoon (PrM), monsoon (M) and post‐monsoon (PoM). The maximum number of species was during the PrM period, followed by the PoM and M periods. Species occurrence analysis showed Sardinella longiceps to be dominant during PrM and M periods, Leiognathus dussumieri during the M period and Secutor insidiator and Secutor ruconius during the M and PoM periods. Canonical correspondence analysis indicated that salinity and rainfall were the two most influential environmental factors strongly correlated with temporal variation in the fish assemblage. The physico‐chemical conditions, in combination with factors such as greater food availability and shelter, might control the seasonal local distribution of the ichthyofauna in these Indian coastal waters.     

Differential resilience of invertebrates to fire

Fires are natural to ecosystems in many parts of the world, yet few studies have examined multi‐taxa invertebrate responses to these fires. We sampled a wide range of invertebrate taxa and feeding guilds at sites 3 months, 1 year and 3 years after fire, and in unburned control sites at the same time. A range of invertebrate sampling techniques was used on Table Mountain, in the Cape Floristic Region biodiversity hotspot, an area prone to natural and human‐induced fires. Sampling time differences strongly affected the composition of the whole assemblage, with fire having a major additional influence. Assemblages showed differential resilience to fire, especially in terms of species richness and abundance. One year after fire, the burned sites had the most compositional differences for the surface‐active species compared to control sites, while after 3 years, these sites were similar. Aerial assemblages were very different 3 years after burning, especially the pollination guild. Furthermore, these 3‐year‐old burned sites had the most unique species, suggesting that burning and longer‐term recovery is important for overall diversity. Some components of the invertebrate assemblage were remarkably resilient to fire (particularly ants), while others were far more conservative (pollinators). Nevertheless, fire allows new species to enter the ecosystem and can thus be used to promote local biodiversity if used appropriately. Ants alone should not be used to represent the whole invertebrate assemblage as they do not represent the more fire‐prone groups. A cross‐section of functional guilds is recommended in invertebrate recovery/fire management conservation programmes. These results have general significance in that a variety of feeding guilds need to be sampled when monitoring invertebrate responses to fire.     

The global distribution of frugivory in birds

Aim To examine patterns of avian frugivory across clades, geography and environments. Location Global, including all six major biogeographical realms (Afrotropics, Australasia, Indo‐Malaya, Nearctic, Neotropics and Palaearctic). Methods First, we examine the taxonomic distribution of avian frugivory within orders and families. Second we evaluate, with traditional and spatial regression approaches, the geographical patterns of frugivore species richness and proportion. Third, we test the potential of contemporary climate (water–energy, productivity, seasonality), habitat heterogeneity (topography, habitat diversity) and biogeographical history (captured by realm membership) to explain geographical patterns of avian frugivory. Results Most frugivorous birds (50%) are found within the perching birds (Passeriformes), but the woodpeckers and allies (Piciformes), parrots (Psittaciformes) and pigeons (Columbiformes) also contain a significant number of frugivorous species (9–15%). Frugivore richness is highest in the Neotropics, but peaks in overall bird diversity in the Himalayan foothills, the East African mountains and in some areas of Brazil and Bolivia are not reflected by frugivores. Current climate explains more variance in species richness and proportion of frugivores than of non‐frugivores whereas it is the opposite for habitat heterogeneity. Actual evapotranspiration (AET) emerges as the best single climatic predictor variable of avian frugivory. Significant differences in frugivore richness and proportion between select biogeographical regions remain after differences in environment (i.e. AET) are accounted for. Main conclusions We present evidence that both environmental and historical constraints influence global patterns of avian frugivory. Whereas water–energy dynamics possibly constrain frugivore distribution via indirect effects on food plants, regional differences in avian frugivory most likely reflect historical contingencies related to the evolutionary history of fleshy fruited plant taxa, niche conservatism and past climate change. Overall our results support an important role of co‐diversification and environmental constraints on regional assembly over macroevolutionary time‐scales.     

