Contrasting responses of Odonata diversity to the rainy season in lentic and lotic habitats in Colombia

Floods and droughts are 2 of the most influential factors affecting the structure and function of benthic macroinverte-brate assemblages in stream ecosystems. Even if these natural disturbances occur at the same magnitude at multiple research sites, the responses may differ according to stream type. In our study, we examined the various responses of functional feeding guilds (FFGs), related to the feeding methods and food types of macroinvertebrates, and habit trait guilds (HTGs), related to the mobility of macroinvertebrates and location of food obtained, to floods and droughts in different stream types (perennial, intermittent, or ephemeral). The stream types were categorised according to the stream flow conditions, flow permanence, and stream connectivity. Perennial streams were those maintaining continuous lotic habitats; intermittent streams were lotic habitats during periods of heavy rain but either connected or isolated pools during dry periods; and ephemeral streams existed only during the rainy season. Among the substrates, cobbles and boulders were highly dominant during heavy rain, especially in the first periods of heavy rain, whereas silt and sand were more often present in high proportions at intermittent stream sites. Across all stream types, highly intense and heavy rain led to a decrease in species richness and abundance, with changes in the composition of both FFGs and HTGs. Organisms characterised as scrapers and/or clingers (e.g., Ecdyonurus dracon, E. levis, and Simuliidae sp.), were highly resistant to high discharge compared to other FFGs or HTGs and were dominant during floods. In dry periods, the composition and richness of FFGs and HTGs were more affected at intermittent streams than at perennial streams. Long-lasting dry periods consistently reduced lotic habitat abundance and diversity and increased the amount of lentic habitats as well as zones with sedimentation, especially at intermittent stream sites, resulting in a decrease in collector-filterer organisms and an increase in burrowers (e.g., Ephemera strigata). Despite seasonal predictability, however, floods of relatively lower magnitude and intensity provided opportunities for some species, especially clingers (e.g., Epeorus pellucidus) and swimmers (e.g., Baetis fuscatus), to be introduced and/or become established in new habitats downstream in the ephemeral streams. Our research indicated that spatial (i.e., stream type) and temporal (i.e., floods and drying events) heterogeneities are the defining factors that influence functional diversity in benthic macroinvertebrate communities.

Lentic and lotic habitats support distinct aquatic communities, yet how environmental gradients and anthropogenic pressure differentially shape diversity patterns across these habitat types remains poorly understood. Here, we examined Odonata alpha and beta diversity across lentic and lotic habitats in northeastern Algeria to assess habitat‐specific responses to environmental and anthropogenic drivers. We sampled adult Odonata and measured local environmental variables at 35 sites, complemented by climatic and anthropogenic data from global datasets. Alpha diversity was quantified using coverage‐based Hill numbers, beta diversity was partitioned into turnover and nestedness components and environmental drivers were assessed using constrained ordination and generalised linear mixed models. We recorded 40 species, with significantly higher asymptotic richness and Simpson diversity in lotic than lentic habitats. Human Footprint Index (HFI) exhibited habitat‐dependent effects on species richness (HFI × habitat: β = −0.352, 95% CI: −0.673 to −0.030), with lotic habitats showing negative responses to anthropogenic pressure while lentic habitats exhibited a positive association. Community composition differed significantly between habitat types and was primarily structured by altitude. Beta diversity was dominated by turnover rather than nestedness, with significantly higher total dissimilarity in lentic habitats. Our findings suggest that conservation strategies for Mediterranean Odonata diversity require a landscape approach that protects both habitat types while recognising their differential sensitivity to human impacts.

Lentic and lotic habitats, combined with varying altitudes, may have differential effects on communities of the Order Odonata. We sampled adult odonates at 94 waterbodies of the Orinoquía region of eastern Colombia. Our hypothesis was that species composition and richness, as well as abundance, would be affected by both altitude and habitat. Overall, 70 of the 100 species recorded in the study were sampled in both lotic and lentic environments, with 16 species (5 in the Suborder Zygoptera and 11 in the Suborder Anisoptera) occurring only in lentic habitats and 14 occurring exclusively in lotic habitats (13 Zygoptera, 1 Anisoptera). The results of the analysis indicated that the species richness and abundance of anisopterans were affected by altitude, whereas the diversity of zygopterans was not affected in any way. Despite these mixed findings, the results for anisopterans were consistent with the results of previous studies, which have indicated altitude as a primary determinant of the Odonata diversity through its effect on the dynamics of water flow and the shift from lentic to more lotic environments. Further studies over a more ample altitudinal gradient should provide more conclusive evidence, particularly regarding the role played by both altitude and habitat on the local diversity of odonates.

