Animal species diversity driven by habitat heterogeneity/diversity: the importance of keystone structures

Aim In a selected literature survey we reviewed studies on the habitat heterogeneity–animal species diversity relationship and evaluated whether there are uncertainties and biases in its empirical support. Location World-wide. Methods We reviewed 85 publications for the period 1960–2003. We screened each publication for terms that were used to define habitat heterogeneity, the animal species group and ecosystem studied, the definition of the structural variable, the measurement of vegetation structure and the temporal and spatial scale of the study. Main conclusions The majority of studies found a positive correlation between habitat heterogeneity/diversity and animal species diversity. However, empirical support for this relationship is drastically biased towards studies of vertebrates and habitats under anthropogenic influence. In this paper, we show that ecological effects of habitat heterogeneity may vary considerably between species groups depending on whether structural attributes are perceived as heterogeneity or fragmentation. Possible effects may also vary relative to the structural variable measured. Based upon this, we introduce a classification framework that may be used for across-studies comparisons. Moreover, the effect of habitat heterogeneity for one species group may differ in relation to the spatial scale. In several studies, however, different species groups are closely linked to ‘keystone structures’ that determine animal species diversity by their presence. Detecting crucial keystone structures of the vegetation has profound implications for nature conservation and biodiversity management.     

Restoration for variability: emergence of the habitat diversity paradigm in terrestrial ecosystem restoration

Ecosystem restoration implies focusing on multiple trophic levels and ecosystem functioning, yet higher trophic levels, that is, animals, are less frequently targeted by restoration than plants. Habitat diversity, the spatial heterogeneity between and within habitat patches in a landscape, is a well‐known driver of species diversity, and offers possible ways to increase species diversity at multiple trophic levels. We argue that habitat diversity is central in whole‐ecosystem restoration as we review its importance, provide a practical definition for its components, and propose ways to target it in restoration. Restoration targeting habitat diversity is used commonly in aquatic ecosystems, mostly to increase the physical diversity of habitats, meant to provide more niches available to a higher number of animal species. To facilitate the uptake of habitat diversity in terrestrial ecosystem restoration, we distinguish between compositional and structural habitat diversity, because different animal groups will respond to different aspects of habitat diversity. We also propose four methods to increase habitat diversity: varying the starting conditions to obtain divergent successional pathways, emulating natural disturbances, establishing keystone structures, and applying ecosystem engineer species. We provide two case studies to illustrate how these components and methods can be incorporated in restoration. We conclude that targeting habitat diversity is a promising way to restore habitats for a multitude of species of animals and plants, and that it should become mainstream in restoration ecology and practice. We encourage the restoration community to consider compositional and structural habitat diversity and to specifically target habitat diversity in ecosystem restoration.     

Disentangling vegetation diversity from climate–energy and habitat heterogeneity for explaining animal geographic patterns

Broad‐scale animal diversity patterns have been traditionally explained by hypotheses focused on climate–energy and habitat heterogeneity, without considering the direct influence of vegetation structure and composition. However, integrating these factors when considering plant–animal correlates still poses a major challenge because plant communities are controlled by abiotic factors that may, at the same time, influence animal distributions. By testing whether the number and variation of plant community types in Europe explain country‐level diversity in six animal groups, we propose a conceptual framework in which vegetation diversity represents a bridge between abiotic factors and animal diversity. We show that vegetation diversity explains variation in animal richness not accounted for by altitudinal range or potential evapotranspiration, being the best predictor for butterflies, beetles, and amphibians. Moreover, the dissimilarity of plant community types explains the highest proportion of variation in animal assemblages across the studied regions, an effect that outperforms the effect of climate and their shared contribution with pure spatial variation. Our results at the country level suggest that vegetation diversity, as estimated from broad‐scale classifications of plant communities, may contribute to our understanding of animal richness and may be disentangled, at least to a degree, from climate–energy and abiotic habitat heterogeneity.     

