Ecological disturbance is fundamental to the dynamics of biological communities, yet a conceptual framework for understanding the responses of faunal communities to disturbance remains elusive. Here, ...I propose five principles for understanding the disturbance dynamics of ants—a globally dominant faunal group that is widely used as bioindicators in land management, which appear to have wide applicability to other taxa.
These principles are as follows: (1) The most important effects of habitat disturbance on ants are typically indirect, through its effects on habitat structure, microclimate, resource availability and competitive interactions; (2) habitat openness is a key driver of variation in ant communities; (3) ant species responses to disturbance are to a large degree determined by their responses to habitat openness; (4) the same disturbance will have different effects on ants in different habitats, because of different impacts on habitat openness; and (5) ant community responses to the same disturbance will vary according to ant functional composition and biogeographical history in relation to habitat openness.
I illustrate these principles using results primarily from studies of ant responses to fire, a dominant agent of disturbance globally, to provide a common disturbance currency for comparative analysis.
I argue that many of the principles also apply to other faunal groups and so can be considered as general ecological “laws.” As is the case for ants, many impacts of habitat disturbance on other faunal groups are fundamentally related to habitat openness, the effects of disturbance on it and the functional composition of species in relation to it.
This article provides a novel conceptual framework for a predictive understanding of the disturbance dynamics of ants, a globally dominant faunal group. The framework is based on five principles that appear to be widely applicable to fauna in general and therefore qualify as general ecological “laws.”
Aim
Fire is particularly frequent, complex and contentious in the vast tropical savannas of northern Australia, where declines in many threatened species are associated with fire, and substantial ...areas are under fire management for greenhouse gas abatement. Controlled field experiments are crucial for understanding biodiversity responses, and here I present key insights into faunal responses to fire that have been revealed by them, along with their lessons for fire management.
Location
Australian monsoonal tropics.
Methods
Results are synthesized from six replicated fire experiments that have been conducted in Australian savannas and include multispecies assessments of fauna. The synthesis also draws on other fire studies and is presented in the form of five key insights into faunal responses.
Results
The key insights are as follows: (a) most faunal groups are extremely resilient to fire, with highly contrasting fire regimes often having little or no detectable impact on species abundances, at least in the medium term; (b) the most important effects of fire are typically indirect through habitat modification, even when there is substantial direct mortality; (c) fire intensity is not as important a factor as is widely thought; rather, fire frequency is particularly important; (d) there will always be winners and losers with any fire; and (e) fire is required for the maintenance of diversity.
Main conclusions
These insights have important implications for conservation management in Australian savannas: management needs to focus on fire‐induced changes to habitat suitability, and to consider faunal outcomes at the landscape scale; a combination of frequently (every 2–3 years) and less frequently (every ≥5 years) burned habitat may adequately conserve the great majority of animal species without a need for complex fire mosaics; special management attention is required for frequent‐fire losers because of an extremely low representation of longer‐unburnt habitat; and fire needs to be actively managed to promote diversity, not excluded. The insights are widely applicable to tropical grassy ecosystems more generally, and some appear to be universal to fire‐prone biomes.
•Tropical grassy biomes are extensive and critical to human livelihoods.•The definition of these grassy systems is inconsistent and misleading.•We discuss novel threats linked to problems with biome ...definition.•The assumption that ‘more trees are better’ does not hold for tropical grassy biomes.
Tropical grassy biomes (TGBs) are globally extensive, provide critical ecosystem services, and influence the earth–atmosphere system. Yet, globally applied biome definitions ignore vegetation characteristics that are critical to their functioning and evolutionary history. Hence, TGB identification is inconsistent and misinterprets the ecological processes governing vegetation structure, with cascading negative consequences for biodiversity. Here, we discuss threats linked to the definition of TGB, the Clean Development Mechanism (CDM) and Reducing Emissions from Deforestation and Forest Degradation schemes (REDD+), and enhanced atmospheric CO2, which may facilitate future state shifts. TGB degradation is insidious and less visible than in forested biomes. With human reliance on TGBs and their propensity for woody change, ecology and evolutionary history are fundamental to not only the identification of TGBs, but also their management for future persistence.