River damming alters the physical–chemical variables of water and often causes compartmentalisation of aquatic habitats. Seasonality can add complexity to the longitudinal compartmentalisation. The spatial and temporal effects of these two phenomena on the structure of ichthyofauna from a tributary under the influence of damming were evaluated, based on the following hypotheses: (1) transition habitats have the greatest species richness; (2) community similarity decreases with increasing distance between sites; (3) conservation of free‐flowing areas upstream reservoir contributes to the maintenance of migratory species. To evaluate the effects of these two phenomena, twelve monthly fish samples (September/12 to August/13) were performed with gillnets in three sample areas distributed longitudinally in the tributary. Limnological variables were measured in the same sample areas to confirm compartmentalisation. We observed three distinct limnological compartments (lotic, transition and lentic), with increase differentiation during the rainy season. This compartmentalisation influenced fish fauna where localised communities exhibited different compositions among the three sampled habitats. During the rainy season, these differences become pronounced, with transition habitat showing greater species richness than the others. More pronounced differences in species composition and structure in extremes sampling sites were also observed. Migratory fish presented higher proportion of fish composition in lotic habitat. In conclusion, damming and seasonality acted concomitantly as modulators of fish fauna in a tributary influenced by damming. However, compartmentalisation of habitats was the primary driver of ichthyofauna community structure with the rainy season increasing differences in community composition.

SUMMARYThe morphology and phenology of a monoecious population ofSirodotia suecicaKylin was evaluated seasonally in a central Mexican fifth‐order high‐altitude stream. Abundance of gametophytes is positively correlated with concentrations of total dissolved solids, specific conductivity and total ionic concentration; being present the whole dry season and disappearing in the rainy season. The gametophytes grew in eutrophic circumstances and particular microhabitat conditions: high current velocity (66–122 cm s−1), low irradiance (75–263 µmol photons m−2 s−1) and shallow depth (7–26 cm). Percent cover of gametophytes ranged from 5–90% and significant differences in abundance were not observed when alga was present. Some morphological and reproductive characteristics seem to be adaptations to high current velocity: abundant secondary branches, spermatangia and carpogonia. ‘Chantransia’ stage, microscopic creeping filaments associated with the base of the gametophyte, were not observed in natural conditions. In terms of reproductive success, the population studied can be regarded as highly efficient, considering the high fertilized carpogonia rate, similar to monoecious populations in lotic habitats. HoweverS. suecicawas not common in the study region because it was restricted to particular microhabitat conditions.

Simple SummaryIntermittent rivers and are an important source of water in arid regions such as the Mediterranean. Water resources and riparian habitats in the Mediterranean regions are under diverse anthropogenic pressures, including the land-use change. We studied Odonata adults at four intermittent Mediterranean rivers in the Dinaric Western Balkans ecoregion, with the aim of inspecting the conservation value of these habitats based on Odonata assemblages and in the context of the surrounding land-cover heterogeneity. We analyzed several diversity and conservation indices and recorded significant differences in Odonata species richness and Croatian Conservation Odonatological index among the studied rivers. Our findings showed that land use, as a long-term moderate anthropogenic impact, can enhance land-cover heterogeneity and in some cases even lead to increased Odonata diversity in the intermittent rivers in the Mediterranean.Intermittent rivers, lotic habitats that cease to flow during the dry periods of the year, make up a large proportion of the world’s inland waters and are an important source of water in arid regions such as the Mediterranean. Yet, water resources and riparian habitats in the Mediterranean regions are under diverse anthropogenic pressures, including land-use change. Odonata are widely used as a valuable tool for assessing freshwater ecosystems. Hence, with the aim of inspecting the conservation value of intermittent rivers in the Mediterranean based on the assemblages they support, we studied Odonata adults at four intermittent Mediterranean rivers in the Dinaric Western Balkans ecoregion with respect to the surrounding land-cover heterogeneity. We analyzed several diversity and conservation indices and recorded significant differences in Odonata species richness and Croatian Conservation Odonatological index among the studied rivers. Our findings showed that land use, as a long-term moderate anthropogenic impact, can enhance land-cover heterogeneity and in some cases even lead to increased Odonata diversity in intermittent rivers in the Mediterranean. Intermittent rivers provide habitat for several threatened Odonata species, suggesting the importance of Odonata in planning the conservation activities in these vulnerable ecosystems.