Environmental change and predator diversity drive alpha and beta diversity in freshwater macro and microorganisms

Global biodiversity is eroding due to anthropogenic causes, such as climate change, habitat loss, and trophic simplification of biological communities. Most studies address only isolated causes within a single group of organisms; however, biological groups of different trophic levels may respond in particular ways to different environmental impacts. Our study used natural microcosms to investigate the predicted individual and interactive effects of warming, changes in top predator diversity, and habitat size on the alpha and beta diversity of macrofauna, microfauna, and bacteria. Alpha diversity (i.e., richness within each bromeliad) generally explained a larger proportion of the gamma diversity (partitioned in alpha and beta diversity). Overall, dissimilarity between communities occurred due to species turnover and not species loss (nestedness). Nevertheless, the three biological groups responded differently to each environmental stressor. Microfauna were the most sensitive group, with alpha and beta diversity being affected by environmental changes (warming and habitat size) and trophic structure (diversity of top predators). Macrofauna alpha and beta diversity was sensitive to changes in predator diversity and habitat size, but not warming. In contrast, the bacterial community was not influenced by the treatments. The community of each biological group was not mutually concordant with the environmental and trophic changes. Our results demonstrate that distinct anthropogenic impacts differentially affect the components of macro and microorganism diversity through direct and indirect effects (i.e., bottom‐up and top‐down effects). Therefore, a multitrophic and multispecies approach is necessary to assess the effects of different anthropogenic impacts on biodiversity.     

Heterogeneous flows foster heterogeneous assemblages: relationships between functional diversity and hydrological heterogeneity in riparian plant communities

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Distinguishing area and habitat heterogeneity effects: a simulation test of the MacNally and Watson (1997) protocol

Distinguishing the roles that different factors, such as sampling effects and habitat heterogeneity, play in generating species‐area curves continues to be difficult in many communities. A recent response to this challenge is the proposal of a ‘zoom’ protocol in which species richness and habitat heterogeneity are sampled in successively larger units (transects or quadrats). The utility of this approach requires that there be justifiable, predictable and unambiguous relationships between richness and heterogeneity. Results of computer simulations that I have done to test the predicted relationships demonstrate, however, that the predicted patterns were not always observed and, on occasion, more complex relationships were observed in their place. While the development of such protocols may increase our understanding of species‐area curves, they are unlikely ever to pronounce unambiguously on their causes.     

Mammalian beta diversity in the Great Basin, western USA: palaeontological data suggest deep origin of modern macroecological structure

Aim Recent work indicates that desert assemblages have elevated beta (β) diversity (between‐locality turnover of species composition). This study compares β diversities between the Great Basin and the Great Plains of the western USA over the last 17 Myr. Today, the Great Basin is a topographically diverse desert scrubland to woodland and the Great Plains are low‐relief temperate grassland, but 17 Ma they were more similar in topography, climate and land cover. A georeferenced database of mammal occurrences, complied from several sources, is used to test two hypotheses for the elevation of Great Basin β diversity: (1) that tectonic change of the topography has driven increased habitat packing in high‐ and low‐elevation habitats, and (2) that climatic cycling in the Pleistocene has driven faunas from neighbouring provinces to overlap in the region. Location The Great Basin of the USA, centred on Nevada, and the central Great Plains of the USA, centred on Nebraska. Methods Mammalian faunal lists compiled from published records and the records of many museums, available online, were partitioned into time‐slices ranging from the recent to 17 Myr old. Beta diversity was calculated for each time‐slice in two ways: multiplicative β diversity using first‐order jackknife richness, and additive beta diversity using Simpson's evenness. Results Beta diversity is elevated in Nevada relative to Nebraska today. Beta diversity has been higher in the Great Basin since the Pleistocene and possibly since the late Early Hemphillian (c. 7 Ma). Beta diversity in the Late Barstovian (c. 13.5 Ma) of the Great Plains was higher even than β diversity in the Great Basin of today. Main conclusions The elevated β diversity in the Hemphillian supports the tectonic change hypothesis. The patterns of β diversity in the Recent, Pleistocene and Hemphillian all suggest that local‐scale processes are important. The β diversity of the Late Barstovian Great Plains supports other studies indicating increased primary productivity or species packing.     

