Floodplain biodiversity: why are there so many species?

Spring surveys of 112 temporary floodplain waters on River Murray tributaries demonstrated a heterogeneous habitat series, with ca. 500 species of microfauna encountered. Rotifers comprised the most diverse group (>250 taxa), however mean diversity was low (10.93 ± 7.5), in part reflecting predation by copepods and macroinvertebrates. Notably, only 10 rotifer species could be considered widespread in the study area. Ephemeral pool microfaunal communities were distinct from those of adjacent permanent billabongs; their community variability is seen as a function of, or response to, habitat heterogeneity. The significance of high species diversity in ephemeral waters is considered in the context of age of the Murray-Darling Basin, which has persisted in its present location since the breakup of Gondwana, >65 MY BP.

Surface water in arid regions is essential to many organisms including large mammals of conservation concern. For many regions little is known about the extent, ecology and hydrology of ephemeral waters, because they are challenging to map given their ephemeral nature and small sizes. Our goal was to advance surface water knowledge by mapping and monitoring ephemeral water from the wet to dry seasons across the Kavango–Zambezi Transfrontier Conservation Area of southern Africa (300 000 km2). We mapped individual waterholes for six time points each year from mid-2017 to mid-2020, and described their presence, extent, duration, variability, and recurrence. We further analyzed a wide range of physical and landscape aspects of waterhole locations, including soils, geology, and topography, to climate and soil moisture. We identified 2.1 million previously unmapped ephemeral waterholes (85%–89% accuracy) that seasonally extend across 23.5% of the study area. We confirmed a distinct ‘blue wave’ with ephemeral water across the region peaking at the end of the rainy season. We observed a wide range of waterhole types and sizes, with large variances in seasonal and interannual hydrology. We found that ephemeral surface water was associated with loam soils in the study area. From the wettest time period to the driest, there was a ∼44 000 km2 (62%) decrease in ephemeral water extent across the region—these dramatic seasonal fluctuations have implications for wildlife movement. A warmer and drier climate, expected human population growth, and associated agricultural expansion and development may threaten these sensitive and highly variable water resources and the wildlife that depend on them.

(introduction to Special Issue: The roles of habitat heterogeneity in generating and maintaining biodiversity on continental margins A Contribution to the Census of Marine Life)

In many savannah regions of Africa, pronounced seasonal variability in rainfall results in wildlife being restricted to floodplains and other habitats adjacent to permanent surface water in the dry season. During the wet season, rainfall fills small-scale, ephemeral water sources that allow wildlife to exploit forage and other resources far from permanent surface water. These water sources remain difficult to quantify, however, due to their small and ephemeral nature, and as a result are rarely included in quantitative studies of wildlife distribution, abundance, and movement. Our goal was to map ephemeral water in Bwabwata National Park in Namibia using two different approaches and to relate measures of ephemeral water to the abundance, distribution, and movement of two large wildlife species. We used high-resolution Google Earth and Esri World imagery to visually identify waterholes. Additionally, we used Sentinel-2 satellite imagery to map ephemeral water across the study area using the Normalized Difference Water Index. With these mapped waterhole layers and data from GPS-collared individuals of African elephant (Loxodonta africana) and African buffalo (Syncerus caffer), we evaluated the importance of ephemeral water in conditioning abundance and movement of these two species. The two approaches to mapping ephemeral water resulted in the visual identification of nearly 10,000 waterholes, and a predicted ephemeral water layer of ~76% accuracy. The inclusion of ephemeral water into models of abundance and movement resulted in improved goodness of fit relative to those without water, and water impacts on abundance and movement were among the strongest of all variables considered. The potential importance of ephemeral water in conditioning the movements and distributions of large herbivores in African savannahs has been difficult to quantify relative to vegetation drivers. Our results suggest research into ephemeral water impacts deserves more attention.