Bird dietary guild richness across latitudes,environments and biogeographic regions

Aim To integrate dietary knowledge and species distributions in order to examine the latitudinal, environmental, and biogeographical variation in the species richness of avian dietary guilds (herbivores, granivores, frugivores, nectarivores, aerial insectivores, terrestrial/arboreal insectivores, carnivores, scavengers, and omnivores). Location Global. Methods We used global breeding range maps and a comprehensive dietary database of all terrestrial bird species to calculate guild species richness for grid cells at 110 × 110 km resolution. We assessed congruence of guild species richness, quantified the steepness of latitudinal gradients and examined the covariation between species richness and climate, topography, habitat diversity and biogeographic history. We evaluated the potential of current environment and biogeographic history to explain global guild distribution and compare observed richness–environment relationships with those derived from random subsets of the global species pool. Results While most guilds (except herbivores and scavengers) showed strong congruence with overall bird richness, covariation in richness between guilds varied markedly. Guilds exhibited different peaks in species richness in geographical and multivariate environmental space, and observed richness–environment relationships mostly differed from random expectations. Latitudinal gradients in species richness were steepest for terrestrial/arboreal insectivores, intermediate for frugivores, granivores and carnivores, and shallower for all other guilds. Actual evapotranspiration emerged as the strongest climatic predictor for frugivores and insectivores, seasonality for nectarivores, and temperature for herbivores and scavengers (with opposite direction of temperature effect). Differences in species richness between biogeographic regions were strongest for frugivores and nectarivores and were evident for nectarivores, omnivores and scavengers when present‐day environment was statistically controlled for. Guild richness–environment relationships also varied between regions. Main conclusions Global associations of bird species richness with environmental and biogeographic variables show pronounced differences between guilds. Geographic patterns of bird diversity might thus result from several processes including evolutionary innovations in dietary preferences and environmental constraints on the distribution and diversification of food resources.     

Influence of late season fire on early successional vegetation of an Oklahoma prairie

Abstract. The study of vegetation dynamics in tallgrass prairie in response to fire has focused on dormant season fire in late successional prairies. Our objective was to determine if late season fire of varying frequency results in divergent successional patterns in an early successional tallgrass prairie disturbed by grazing and cultivation. Specifically, we evaluated the influence of late‐summer fires of varying frequency on community composition and species richness. We collected vegetation and environmental data on two sites burned in the late growing‐season at varying frequencies. These communities differed in composition depending primarily on edaphic factors, time since the last burn, and year‐to‐year variation. We interpret the time effect as related to changes in species composition accompanying plant succession that followed disturbance either from cropping and heavy grazing on the loamy site or heavy grazing on the shallow site. Other unidentified factors also have a role in vegetation dynamics on this prairie. Community composition and species richness were not consistently responsive to frequency of growing‐season fires.     

Importance of assemblage‐level thinning: A field experiment in an alpine meadow on the Tibet plateau

Question: Which fraction of the decrease in species richness under fertilization can be explained by assemblage‐level thinning? Location: An alpine meadow on the eastern Tibet plateau. Methods: 60‐m² plots were randomly assigned to a control or one of four levels of ammonium phosphate fertilizer. Treatments were repeated for three years. The effect of as semblage‐level thinning was decided based on similarity in quadrats within and between fertilizing levels, bootstrap simulation based on random thinning of the high density (low production, low fertility) quadrats and correlation of species’ biomass in low fertility and high fertility. Results: Fertilization increased production, reduced species richness and reduced density of individuals. Heavily fertilized quadrats are more similar in species composition in 2000 but less similar in 2001 and 2002. Rarefaction showed that a decrease in density can account for 32.3‐42.9% decrease of species richness, but the simulated species richness is always significantly higher than the observed one. When production and species richness are similar at two levels of fertilization, species biomass in the higher fertility treatment is positively correlated with biomass at lower fertility. When the two fertilizer levels differed in production and species richness, there was no evidence of correlation in species biomass, suggesting that assemblage level thinning cannot explain all the loss of species. Conclusion: Although a decrease in density could explain much of the decrease (up to 42.9%) in species richness when this alpine meadow was fertilized, other important mechanisms such as interspecific competition cannot be ignored. Future studies should investigate the effect of assemblage level thinning on species diversity, and search for mechanisms responsible for a decrease in diversity.     