Functional and phylogenetic diversity of an agricultural matrix avifauna: The role of habitat heterogeneity in Afrotropical farmland

Varied strategies to alleviate the loss of farmland biodiversity have been tested, yet there is still insufficient evidence supporting their effectiveness, especially when considering phylogenetic and functional diversity alongside traditional taxonomic diversity metrics. This conservation challenge is accentuated in the Afrotropics by the rapid agricultural expansion and intensification for the production of cash crops and by a comparative lack of research. In this study, we assessed how farming practices influence avian phylogenetic and functional diversity. We conducted point‐count surveys to assess avian diversity in monocultures of tea and mixed crop farming systems surrounding the Nyungwe rainforest in south‐west Rwanda, allowing us to investigate the drivers of avian diversity at farm level. Species composition was found to be moderately different between farm types, with mixed crop farms supporting higher phylogenetic diversity than tea plantations. There were no significant seasonal differences in species composition, functional or phylogenetic diversity. Overall, functional diversity did not differ between farm types, but the dispersion of trophic‐related traits was significantly higher in mixed crop farms. Both functional and phylogenetic diversity were influenced by floristic diversity, vegetation height, tree number, and elevation to varying degrees. Our results also (i) highlight the role of farmland heterogeneity (e.g., crop species composition, height, and tree cover extent) in encouraging avian functional and phylogenetic diversity in the Afrotropics and (ii) indicate that the generally negative biodiversity impacts of monoculture agriculture can be partially alleviated by extensive agroforestry with an emphasis on indigenous tree species.     

Interactions between soil heterogeneity and freezing: Implications for grassland plant diversity and relative species abundances

Plant stress resulting from soil freezing is expected to increase in northern temperate regions over the next century due to reductions in snow cover caused by climate change. Within plant communities, soil spatial heterogeneity can potentially buffer the effects of plant freezing stress by increasing the availability of soil microsites that function as microrefugia. Moreover, increased species richness resulting from soil heterogeneity can increase the likelihood of stress‐tolerant species being present in a community. We used a field experiment to examine interactions between soil heterogeneity and increased freezing intensity (achieved via snow removal) on plant abundance and diversity in a grassland. Patches of topsoil were mixed with either sand or woodchips to create heterogeneous and homogeneous treatments, and plant community responses to snow removal were assessed over three growing seasons. Soil heterogeneity interacted significantly with snow removal, but it either buffered or exacerbated the snow removal response depending on the specific substrate (sand vs. woodchips) and plant functional group. In turn, snow removal influenced plant responses to soil heterogeneity; for example, adventive forb cover responded to increased heterogeneity under ambient snow cover, but this effect diminished with snow removal. Our results reveal that soil heterogeneity can play an important role in determining plant responses to changes in soil freezing stress resulting from global climate change. While the deliberate creation of soil microsites in ecological restoration projects as a land management practice could increase the frequency of microrefugia that mitigate plant community responses to increased freezing stress, the design of these microsites must be optimized, given that soil heterogeneity also has the potential to exacerbate freezing stress responses.     

Future ocean climate homogenizes communities across habitats through diversity loss and rise of generalist species

Predictions of the effects of global change on ecological communities are largely based on single habitats. Yet in nature, habitats are interconnected through the exchange of energy and organisms, and the responses of local communities may not extend to emerging community networks (i.e., metacommunities). Using large mesocosms and meiofauna communities as a model system, we investigated the interactive effects of ocean warming and acidification on the structure of marine metacommunities from three shallow‐water habitats: sandy soft‐bottoms, marine vegetation, and rocky reef substrates. Primary producers and detritus—key food sources for meiofauna—increased in biomass under the combined effect of temperature and acidification. The enhanced bottom‐up forcing boosted nematode densities but impoverished the functional and trophic diversity of nematode metacommunities. The combined climate stressors further homogenized meiofauna communities across habitats. Under present‐day conditions metacommunities were structured by habitat type, but under future conditions they showed an unstructured random pattern with fast‐growing generalist species dominating the communities of all habitats. Homogenization was likely driven by local species extinctions, reducing interspecific competition that otherwise could have prevented single species from dominating multiple niches. Our findings reveal that climate change may simplify metacommunity structure and prompt biodiversity loss, which may affect the biological organization and resilience of marine communities.     