The herbaceous layer is the dominant fuel for fire in tropical savannas, the world's most fire‐prone biome. However, little is known about variation in flammability among different growth forms, as ...well as how flammability varies seasonally. Here, we describe such variation in Brazilian Cerrado, the world's most phytodiverse tropical savanna. We measured three components of flammability (maximum burning temperature, burning rate, and burnt biomass) and morphophysiological traits (dead biomass percentage, moisture content, and specific leaf area) of five species of each of grasses, forbs, and shrubs throughout the wet and dry season. We found that grasses were the most flammable growth form and that their flammability was highest in the middle of the dry season when the percentage of dead biomass was highest (60%), and moisture content was low (25%). Flammability did not vary across seasons for either forbs or shrubs. Dead biomass, moisture content, and specific leaf area were all strongly correlated with flammability. These findings explain the dominant role played by grasses as drivers of flammability in tropical savannas, and they improve our understanding of how savanna flammability varies across space and time depending on the composition of the grass layer and its level of seasonal curing. This enables a better prediction of fire spread and behavior in different savanna types based on grass‐layer composition.
Grasses are the most flammable growth form and their flammability vary between wet and dry season. Shrubs and forbs does not vary their flammability across seasons. Such findings explain the dominant role played by grasses and how savanna flammability vary across space and time.
The underestimated biodiversity of tropical grassy biomes Murphy, Brett P.; Andersen, Alan N.; Parr, Catherine L.
Philosophical transactions - Royal Society. Biological sciences,
09/2016, Letnik:
371, Številka:
1703
Journal Article
Recenzirano
Odprti dostop
For decades, there has been enormous scientific interest in tropical savannahs and grasslands, fuelled by the recognition that they are a dynamic and potentially unstable biome, requiring periodic ...disturbance for their maintenance. However, that scientific interest has not translated into widespread appreciation of, and concern about threats to, their biodiversity. In terms of biodiversity, grassy biomes are considered poor cousins of the other dominant biome of the tropics—forests. Simple notions of grassy biomes being species-poor cannot be supported; for some key taxa, such as vascular plants, this may be valid, but for others it is not. Here, we use an analysis of existing data to demonstrate that high-rainfall tropical grassy biomes (TGBs) have vertebrate species richness comparable with that of forests, despite having lower plant diversity. The Neotropics stand out in terms of both overall vertebrate species richness and number of range-restricted vertebrate species in TGBs. Given high rates of land-cover conversion in Neotropical grassy biomes, they should be a high priority for conservation and greater inclusion in protected areas. Fire needs to be actively maintained in these systems, and in many cases re-introduced after decades of inappropriate fire exclusion. The relative intactness of TGBs in Africa and Australia make them the least vulnerable to biodiversity loss in the immediate future. We argue that, like forests, TGBs should be recognized as a critical—but increasingly threatened—store of global biodiversity.
This article is part of the themed issue ‘Tropical grassy biomes: linking ecology, human use and conservation’.
Quantifying and understanding the main drivers of biodiversity responses to human disturbances at multiple scales is key to foster effective conservation plans and management systems. Here we report ...on a detailed regional assessment of the response of ant communities to land-use change and forest disturbance in the Brazilian Amazon. We aimed to explore the effects of land-use intensification at both site and landscape scales, examining variation in ant species richness and composition, and asking which set of environmental variables best predict observed patterns of diversity. We sampled 192 sites distributed across 18 landscapes (each 50km2) in Paragominas, eastern Brazilian Amazon, covering ca. 20,000km2. We sampled from undisturbed primary forest through varyingly disturbed primary forests, secondary forests, pastures and mechanised agriculture, following a gradient of decreasing total aboveground biomass. Irrespective of forest disturbance class, ant species richness was almost twice as high in forests when compared to production areas. In contrast, ant species composition showed continuous variation from primary forest to intensive agriculture, following a gradient of aboveground biomass. Ant species richness at all spatial scales increased with primary forest cover in the surrounding landscapes. We highlight the limited value of species richness as an indicator of changes in habitat quality, reinforcing calls to consider species composition in assessments of forest disturbance. Taken together, our results reveal the unique biodiversity value of undisturbed primary forests, but also show that disturbed primary forests and secondary forests have high conservation value, and thus play an important role in regional conservation planning.
•Ants were sampled over multiple landscapes and land-uses at a deforestation frontier.•Forest areas supported almost twice as many species as production areas.•Total landscape richness increases with the proportion of remaining primary forest.•Species composition varied consistently across a gradient of aboveground biomass.•Disturbed forests have an impoverished ant fauna but remain vital for conservation.