Resilience of a high‐conservation‐value,semi‐arid grassland on fertile clay soils to burning,mowing and ploughing

In grassland reserves, managed disturbance is often necessary to maintain plant species diversity. We carried out experiments to determine the impact of fire, kangaroo grazing, mowing and disc ploughing on grassland species richness and composition in a nature reserve in semi‐arid eastern Australia. Vegetation response was influenced by winter–spring drought after establishment of the experiments, but moderate rainfall followed in late summer–autumn. Species composition varied greatly between sampling times, and the variability due to rainfall differences between seasons and years was greater than the effects of fire, kangaroo grazing, mowing or disc ploughing. In the fire experiment, species richness and composition recovered more rapidly after spring than autumn burning. Species richness and composition were similar to control sites within 12 months of burning and mowing, suggesting that removal of the dominant grass canopy is unnecessary to enhance plant diversity. Two fires (separated by 3 years) and post‐fire kangaroo grazing had only minor influence on species richness and composition. Even disc ploughing caused only a small reduction in native richness. The minor impact of ploughing was explained by the small areas that were ploughed, the once‐off nature of the treatment, and the high degree of natural movement and cracking in these shrink‐swell soils. Recovery of the composition and richness of these grasslands was rapid because of the high proportion of perennial species that resprout vegetatively after fire and mowing. There appears to be little conservation benefit from fire, mowing or ploughing ungrazed areas, as we could identify no native plant species dependent on frequent disturbance for persistence in this grassland community. However, the ability of the Astrebla‐ and Dichanthium‐dominated grasslands to recover quickly after disturbance, given favourable seasonal conditions, suggests that they are well adapted to natural disturbances (e.g. droughts, fire, flooding and native grazing).     

Response of plant species and life form diversity to variable fire histories and biomass in the jarrah forest of south‐west Australia

Frequent fires reduce the abundance of woody plant species and favour herbaceous species. Plant species richness also tends to increase with decreasing vegetation biomass and cover due to reduced competition for light. We assessed the influence of variable fire histories and site biomass on the following diversity measures: woody and herbaceous species richness, overall species richness and evenness, and life form evenness (i.e. the relative abundance or dominance among six herbaceous and six woody plant life forms), across 16 mixed jarrah (Eucalyptus marginata) and marri (Corymbia calophylla) forest stands in south‐west Australia. Fire frequency was defined as the total number of fires over a 30‐year period. Overall species richness and species evenness did not vary with fire frequency or biomass. However, there were more herbaceous species (particularly rushes, geophytes and herbs) where there were fewer shrubs and low biomass, suggesting that more herbaceous species coexist where dominance by shrubs is low. Frequently burnt plots also had lower number and abundance of shrub species. Life form evenness was also higher at both high fire frequency and low biomass sites. These results suggest that the impact of fire frequency and biomass on vegetation composition is mediated by local interactions among different life forms rather than among individual species. Our results demonstrate that measuring the variation in the relative diversity of different woody and herbaceous life forms is crucial to understanding the compositional response of forests and other structurally complex vegetation communities to changes in disturbance regime such as increased fire frequency.     

Conserving long unburnt vegetation is important for bird species,guilds and diversity

Landscape-level wildfires have a major role in structuring faunal assemblages, particularly in fire-prone landscapes. These effects are mediated by changes to vegetation structure and composition that directly influence the availability of shelter, feeding and breeding resources. We investigated the response of a semi-arid shrubland bird community in Western Australia to the prevailing fire regime by examining the abundance, diversity and guild structure in relation to time since fire. We also examined vegetation structural attributes in relation to time since fire. We surveyed 32 sites ranging in age from 12 to 84 years since last fire. A total of 845 birds from 40 species were recorded. Vegetation structure varied with fire history with old and very old sites characterised by less bare ground, more leaf litter cover and greater canopy cover. Bird community composition varied with time since fire, driven by increased bird species richness and abundance of insectivores, granivores/frugivores, golden whistlers, grey shrike-thrush and red-capped robins with time since fire. Frequent, intense landscape-scale fires transform the landscape into homogeneous young shrublands, which may render vegetation unsuitable for several species and guilds.     

Correlation of relative muzzle width and relative incisor width with dietary preference in ungulates

Qualitative observations suggest that grazing ungulates have relatively broader muzzles than browsing ones, and that grazers have incisors that are all of a similar size, as opposed to the large central and smaller lateral incisors seen in browsers. These differences may be correlated respectively with the need for grazing ungulates to maintain a large daily intake, or for browsing ungulates to forage selectively in a stand of vegetation. Quantitative examination of relative muzzle width and incisor width ratio in 95 species of living ungulates, correlated with seven different types of dietary preferences, substantiated these observations, although phylogenetic history may exhort a strong influence on morphological proportions. For example, equids have relatively narrower muzzles than grazing ruminants despite their less selective mode of feeding. The narrowest relative muzzle widths are not found in regular browsers, but in high level browsers and in mixed feeders in open habitats. Incisor width ratio can distinguish grazers from browsers, but can not be used to discriminate mixed feeders from other feeding types, and grazers appear to have incisors that are relatively broader overall than those of other dietary types, in correlation with their relatively broader muzzles.     