Genetic effects of habitat restoration in the Laurentian Great Lakes: an assessment of lake sturgeon origin and genetic diversity

Lake sturgeon (Acipenser fulvescens) have experienced significant habitat loss, resulting in reduced population sizes. Three artificial reefs were built in the Huron‐Erie corridor in the Great Lakes to replace lost spawning habitat. Genetic data were collected to determine the source and numbers of adult lake sturgeon spawning on the reefs and to determine if the founder effect resulted in reduced genetic diversity. DNA was extracted from larval tail clips and 12 microsatellite loci were amplified. Larval genotypes were then compared to 22 previously studied spawning lake sturgeon populations in the Great Lakes to determine the source of the parental population. The effective number of breeders (N_b) was calculated for each reef cohort. The larval genotypes were then compared to the source population to determine if there were any losses in genetic diversity that are indicative of the founder effect. The St. Clair and Detroit River adult populations were found to be the source parental population for the larvae collected on all three artificial reefs. There were large numbers of contributing adults relative to the number of sampled larvae. There was no significant difference between levels of genetic diversity in the source population and larval samples from the artificial reefs; however, there is some evidence for a genetic bottleneck in the reef populations likely due to the founder effect. Habitat restoration in the Huron‐Erie corridor is likely resulting in increased habitat for the large lake sturgeon population in the system and in maintenance of the population's genetic diversity.     

Bird species richness patterns of northern Taiwan: primary productivity, human population density, and habitat heterogeneity

Energy, climate, habitat heterogeneity, and human activity are important correlates of spatial variation in species richness. We examined the correlation between species richness and these variables using the birds that breed in northern Taiwan. We conducted general linear models (GLMs) and spatial correlation models to examine the relationship between bird species richness (BSR) and environmental variables. We found that normalized difference vegetation index (NDVI) was the most important predictor of BSR. We suggest productivity is the primary process of BSR. Additionally, we hypothesized that scale dependency might exist in the relationship between BSR and NDVI in Taiwan. Human population density, the second most important factor, was inversely correlated with BSR. The factor and BSR did not have similar response to NDVI, which contradicted observations in most of the previous studies on human population vs. species richness. We proposed that the human population density had an effect on NDVI, which in turn had an effect on BSR. Moreover, we hypothesized that the contradiction between our study and the previous studies might arise from a higher level of human disturbance in Taiwan than in other areas. The necessity of conserving native species in intensively developed lowlands of Taiwan cannot be overemphasized. Number of land cover type was another significant predictor of BSR. Habitat heterogeneity may have an effect on BSR in Taiwan.     

Mosquito (Diptera: Culicidae) diversity along a rainy season and edge effects in a riparian forest in Southeastern Brazil

Knowledge on the distribution of mosquito communities over time and across human-modified landscapes is important in determining the risk for vector-borne disease. The diversity of mosquitoes along a rainy season and edge effects were evaluated in a riparian forest in the Cerrado biome, Southeastern Brazil. Mosquito communities were sampled with Shannon traps in three distinct habitats (forest interior, forest edge and pasture) throughout an entire rainy season, comprising five sampling months (December 2015 to April 2016). A total of 13 549 mosquitoes belonging to 54 species were sampled. Mosquito species richness and abundance were greater in February, which coincided with the middle of the rainy season and just after the months with greater rainfall. Mosquito species richness did not differ among habitats for any particular month. In February, month when 74% of individuals were recorded, mosquito abundance was lower in the pasture compared with the forest edge and interior, which did not differ statistically from each other. Four of the six most abundant mosquito species (which account for 93.5% of the sampled individuals) had more individuals collected in the forest edge, and 28 species were more abundant at the edge compared with 15 species in the forest interior. Months with high rainfall probably allowed the availability and maintenance of high-water level in breeding sites leading to a further increase in mosquito populations. While the pasture did not seem to have the ideal abiotic conditions and/or resources (e.g. food and breeding sites) for mosquito species, edge effects appear to favour mosquito populations. Therefore, the risk of mosquito-borne diseases is expected to be greater in the middle of the rain season at the riparian forest-pasture edge, when and where a greater number of disease-vectoring species are present.     

Linking small-scale topography with microclimate,plant species diversity and intra-specific trait variation in an alpine landscape

Background: Small-scale topographic complexity is a characteristic feature of alpine landscapes, with important effects on alpine plant distribution.

Aims: We investigated the links between small-scale topographic complexity and resultant microclimatic heterogeneity, vascular-plant species richness and beta diversity, and realised niche width and trait variation of some target species.

Methods: We recorded temperature and soil moisture within 10 sites (40 m × 40 m) of differing topographic complexity in alpine terrain at Finse, Norway (N 60° 36?, E 7° 33?). Plant species occurrence and traits of target species were recorded in 16 sample plots at each site.