Fire is a powerful tool for conservation management at a landscape scale, but a rigorous evidence base is often lacking for understanding its impacts on biodiversity in different biomes. Fire-induced ...changes to habitat openness have been identified as an underlying driver of responses of faunal communities, including for ants. However, most studies of the impacts of fire on ant communities consider only epigeic (foraging on the soil surface) species, which may not reflect the responses of species inhabiting other vertical strata. Here, we examine how the responses of ant communities vary among vertical strata in a highly fire-prone biome. We use a long-term field experiment to quantify the effects of fire on the abundance, richness, and composition of ant assemblages of four vertical strata (subterranean, leaf litter, epigeic, and arboreal) in an Australian tropical savanna. We first document the extent to which each stratum harbors distinct assemblages. We then assess how the assemblage of each stratum responds to three fire-related predictors: fire frequency, fire activity, and vegetation cover. Each stratum harbored a distinct ant assemblage and showed different responses to fire. Leaf litter and epigeic ants were most sensitive to fire because it directly affects their microhabitats, but they showed contrasting negative and positive responses, respectively. Subterranean ants were the least sensitive because of the insulating effects of soil. Our results show that co-occurring species of the same taxonomic group differ in the strength and direction of their response to fire depending on the stratum they inhabit. As such, effective fire management for biodiversity conservation should consider species in all vertical strata.Fire is a powerful tool for conservation management at a landscape scale, but a rigorous evidence base is often lacking for understanding its impacts on biodiversity in different biomes. Fire-induced changes to habitat openness have been identified as an underlying driver of responses of faunal communities, including for ants. However, most studies of the impacts of fire on ant communities consider only epigeic (foraging on the soil surface) species, which may not reflect the responses of species inhabiting other vertical strata. Here, we examine how the responses of ant communities vary among vertical strata in a highly fire-prone biome. We use a long-term field experiment to quantify the effects of fire on the abundance, richness, and composition of ant assemblages of four vertical strata (subterranean, leaf litter, epigeic, and arboreal) in an Australian tropical savanna. We first document the extent to which each stratum harbors distinct assemblages. We then assess how the assemblage of each stratum responds to three fire-related predictors: fire frequency, fire activity, and vegetation cover. Each stratum harbored a distinct ant assemblage and showed different responses to fire. Leaf litter and epigeic ants were most sensitive to fire because it directly affects their microhabitats, but they showed contrasting negative and positive responses, respectively. Subterranean ants were the least sensitive because of the insulating effects of soil. Our results show that co-occurring species of the same taxonomic group differ in the strength and direction of their response to fire depending on the stratum they inhabit. As such, effective fire management for biodiversity conservation should consider species in all vertical strata.
Most comparative studies of biological communities in different biogeographical regions highlight ecological convergence under matched environments. Here we use savanna ant communities as a striking ...example where such convergence has not occurred. The savanna ant faunas of Australia, Brazil and Africa have very different functional composition due to their highly contrasting evolutionary origins.We synthesise the literature relating to the diversity and composition of savanna ant communities in the three continents, along with ant community responses to fire and aridity.Australian savannas evolved in association with a desert biome and its fauna is strongly arid adapted: it is exceptionally thermophilic, granivorous species are extremely diverse and abundant, high diversity is maintained with increasing aridity, and communities are highly resilient to simplification of vegetation structure induced by frequent fire. Brazilian savannas evolved surrounded by rainforest and have a forest‐derived ant fauna; this fauna is not so highly thermophilic, granivory is almost absent, diversity declines with increasing aridity and communities are highly sensitive to fire‐induced vegetation change. Africa has a very generalised ant fauna that has moderate representations of highly thermophilic and granivorous species, diversity appears to decline with increasing aridity, but communities are highly resilient to fire.The different biogeographical histories of tropical savannas in Australia, Brazil and Africa have led to functionally distinct ant faunas that display contrasting responses to environmental stress and disturbance. Phylogenetic niche conservatism seems to be particularly strong for granivory and thermophilia. Such intercontinental differences have important implications for understanding biodiversity responses to land management and climate change.