Both habitat heterogeneity and disturbance can profoundly influence ecological systems at many levels of biological and ecological organization. However, the joint influences of heterogeneity and disturbance on temporal variability in communities have received little attention despite the intense homogenizing influence of human activity. I performed a field manipulation of substrate heterogeneity in a small New England stream, and measured changes in benthic macroinvertebrate communities for 100 days—a period that included both a severe drought and a flood. Generally, community variability decreased with increasing substrate heterogeneity. However, within sampling intervals, this relationship tended to fluctuate through time, apparently tracking changes in hydrology. At the beginning of the experiment, community temporal variability clearly decreased along a gradient of increasing substrate heterogeneity—a result consistent with an observational study performed the previous year. During the subsequent weeks, droughts and flooding created exceptionally high variability in both hydrology and benthic macroinvertebrate community structure resulting in the disappearance of this relationship. However, during the last weeks of the experiment when hydrologic conditions were relatively more stable, the negatively sloped relationship between community temporal variability and habitat heterogeneity reemerged and mimicked relationships observed both early in the experiment and in the previous year’s study. High habitat heterogeneity may promote temporal stability through several mechanisms including stabilization of resources and increased refugia from minor disturbances or predation. However, the results of this experiment suggest that severe disturbance events can create large-scale environmental variability that effectively swamps the influence of habitat heterogeneity, illustrating that a thorough understanding of community temporal variability in natural systems will necessarily consider sources of environmental variability at multiple spatial and temporal scales.

Restoration has the potential to increase habitat heterogeneity through the creation of unique habitat patches that, in turn, increase regional species richness or gamma diversity. While biological diversity and habitat heterogeneity are important factors to consider under a shifting climate, restoration actions and outcomes rarely examine these components. In this study, we examined the effects of riparian beaver dam analog (BDA) restoration on aquatic invertebrate diversity and habitat heterogeneity. Although the effects of BDAs on hydrology, geomorphology, and salmonid habitat have been explored, we are unaware of any studies assessing their effects on aquatic invertebrate diversity and the food web that supports them. We sampled aquatic invertebrates, basal carbon resources, dissolved nutrients, turbidity, and water temperature in pre‐ and post‐BDA pond, side channel, and mainstem habitat over a three‐year period. The BDAs functioned similarly to natural beaver dams and created slow‐water environments that accumulated fine particulate organic material and increased pelagic phytoplankton production. Nonmetric multidimensional scaling, permutation multivariate analysis of variance, and Mantel's tests demonstrated that these changes led to the formation of a unique invertebrate community populated by lentic macroinvertebrates and zooplankton, which increased beta‐diversity and gamma diversity. Further, BDAs in our study maintained high densities of invertebrates and buffered water temperatures in comparison to adjacent lotic habitats. These results support our hypothesis that BDAs can enhance invertebrate beta and gamma diversity through the creation and colonization of unique pond habitat and improve habitat and resource heterogeneity for native fishes under variable climate conditions.

The relationship between mammal community structure and vertical variation in habitat physiognomy (complexity) and horizontal variation in habitat form (heterogeneity) was examined on five study areas in the llanos of Venezuela. Data on the small mammal (<1 kg) of the study sites were obtained through a mark—recapture trapping program of >38 000 trap nights from 1976—1978. Data on the distribution of large, nonvolant mammals were obtained during 24 mo of field observation. Measures of habitat complexity and habitat heterogeneity were derived using principal components analysis. There was little association between habitat structure and the richness, diversity, abundance, and biomass of small mammals. Abiotic factors, such as the degree of wet—season flooding, probably play an important role in patterns of small mammal distribution and abundance. The total number of mammal species was positively correlated with habitat complexity but not correlated with habitat heterogeneity. Increasing species richness across the complexity gradient was probably accommodated by increasing potential food resources. New species were added to complex communities primarily through guild expansion rather than guild addition.

Environmental and biotic habitat attributes affect rocky intertidal community variability in glacially influenced estuaries

Diverse microbial communities thrive on and in deep-sea hydrothermal vent mineral deposits. However, our understanding of the inter-field variability in these communities is poor, as limited sampling and sequencing efforts have hampered most previous studies. To explore the inter-field variability in these communities, we used barcoded pyrosequencing of the variable region 4 (V4) of the 16S rRNA gene to characterize the archaeal and bacterial communities of over 30 hydrothermal deposit samples from six vent fields located along the Eastern Lau Spreading Center. Overall, the bacterial and archaeal communities of the Eastern Lau Spreading Center are similar to other active vent deposits, with a high diversity of Epsilonproteobacteria and thermophilic Archaea. However, the archaeal and bacterial communities from the southernmost vent field, Mariner, were significantly different from the other vent fields. At Mariner, the epsilonproteobacterial genus Nautilia and the archaeal family Thermococcaceae were prevalent in most samples, while Lebetimonas and Thermofilaceae were more abundant at the other vent fields. These differences appear to be influenced in part by the unique geochemistry of the Mariner fluids resulting from active degassing of a subsurface magma chamber. These results show that microbial communities associated with hydrothermal vent deposits in back-arc basins are taxonomically similar to those from mid-ocean ridge systems, but differences in geologic processes between vent fields in a back-arc basin can influence microbial community structure.