Results: Sites differed significantly in microclimatic heterogeneity, and topographically rough sites were always more heterogeneous than flatter ones. Greater species richness and turnover was associated with greater microclimatic heterogeneity, and rough sites contained 15–55% more species than flatter ones. Plant species had on average wider realised niches when growing at rough sites. Individuals of Bistorta vivipara, but not those of Luzula spicata, tended to exhibit greater phenotypic variation at rough sites.

Conclusions: Rough alpine terrains create small-scale variation in microclimate, promoting species richness and beta diversity. In the event of climate change, small-scale microclimatic heterogeneity might allow plant species to escape from regional climate change by short-distance migration to local micro-refugia. This study suggests that the opportunity for such responses would be greater in topographically complex terrains.     

Habitat heterogeneity as a driver of ungulate diversity and distribution patterns: interaction of body mass and digestive strategy

Aim Classic island biogeographical theory predicts that reserves have to be large to conserve high biodiversity. Recent literature, however, suggests that habitat heterogeneity can counterbalance the effect of small reserve size. For savanna ungulates, body mass is said to drive habitat selection and facilitate species coexistence, where large species use a higher proportion of the landscape than smaller species, because a wider food quality tolerance allows them to use a higher diversity of habitat types. In this case, high habitat heterogeneity would facilitate diverse assemblages of different‐sized ungulates. Digestive physiology should further modify this relationship, because non‐ruminants have a wider diet tolerance than ruminants. We tested this hypothesis with an empirical dataset on distribution and habitat preference of different‐sized African grazers. Location Hluhluwe‐iMfolozi Park, Republic of South Africa. Methods We recorded herbivore dung and habitat type on 24 line transects varying between 4 and 11 km with a total length of 190 km to determine habitat selection and landscape distribution of six grazer species, three ruminants and three non‐ruminants. Results Larger ruminant grazers were more evenly distributed than smaller ruminants, had a more diverse use of habitats and used more low quality habitat. In contrast, non‐ruminant grazers were more evenly distributed than similar‐sized ruminants and body mass did not clearly influence diversity of habitat use and use of low quality habitat. Main conclusions We confirm that body mass influences diversity of habitat use of large herbivores but digestive strategy potentially modifies this relationship. Hence, habitat heterogeneity might facilitate herbivore diversity in savanna ecosystems and high heterogeneity might counterbalance the effects of fragmentation and declining reserve size. Concluding, processes that homogenize the landscape, such as fire (mis)management and artificial waterholes, might be as threatening to biodiversity as landscape fragmentation, especially for smaller ruminant herbivores.     

Whales in warming water: Assessing breeding habitat diversity and adaptability in Oceania's changing climate

In the context of a changing climate, understanding the environmental drivers of marine megafauna distribution is important for conservation success. The extent of humpback whale breeding habitats and the impact of temperature variation on their availability are both unknown. We used 19 years of dedicated survey data from seven countries and territories of Oceania (1,376 survey days), to investigate humpback whale breeding habitat diversity and adaptability to climate change. At a fine scale (1 km resolution), seabed topography was identified as an important influence on humpback whale distribution. The shallowest waters close to shore or in lagoons were favored, although humpback whales also showed flexible habitat use patterns with respect to shallow offshore features such as seamounts. At a coarse scale (1° resolution), humpback whale breeding habitats in Oceania spanned a thermal range of 22.3–27.8°C in August, with interannual variation up to 2.0°C. Within this range, both fine and coarse scale analyses of humpback whale distribution suggested local responses to temperature. Notably, the most detailed dataset was available from New Caledonia (774 survey days, 1996–2017), where encounter rates showed a negative relationship to sea surface temperature, but were not related to the El Niño Southern Oscillation or the Antarctic Oscillation from previous summer, a proxy for feeding conditions that may impact breeding patterns. Many breeding sites that are currently occupied are predicted to become unsuitably warm for this species (>28°C) by the end of the 21st century. Based on modeled ecological relationships, there are suitable habitats for relocation in archipelagos and seamounts of southern Oceania. Although distribution shifts might be restrained by philopatry, the apparent plasticity of humpback whale habitat use patterns and the extent of suitable habitats support an adaptive capacity to ocean warming in Oceania breeding grounds.