Summary Understanding multiple ecological determinants of plant diversity and composition underpins good vegetation management. In mesic ecosystems, ecological theory and empirical data predict that moderate to high disturbance promotes native plant diversity, but relationships between disturbance and other drivers of diversity are poorly understood. We examined local determinants of native plant diversity and composition through 12‐year fire, mowing and grazing experiments in two mesic grassy woodland remnants in fragmented agricultural landscapes of south‐eastern Australia. Remnants were representative of diverse woodlands, but had contrasting management histories. We hypothesized that (1) disturbance is a dominant driver of plant diversity and composition and (2) moderate to high disturbance promotes diversity independent of other drivers or disturbance agent. Contrary to our first hypothesis, rainfall explained an overwhelming 31–60% of variation in native plant richness and native forb cover (hereafter diversity), while aspects of disturbance regime accounted for a significant but moderate 3–8%. The magnitude of disturbance effects was often rainfall dependent, and similar to that of other local determinants such as spatial heterogeneity. Disturbance also influenced native forb composition at one site. The direction of disturbance effects on diversity did not depend on disturbance agent, but differed markedly between sites in accordance with their management history. At the cleared site with a history of frequent burning, diversity declined significantly with time since burning or mowing. By contrast, at the long‐unburnt, wooded site, diversity declined with frequent fire and with lagomorph and macropod grazing. These contrasting responses indicate that moderate to high disturbance is not consistently beneficial for diversity in mesic grassy ecosystems, contradicting our second hypothesis. Instead, disturbance responses are dependent on interactions with other drivers, potentially including assemblage filtering associated with historical fire regime and increased understorey productivity associated with tree clearing. Synthesis and applications: The magnitude and direction of disturbance effects on diversity depend on interactions with other drivers, hence a single prescription for disturbance regime across different remnants of fragmented grassy ecosystems is not appropriate. Decadal‐scale responses of diversity to disturbance may be shaped by historical disturbances, suggesting instead that management be guided by historical regime.

Arthropod diversity and assemblage structure response to deforestation and desertification in the Sahel of western Senegal

Biodiversity underpins critical ecological processes, yet its relationship with phosphorus (P) remains poorly understood. Understanding the distinct responses of plant and soil microbial diversity to P availability changes is particularly crucial on a global scale. Integrating meta-analysis and natural gradient approaches, this study evaluates these responses globally. Specifically, we conducted a meta-analysis using 393 observations from 128 field P addition experiments and supplemented this with a natural gradient analysis of forest tree diversity and vascular plant diversity. Our meta-analysis results showed that P additions reduced plant species richness by 8.5% and Shannon index by 1.3% in global grasslands, while exerting minimal effects on soil bacterial and fungal diversity across major terrestrial ecosystems. Natural gradient analysis further demonstrated significant correlations between both forest tree richness and vascular plant richness with soil total P concentrations. Notably, partial correlation analyses showed negative correlations when controlling for gross primary productivity and edaphic variables, but positive correlations when controlling for climatic variables. These complementary approaches collectively suggest that plant diversity exhibits greater sensitivity to altered soil P availability than soil microbial diversity. Consequently, elucidating the differential responses of above- and below-ground biodiversity to nutrient supply changes provides a scientific foundation for sound management of terrestrial ecosystem functions and processes.

Odonate nymphs are important predators of the immature aquatic stages of mosquitoes. Populations of the malaria vector Anopheles pseudopunctipennis Theobald (Diptera: Culicidae) can be efficiently reduced by extraction of filamentous algae from river pools in southern Mexico. Here, we examined the influence of this intervention on the diversity of odonates associated with mosquito breeding pools after annual extractions of algae from river pools in a 3-km section of the Coatan River, over a period of 2 yr. Odonate sampling was performed at monthly intervals in control and treated sections of the river for 4–5 mo after extraction in both years and before extraction in 1 yr. In total, 16 species, 10 genera, and 6 families of odonates were collected. Shannon diversity index values declined significantly during a period of 1 mo in 2001 and >5 mo in 2002. However, the abundance of odonates captured was not affected by algal extraction. In contrast, year-to-year variation in the diversity and abundance of the odonate community was strongly influenced by precipitation and river volume. Despite the importance of algae in river ecology, we conclude that the mosquito control intervention resulted in minimal impact on the odonate community in southern Mexico.

Odonate nymphs are important predators of the immature aquatic stages of mosquitoes. Populations of the malaria vector Anopheles pseudopunctipennis Theobald (Diptera: Culicidae) can be efficiently reduced by extraction of filamentous algae from river pools in southern Mexico. Here, we examined the influence of this intervention on the diversity of odonates associated with mosquito breeding pools after annual extractions of algae from river pools in a 3-km section of the Coatán River, over a period of 2 yr. Odonate sampling was performed at monthly intervals in control and treated sections of the river for 4–5 mo after extraction in both years and before extraction in 1 yr. In total, 16 species, 10 genera, and 6 families of odonates were collected. Shannon diversity index values declined significantly during a period of 1 mo in 2001 and >5 mo in 2002. However, the abundance of odonates captured was not affected by algal extraction. In contrast, year-to-year variation in the diversity and abundance of the odonate community was strongly influenced by precipitation and river volume. Despite the importance of algae in river ecology, we conclude that the mosquito control intervention resulted in minimal impact on the odonate community in southern Mexico.