QuestionsTo what extent is species richness in semi‐natural grasslands related to local environmental factors and (present/past) surrounding landscape structure? Do responses of species richness depend on degree of habitat specialization (specialists vs generalists) and/or scale of the study?LocationÖland, Sweden.MethodsRichness of herbaceous vascular plants (subdivided into richness of grassland specialists and generalists) was recorded within 50 × 50 cm plots and 0.1–4.8 ha grassland polygons. Generalized linear models and hierarchical partitioning were used to identify local factors (habitat area and heterogeneity, grazing intensity, habitat continuity) and landscape factors (proportion of surrounding grassland in 2004, 1938 and 1800, and landscape diversity in 2004) associated with the richness estimates.ResultsAt the polygon scale, both specialist and generalist richness was positively associated with local habitat area and heterogeneity and, independently of area and heterogeneity, with grazing intensity, habitat continuity and amount of surrounding grassland in 1800. At the plot scale, specialist species richness was positively associated with habitat heterogeneity, amount of surrounding grassland in 2004 and landscape diversity. Plot‐scale generalist richness was negatively associated with surrounding grassland in 1938 and positively associated with local grazing intensity.ConclusionsBecause both habitat specialization and study scale influence conclusions about relationships between species richness and local and landscape factors, the study highlights the need to consider species diversity at multiple spatial scales when making decisions about grassland management. Large‐scale (polygon) species richness is influenced by immigration processes, with both specialists and generalists accumulating in old grasslands over centuries of grazing management. Habitat heterogeneity increased specialist species richness at both scales, suggesting that management policies should favour maintenance of a heterogeneous mosaic of open areas, trees and shrubs in temperate grazed grasslands. Although grassland specialists are sensitive to grassland isolation, in extensively managed landscapes with high landscape diversity input of grassland species from the landscape matrix may buffer negative effects of habitat fragmentation on grassland communities.