We introduce the concept of Biome Awareness Disparity (BAD)—defined as a failure to appreciate the significance of all biomes in conservation and restoration policy—and quantify disparities in (a) ...attention and interest, (b) action and (c) knowledge among biomes in tropical restoration science, practice and policy.
By analysing 50,000 tweets from all Partner Institutions of the UN Decade of Ecosystem Restoration, and 45,000 tweets from the main science and environmental news media world‐wide, we found strong disparities in attention and interest relative to biome extent and diversity. Tweets largely focused on forests, whereas open biomes (such as grasslands, savannas and shrublands) received less attention in relation to their area. In contrast to these differences in attention, there were equivalent likes and retweets between forest versus open biomes, suggesting the disparities may not reflect the views of the general public.
Through a literature review, we found that restoration experiments are disproportionately concentrated in rainforests, dry forests and mangroves. More than half of the studies conducted in open biomes reported tree planting as the main restoration action, suggesting inappropriate application of forest‐oriented techniques.
Policy implications. We urge scientists, policymakers and land managers to recognise the value of open biomes for protecting biodiversity, securing ecosystem services, mitigating climate change and enhancing human livelihoods. Fixing Biome Awareness Disparity will increase the likelihood of the United Nations Decade on Ecosystem Restoration successfully delivering its promises.
Resumo
Nós introduzimos o conceito de disparidade de consciência de bioma (DCS)—definido como uma falha em reconhecer a importância de todos os biomas na política de conservação e restauração— e quantificamos disparidades em (i) atenção e interesse, (ii) ação, e (iii) conhecimento na ciência, prática e política de restauração de biomas tropicais.
Analisamos mais de 50,000 tweets de todas as instituições parceiras da Década das Nações Unidas para a Restauração de Ecossistemas, e mais de 45,000 tweets dos maiores canais de mídia de ciência e meio ambiente em todo mundo e encontramos fortes disparidades de atenção e interesse relativos à extensão e diversidade de biomas. Tweets focaram fortemente em florestas, enquanto biomas abertos (como campos, savanas e arbustais), receberam menor atenção relativo à sua área. Em contraste com as disparidades em atenção, encontramos um número equivalente de curtidas e retweets entre biomas florestais e biomas abertos, sugerindo que as disparidades não refletem a visão do público em geral.
Nossa revisão de literatura demonstrou que os experimentos de restauração se concentraram desproporcionalmente em florestas úmidas, secas e manguezais. Mais da metade dos estudos conduzidos em biomas abertos reportou o plantio de árvores como a principal ação de restauração, sugerindo a aplicação incorreta de técnicas centradas em florestas.
Convidamos os cientistas, formuladores de políticas públicas e gestores ambientais a reconhecer o valor dos biomas abertos para proteção da biodiversidade, garantia de serviços ecossistêmicos, mitigação das mudanças climáticas, e melhoria dos meios de subsistência humana. Reparar a Disparidade de Consciência de Bioma aumentará a probabilidade de a Década das Nações Unidas para a Restauração de Ecossistemas cumprir com sucesso suas promessas.
We urge scientists, policymakers and land managers to recognise the value of open biomes for protecting biodiversity, securing ecosystem services, mitigating climate change and enhancing human livelihoods. Fixing Biome Awareness Disparity will increase the likelihood of the United Nations Decade on Ecosystem Restoration successfully delivering its promises.
Ants are a ubiquitous, highly diverse, and ecologically dominant faunal group. They represent a large proportion of global terrestrial faunal biomass and play key ecological roles as soil engineers, ...predators, and re-cyclers of nutrients. They have particularly important interactions with plants as defenders against herbivores, as seed dispersers, and as seed predators. One downside to the ecological importance of ants is that they feature on the list of the world’s worst invasive species. Ants have also been important for science as model organisms for studies of diversity, biogeography, and community ecology. Despite such importance, ants remain remarkably understudied. A large proportion of species are undescribed, the biogeographic histories of most taxa remain poorly known, and we have a limited understanding of spatial patterns of diversity and composition, along with the processes driving them. The papers in this Special Issue collectively address many of the most pressing questions relating to ant diversity. What is the level of ant diversity? What is the origin of this diversity, and how is it distributed at different spatial scales? What are the roles of niche partitioning and competition as regulators of local diversity? How do ants affect the ecosystems within which they occur? The answers to these questions provide valuable insights not just for ants, but for biodiversity more generally.
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