With agricultural demands increasing globally, determining the nature of impacts of different forms of agriculture on biodiversity, especially for threatened vertebrates and habitats, is critical to inform land management. This is especially true for open ecosystems such as the natural rock outcrops and amphibians, both of which are threatened by land-use change. Lateritic plateaus of the northern Western Ghats are rock outcrop ecosystems harboring endemic biodiversity. Since most of these plateaus are located outside protected areas and officially classified as wastelands, they are rapidly lost due to multiple human pressures, including agriculture. We compared amphibian composition, diversity, and species responses across these rocky plateaus (hereafter plateaus), orchards, and rice paddy in the Western Ghats-Sri Lanka biodiversity Hotspot, India. We sampled 50 belt transects across four geographically separated plateaus, covering three land-use classes in three of the plateaus, and recorded information on amphibians and their microhabitats. Each transect was sampled four times across the rainy season. We compared responses of amphibians across three land-use categories at the community level using Hill numbers, beta-diversity measures, and nonmetric multidimensional scaling, and at the species level using joint species distribution modeling. Converting plateaus to paddy and orchards significantly altered microhabitat availability by reducing the rock pool habitat availability in paddy and orchards, and increased deep, water-submerged areas and grass cover in paddy. Conversion to paddy mostly had species- and community-level impacts, that is, lowered species occurrence of certain species, lowered species richness, and more nested communities, whereas conversion to orchards mostly had species-level impacts, that is, lowered species occurrence, highlighting that different forms of agriculture have varying impacts on amphibians that can be determined by examining community- and species-level effects simultaneously. Using only community- or species-level metrics would not have unraveled these impacts completely. We show that large rock pools are critical microhabitats for frogs, most likely serving as refugia and protecting frogs from desiccation during dry spells in monsoons. Since Indian lateritic plateau habitats in low elevations are rapidly being converted to orchards, efforts are needed to conserve them in partnership with local communities, the custodians of these habitats.

A six-year ecotoxicological assessment of the Doce river and coastal marine areas impacted by the Fundão tailings dam failure, Brazil.

Physical factors that may account for regional patterns of plant species diversity remain controversial. We aim to determine the relationship of tree species diversity to environmental factors identifiable at regional scale in the northern Neotropics. We use a high‐resolution data set based on herbarium collections of all native tree species known to occur in the highly diverse and physiographically heterogeneous Mexican state of Chiapas. We analyzed 114 grid cells (5 min latitude×5 min longitude each) with 40 or more vouchers. We obtained from maps (scale 1:250 000) data on temperature, rainfall, elevation, and soils, and calculated for each grid cell mean actual evapotranspiration (AET), its ratio during the rainy and dry seasons (RET), average fertility/quality of soils (SFQ), and elevation (coarse‐scale topography) variance (SDE). These variables were largely independent of each other, and were entered in multiple regression models to predict species diversity assessed with Simpson's index of concentration. A model that accounted for 41.4% of the total variance in tree diversity showed positive effects of AET and seasonality (RET), whereas SFQ had a negative effect. A curvilinear model described well the relationship between tree diversity and AET (R 2 =0.45), and an intermediate maximum was detected. The data pattern suggested an asymptotic relationship as well, which was confirmed with a two‐part regression. Regression quantiles provided better estimates of the effect of SFQ with the upper envelope of the data (0.85–0.90 quantiles). Minimum diversity at intermediate rainfall values hints at a bimodal model of tree diversity along a rainfall gradient, in opposition to the frequent contention of a positive linear relationship. We suggest that broad‐scale climatic gradients interact with intraregional landscape‐level influences, thus leading to the observed nonlinear responses of tree diversity to environmental predictors.

The 2015-2016 El Niño led to historically high temperatures and low precipitation over the tropics, while the growth rate of atmospheric carbon dioxide (CO2) was the largest on record. Here we quantify the response of tropical net biosphere exchange, gross primary production, biomass burning, and respiration to these climate anomalies by assimilating column CO2, solar-induced chlorophyll fluorescence, and carbon monoxide observations from multiple satellites. Relative to the 2011 La Niña, the pantropical biosphere released 2.5 ± 0.34 gigatons more carbon into the atmosphere in 2015, consisting of approximately even contributions from three tropical continents but dominated by diverse carbon exchange processes. The heterogeneity of the carbon-exchange processes indicated here challenges previous studies that suggested that a single dominant process determines carbon cycle interannual variability.