Research Article| December 01, 2011 MINERALOGICAL, GEOCHEMICAL AND STRUCTURAL CHARACTERISTICS OF QUARTZ-ARENITES OF THE WITPOORT FORMATION (CAPE SUPERGROUP) NEAR KIRKWOOD, EASTERN CAPE, SOUTH AFRICA W.C. OLIVIER; W.C. OLIVIER Department of Geosciences, P O Box 77000, Nelson Mandela Metropolitan University, Port Elizabeth, 6031, South Africa, e-mail: wcolie4@gmail.com Search for other works by this author on: GSW Google Scholar P.W.K. BOOTH; P.W.K. BOOTH Department of Geosciences, PO Box 77000, Nelson Mandela Metropolitan University, Port Elizabeth, 6031 South Africa, e-mail: Peter.Booth@nmmu.ac.za (corresponding author) Search for other works by this author on: GSW Google Scholar C.R. ANDERSON C.R. ANDERSON Department of Geosciences, PO Box 77000, Nelson Mandela Metropolitan University, Port Elizabeth, 6031 South Africa, e-mail: Callum.Anderson@nmmu.ac.za Search for other works by this author on: GSW Google Scholar Author and Article Information W.C. OLIVIER Department of Geosciences, P O Box 77000, Nelson Mandela Metropolitan University, Port Elizabeth, 6031, South Africa, e-mail: wcolie4@gmail.com P.W.K. BOOTH Department of Geosciences, PO Box 77000, Nelson Mandela Metropolitan University, Port Elizabeth, 6031 South Africa, e-mail: Peter.Booth@nmmu.ac.za (corresponding author) C.R. ANDERSON Department of Geosciences, PO Box 77000, Nelson Mandela Metropolitan University, Port Elizabeth, 6031 South Africa, e-mail: Callum.Anderson@nmmu.ac.za Publisher: Geological Society of South Africa First Online: 09 Mar 2017 Online ISSN: 1996-8590 Print ISSN: 1012-0750 © 2011 Geological Society of South Africa South African Journal of Geology (2011) 114 (3-4): 249–264. https://doi.org/10.2113/gssajg.114.3-4.249 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation W.C. OLIVIER, P.W.K. BOOTH, C.R. ANDERSON; MINERALOGICAL, GEOCHEMICAL AND STRUCTURAL CHARACTERISTICS OF QUARTZ-ARENITES OF THE WITPOORT FORMATION (CAPE SUPERGROUP) NEAR KIRKWOOD, EASTERN CAPE, SOUTH AFRICA. South African Journal of Geology 2011;; 114 (3-4): 249–264. doi: https://doi.org/10.2113/gssajg.114.3-4.249 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract A study of Late Palaeozoic Witteberg Group rocks (Cape Supergroup) near Kirkwood, Eastern Cape was carried out to determine the viability of extracting silica for solar cell production. Mineralogical, geochemical and structural analyses of selected outcrops of quartz-arenites showed that source rocks in the study area do not possess the appropriate chemical attributes to warrant extraction of silica. Despite this finding the study presents valuable information on strata composition and structural data which are compared and interpreted with known regional structural patterns of the Cape Fold Belt in the Eastern Cape.Samples from the Witpoort Formation were analyzed using petrographic light microscopy, scanning electron microscopy and X-ray fluorescent spectroscopy. Analyses indicate that samples are composed almost entirely of quartz, with accessory biotite, muscovite, sericite, baryte, apatite, rutile and monazite. Haematite occurs most frequently along fractures, and is more prevalent in the Rooirand Member than the Perdepoort Member, giving the former a reddish brown colour on outcrop. The presence of chemical impurities is thought to be partly controlled by the original depositional environment, namely, near-shore and beach environments.Strata in the study area display a range of fold styles, mostly showing northward vergence. Low angle thrust faults dip south and some thrusts dip north. In general, the orientation of fore-thrusts and folds in the study area indicate a northward-directed compression event during the Late Palaeozoic. This pattern conforms to the structural development in other parts of the Cape Fold Belt in the Eastern Cape. South-dipping normal faults and strike-slip faults post-date thrust faulting, and formed during the breakup of Gondwana, during the Mesozoic, transecting all other structures in the study area. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Environmental heterogeneity has a consistent, positive effect on species diversity globally, principally due to increased niche space in heterogeneous environments. In flammable ecosystems, fire‐mediated heterogeneity (pyrodiversity) is expected to increase species diversity, and the application of diverse fire regimes is a common management goal. We used landscape‐scale sampling units and linear mixed models to determine the response of ground‐dwelling mammal alpha, beta, and gamma diversity to spatial habitat heterogeneity (functional heterogeneity) and three indirect measures of spatial heterogeneity, two pyrodiversity indices based on fire history maps, and another based on mapped vegetation types. In addition, we tested the consistency of species diversity responses across a productivity gradient and examined the extent to which prescribed fire influenced habitat heterogeneity. Beta diversity responded positively to habitat heterogeneity across the productivity gradient, but more strongly at high compared with low productivity. In contrast, alpha and gamma diversity responded positively to productivity, while a weak negative effect of habitat heterogeneity on alpha diversity was also evident. At the scale of our investigation, the productivity gradient across the study area was the most influential driver of species diversity. Spatial heterogeneity within 100‐ha landscapes increased community differentiation among sites (beta diversity), had a weak negative effect on alpha diversity, but had no influence on landscape‐scale species richness (gamma diversity). The occurrence of recent fire had a strong, positive effect on habitat heterogeneity, while the diversity of vegetation types and postfire age classes had a smaller positive influence. Our findings show that prescribed fire can be used to increase landscape‐scale structural heterogeneity, but this will not always result in additional species. Finally, we suggest that using a functional representation of spatial heterogeneity (e.g., the spatial arrangement of habitat structure) as a predictor of species diversity is likely to reveal responses that may otherwise be overlooked. Modern remote‐sensing technologies will aid the development of habitat‐based heterogeneity metrics across large spatial extents.