Wildfire severity reduces richness and alters composition of soil fungal communities in boreal forests of western Canada

Wildfire is the dominant disturbance in boreal forests and fire activity is increasing in these regions. Soil fungal communities are important for plant growth and nutrient cycling postfire but there is little understanding of how fires impact fungal communities across landscapes, fire severity gradients, and stand types in boreal forests. Understanding relationships between fungal community composition, particularly mycorrhizas, and understory plant composition is therefore important in predicting how future fire regimes may affect vegetation. We used an extreme wildfire event in boreal forests of Canada's Northwest Territories to test drivers of fungal communities and assess relationships with plant communities. We sampled soils from 39 plots 1 year after fire and 8 unburned plots. High‐throughput sequencing (MiSeq, ITS) revealed 2,034 fungal operational taxonomic units. We found soil pH and fire severity (proportion soil organic layer combusted), and interactions between these drivers were important for fungal community structure (composition, richness, diversity, functional groups). Where fire severity was low, samples with low pH had higher total fungal, mycorrhizal, and saprotroph richness compared to where severity was high. Increased fire severity caused declines in richness of total fungi, mycorrhizas, and saprotrophs, and declines in diversity of total fungi and mycorrhizas. The importance of stand age (a surrogate for fire return interval) for fungal composition suggests we could detect long‐term successional patterns even after fire. Mycorrhizal and plant community composition, richness, and diversity were weakly but significantly correlated. These weak relationships and the distribution of fungi across plots suggest that the underlying driver of fungal community structure is pH, which is modified by fire severity. This study shows the importance of edaphic factors in determining fungal community structure at large scales, but suggests these patterns are mediated by interactions between fire and forest stand composition.     

Environmental drivers of ant species richness and composition across the Argentine Pampas grassland

Understanding the underlying mechanisms causing diversity patterns is a fundamental objective in ecology and science‐based conservation biology. Energy and environmental‐heterogeneity hypotheses have been suggested to explain spatial changes in ant diversity. However, the relative roles of each one in determining alpha and beta diversity patterns remain elusive. We investigated the main factors driving spatial changes in ant (Hymenoptera, Formicidae) species richness and composition (including turnover and nestedness components) along a 500 km longitudinal gradient in the Pampean region of Argentina. Ants were sampled using pitfall traps in 12 sample sites during the summer. We performed a model selection approach to analyse responses of ant richness and composition dissimilarity to environmental factors. Then, we computed a dissimilarity partitioning of the contributions of spatial turnover and nestedness to total composition dissimilarity. Temporal habitat heterogeneity and temperature were the primary factors explaining spatial patterns of epigean ant species richness across the Pampas. The distance decay in species composition similarity was best accounted by temperature dissimilarity, and turnover had the greatest contribution to the observed beta diversity pattern. Our findings suggest that both energy and environmental‐heterogeneity‐related variables are key factors shaping richness patterns of ants and niche‐based processes instead of neutral processes appear to be regulating species composition of ant assemblages. The major contribution of turnover to the beta diversity pattern indicated that lands for potential reconversion to grassland should represent the complete environmental gradient of the Pampean region, instead of prioritizing a single site with high species richness.     

Fire Season and Dominance in an Illinois Tallgrass Prairie Restoration

North American prairie remnants and restorations are normally managed with dormant‐season prescribed fires. Growing‐season fire is of interest because it suppresses dominant late‐flowering grasses and forbs, thereby making available light and other resources used by subdominant grasses and forbs that comprise most prairie diversity. Here we report a twofold increase in mean frequency and richness of subdominant species after late‐summer fire. Stimulation of subdominants was indiscriminate; richness of prairie and volunteer species increased in species that flowered in early, mid‐, or late season. Early spring fire, the management tool used on this site until this experiment, had no effect on subdominant richness or frequency. Neither burn treatment affected reproductive tillering of the tallgrasses Sorghastrum nutans or Panicum virgatum. Flowering of Andropogon gerardii increased 4‐fold after early‐spring fires and 11‐fold after late‐summer fires. These preliminary results suggest that frequency and species richness of subdominants can be improved by late growing‐season fire without compromising vigor of warm‐season tallgrasses.     