Studying the response of assemblages either tonatural or human induced environmental gradients is challenging due to spatial and temporal heterogeneity in river systems. This study identified the relationship between environmental variables, as well as sampling date, and Ephemeroptera (E), Plecoptera (P), Trichoptera (T) assemblages in a karst river system. Each assemblage component (E, P, T, EP, ET, PT, and EPT) is analyzed separately. Ten direct influential variables (water depth, water temperature, current velocity, dissolved oxygen concentration, oxygen saturation, pH, nitrate concentration, total solids, and total suspended solids) and sampling date were considered in order to identify environmental gradients after removal of the effect of stream size and habitat heterogeneity; both parameters were used as covariables. Thus, the observed effects of selected 10 variables were those that were not explained also by Strahler stream order and habitat heterogeneity. Examination of the EPT assemblage characteristics using the non-parametric Kruskal–Wallis test showed significant spatial variations in richness/diversity metrics (number of EPT taxa, Shannon–Wiener diversity) but not in functional metrics (Gatherers/Collectors, Grazers, and Scrapers). The temporal variation in all metrics was substantial. Assemblage variances (R 2 ) and adjustedassemblagevariances (R 2 adj )of>35% and>20%,respectively, were obtained. Main environmental gradients representing hydrogeology and eutrophication as well as hydraulic and oxygen gradient for EPT assemblages were recognized. It appears that eutrophication is the key ecological factor for most assemblage components in a Dinaric karst river system, although Plecoptera assemblages were best explained by temperature regime and oxygen conditions. This studysuggeststhatavariationinthediversity betweenE,P,andTtaxainfluences anassemblage– environment relationship. Environmental variables that were best predictors for assemblages with more than one insect group were associated with assemblages with high diversity. This study provides methods and approaches to recognize the main factors determining biotic assemblages’ structures in Dinaric karst river systems and thus provides a basis to develop appropriate biodiversity conservation policies.

Questions: How long may it take for desert perennial vegetation to recover from prolonged human disturbance and how do different plant community variables (i.e. diversity, density and cover) change during the recovery process?Location: Sonoran Desert, Arizona, USA.Methods: Since protection from grazing from 1907 onwards, plant diversity, density and cover of perennial species were monitored intermittently on ten 10 m × 10 m permanent plots on Tumamoc Hill, Tucson, Arizona, USA.Results: The study shows an exceptionally slow recovery of perennial vegetation from prolonged heavy grazing and other human impacts. Since protection, overall species richness and habitat heterogeneity at the study site continued to increase until the 1960s when diversity, density and cover had been stabilized. During the same period, overall plant density and cover also increased. Species turnover increased gradually with time but no significant relation between any of the three community variables and precipitation or Palmer Drought Severity Index (PDSI) was detected.Conclusions: It took more than 50 yr for the perennial vegetation to recover from prolonged human disturbance. The increases in plant species richness, density, and cover of the perennial vegetation were mostly due to the increase of herbaceous species, especially palatable species. The lack of a clear relationship between environment (e.g. precipitation) and community variables suggests that site history and plant life history must be taken into account in examining the nature of vegetation recovery processes after disturbance.

Aquatic macrophytes serve as shelter and a direct source of food for invertebrates, in addition to indirectly providing items such as algae, detritus, and microorganisms. Thus, aquatic macrophytes act as habitat structuring elements, requiring a distinction between habitat complexity (physical formations such as fractal dimensions, density and biomass) and habitat heterogeneity (diversity of these structures). Here we explore the effects of habitat complexity and habitat heterogeneity on the invertebrate community. We collected macrophytes and invertebrates from 28 sampling sites along a 13.7‐km stretch of the Baía River in Brazil, and examined specific groups (insects, microcrustaceans, and other invertebrates). Environmental variables in the sites were also measured. We aimed to explore the effects of habitat complexity (measured by macrophyte biomass) and habitat heterogeneity (evaluated through macrophyte functional diversity) on the richness and abundance of invertebrates. We found that overall invertebrate richness was positively influenced solely by habitat heterogeneity. For invertebrate abundance, intermediate habitat complexity had more invertebrates, while habitat heterogeneity had a positive impact. Environmental variables influenced only the abundance. For specific groups, insect richness was positively influenced by habitat heterogeneity, while insect abundance decreased with high complexity and increased with high heterogeneity. Microcrustacean abundance was positively influenced by habitat complexity. Richness and abundance of other invertebrates was positively influenced by habitat heterogeneity. Invertebrates prefer macrophyte stands with intermediate complexity and high heterogeneity. Abundance is linked to structural complexity and heterogeneity, while species richness is more strongly associated with heterogeneity. Furthermore, the impact of these factors varies among invertebrate groups. These findings emphasise the importance of integrating a broad range of metrics, such as macrophyte biomass and functional diversity, to gain a thorough understanding of invertebrate community dynamics in future studies. Additionally, our study demonstrates that preserving macrophyte stands with high heterogeneity significantly enhances the diversity of associated invertebrate species.