Effects of fire regime on plant species richness and composition differ among forest,woodland and heath vegetation

Question

Do the effects of fire regimes on plant species richness and composition differ among floristically similar vegetation types?

Location

Booderee National Park, south‐eastern Australia.

Methods

We completed floristic surveys of 87 sites in Sydney Coastal dry sclerophyll vegetation, where fire history records have been maintained for over 55 years. We tested for associations between different aspects of the recent fire history and plant species richness and composition, and whether these relationships were consistent among structurally defined forest, woodland and heath vegetation types.

Results

The relationship between fire regime variables and plant species richness and composition differed among vegetation types, despite the three vegetation types having similar species pools. Fire frequency was positively related to species richness in woodland, negatively related to species richness in heath, and unrelated to species richness in forest. These different relationships were explained by differences in the associations between fire history and species traits among vegetation types. The negative relationship between fire frequency and species richness in heath vegetation was underpinned by reduced occurrence of resprouting species at high fire frequency sites (more than four fires in 55 years). However, in forest and woodland vegetation, resprouting species were not negatively associated with fire frequency.

Conclusions

We hypothesize that differing relationships among vegetation types were underpinned by differences in fire behaviour, and/or biotic and abiotic conditions, leading to differences in plant species mortality and post‐fire recovery among vegetation types. Our findings suggest that even when there is a high proportion of shared species between vegetation types, fires can have very different effects on vegetation communities, depending on the structural vegetation type. Both research and management of fire regimes may therefore benefit from considering vegetation types as separate management units.     

Environmental drivers of beta-diversity patterns in New-World birds and mammals

Current macroecological research places great emphasis on patterns of species richness (alpha diversity) and the underlying ecological and evolutionary processes involved in their origin and maintenance. However, few studies dealing with continental scales have addressed dissimilarities in species composition among areas (beta diversity). Using data for the occurrence of 3836 bird and 1641 mammal species in 4220 cells covering the New World, we assessed whether broad-scale macroecological patterns in beta diversity are related to dissimilarities in environmental variables and biotic units. We employed spatial regression and tree regression to model beta diversity. Difference in altitude was the best predictor of beta diversity. Accordingly, the highest beta diversity values were found in mountainous areas, particularly in the Andes, Central America and western North America. Explanatory variables related to transitions between biotic units (biome, ecoregion) were relatively unimportant. Areas that differ in altitude from their surroundings harbor different sets of species, and this may reflect either species adaptation to particular environmental conditions by range shifts, or species divergence by vicariance, or both.     

Tooth wear in captive wild ruminant species differs from that of free-ranging conspecifics

The mesowear method evaluates the wear patterns of herbivore cheek teeth by visually evaluating the facet development of the occlusal surfaces. It thus allows classification of most herbivorous ungulates into browsers, grazers or intermediate feeders, due to the fact that in grazers, tooth wear is characterized by a comparatively high degree of abrasion, most probably due to the presence of silicacious phytoliths in grasses, a higher amount of dust and grit adhering to their forage, or both. It has been suggested that excessive tooth wear could be a particularly limiting factor in the husbandry of captive large browsing species, and major tooth wear was demonstrated in captive as compared to free-ranging giraffe. If this increased tooth wear in captivity was an effect of feeding type and diets fed, then it would be expected that other browsing species are affected in a similar manner. In order to test this hypothesis, we investigated the dental mesowear pattern in captive individuals of 19 ruminant species and compared the results to data on free-ranging animals. Compared to free-ranging populations, captive browsers show a significantly more abrasion-dominated tooth wear signal. The reverse applies to captive grazers, which tend to show a less abrasion-dominated wear in captivity. Captive ruminants were generally more homogenous in their wear signature than free-ranging ruminants. If grit contamination in the natural habitat is a major cause of dental wear in grazers, then diets in captivity, although similar in botanical composition, most likely contain less abrasives due to feeding hygiene. If dental wear is one of the major factors limiting longevity, then captive grazers should achieve longer lifespans than both captive browsers and free-ranging grazers. In particular with respect to browsers, the results suggest that captive feeding regimes could be improved.