Assemblage Structure Research Articles

Spatio-temporal variability of mesozooplankton distribution along the Canary Current Large Marine Ecosystem: a regional perspective.

The Canary Current Large Marine Ecosystem (CCLME), extending from Cape Spartel in Morocco to Guinea-Bissau, supports high primary and fisheries productivity driven by permanent or seasonal upwelling activity. During the current study, mesozooplankton and hydrographic sampling were conducted across the CCLME in the spring/summer of 2017 and the autumn/winter of 2019. The total mesozooplankton abundance and dry weight were found to be higher in 2017, partly due to the summer reproduction cycle of diplostracans. A prominent latitudinal gradient was observed in both the mesozooplankton standing stock and assemblage structure closely linked to a significant shift in oceanographic regimes at Cape Blanc (21°N). The area south of Cape Blanc, sampled during the upwelling relaxation in both years, was occupied by warmer South Atlantic Central Waters showing elevated mesozooplankton stock with a tropical assemblage structure. In contrast, cooler and more saline waters north of Cape Blanc, a result of the upwelling regime in that area, explained part of the observed variation in mesozooplankton composition among subregions and sampling periods. Our findings indicate that aside from the upwelling activity, spatiotemporal variation of mesoscale processes and topographical features at a subregional level may also shape mesozooplankton stock and assemblage structure in the CCLME.

Coupling between landward and seaward fringes of sandy beaches: algal deposits on the upper beach influence biogeochemistry and faunal assemblages in the swash zone

Energy subsidies from the sea typically underpin ocean-exposed sandy beach ecosystems. Strandings of detached macroalgae – ‘wrack’ – can be a spectacular form of such cross-ecosystem transfers of organic matter that sustain consumers in the recipient shore system; this has given rise to a model of wrack promoting the diversity and abundance of invertebrates, with scaling effects on upper trophic levels.However, most wrack is often wave-cast to the upper beach, whereas a distinct part of the shore fauna is limited to the ocean fringe of beaches – the ‘swash zone’. This has the potential to create a spatial asymmetry between the location of subsidies (concentrated at the landwards fringe) and the location of some of the putative recipients distributed at the ocean fringe.Here, we tested whether the fauna of the swash zone can benefit from wrack subsidies, by sampling fauna and algal deposits on a range of beaches in NW Spain. We also measured the potential functional link between algal wrack and nutrients released from wrack during decay.Wrack decay increased nutrient concentrations, and it is the combination of wrack cover, nutrient levels, and sediment coarseness that jointly drove variation in the assemblage structure of the swash fauna among beaches. Similarly, the density of the swash fauna and species richness increased markedly at higher nutrient levels and wrack cover.Filter feeders were an important compartment in the food web of the swash macrofauna; we hypothesize that wrack deposits in the upper beach enhance food availability for this trophic guild via increasing nutrients in the water column, stimulating primary production and providing particulate organic matter derived from algal decay. Besides, several polychaetes and peracarid species function as secondary consumers and detritus feeders that plausibly benefit, directly or indirectly, on the particulate organic matter that accumulates on the sediment surface or percolates into the interstitial environment.These findings expand the ‘wrack enhancement’ model to include the promotion of consumers at the ocean edge of sandy shores; it also contains a cross-shore linkage via decomposition processes that favourably change the nutrient regime across all the beach face and thereby couple the swash zone with the upper strandline.

Longitudinal and temporal variation in fish assemblage structure along lowland prairie Neotropical streams and relationships with environmental variables

The structure of fish assemblages in lotic systems usually varies from headwaters to the mouth, related to geomorphological and physicochemical changes. We evaluated the main processes that structure the fish assemblages on spatial, seasonal, and decadal (2009-2010; 2019-2020) scales and relationships with environmental variables in two low-impacted Neotropical Pampean streams tributaries to the Río de la Plata estuary (RdlP). Environmental variables related to the longitudinal variation in the fish assemblage were depth, macrophyte cover, and altitude, showing higher values in the headwater streams compared to downstreams. Species richness increased towards lower stream sectors due to the migration of riverine species from the RdlP. Beta diversity partitioning analysis showed that the greatest proportion of variability was explained by the turnover component in both the longitudinal and seasonal analyses. The headwater streams showed a more stable composition, consisting of species of the order Characiformes associated with aquatic macrophytes, while the downstream streams recorded greater variability due to the entry of migrant Siluriformes from the RdlP, highlighting the essential ecological function of Pampean streams for RldP fish assemblages. The decadal comparison showed that the longitudinal structure is persistent in the long term regardless of the study period. Therefore, the consistent pattern of longitudinal variation in fish assemblages and its explanatory variables have applicability in the conservation and biomonitoring of lowland streams, serving as reference for recovery efforts.

Ecological communities in white‐sand Amazonian rainforests are sensitive to deforestation—A dung beetle case

Abstract Campinarana is a fragile white‐sand rainforest ecosystem in Amazonia, where mining activities have been an important driver of landscape transformation, threatening biodiversity. Despite its importance for biodiversity, few studies have investigated insects' response to environmental disturbance in campinaranas. Here, we assess the differences between the dung beetle assemblages of undisturbed and disturbed campinaranas. The studied campinaranas differ substantially in their vegetation structure, the disturbed one strongly affected by mining activities. Dung beetle taxonomic diversity, abundance, biomass, and assemblage structure (species' distribution and relative abundances) from total and functional group perspective and indicator species were recorded in undisturbed and disturbed campinaranas. A total of 1592 beetles belonging to 42 species were collected in undisturbed campinaranas and 459 beetles from 11 species in disturbed campinaranas. Undisturbed campinaranas encompassed higher diversity, abundance, number of indicator species, and biomass, and their assemblages' structure were distinct from disturbed campinaranas. The abundance of roller dung beetles was the only parameter that was not affected by habitat type. Our results suggest that undisturbed campinaranas host sensitive ecological communities, with most of the species unable to cope with the changes brought by mining activities. In addition, dung beetle species can be a useful indicator for monitoring environmental disturbance in campinaranas. Considering the extension of the latter across the Amazon, this study provides information to support public policies to mitigate losses caused by deforestation in this hyperdiverse area.

Understanding fish assemblage structure using enviro assessment techniques in a Northwestern Himalayan reservoir of Beas River basin in Himachal Pradesh (H.P.), India.

Environmental factors play a fundamental role in shaping fish assemblage in aquatic ecosystems. The present study describes the fish assemblage structure on the spatial scale in Pong Reservoir, which lies in foothills of the Northwestern Himalaya within the river Beas basin. Through sophisticated enviro assessment techniques, using ArcGIS mapping, this study provides valuable insight into how physicochemical factors shape the fish assemblage in the reservoir. In total, 1211 individuals belonging to 8 orders, 10 families, 15 genera, and 19 species were recorded. The order Cypriniformes has the highest number of species. The invasive species Oreochromis niloticus was also documented for the first time in this reservoir. At a spatial scale, diversity indices reveal that the lacustrine zone had the lowest fish diversity. The transitional zone showed more species richness as compared to other riverine and lacustrine. The IUCN conservation status showed that among 19 fish species, two species (Wallago attu and Cyprinus carpio) are under vulnerable and only one species, Tor putitora, is under the endangered category. The majority of recorded water quality parameters fell within the acceptable range. CCA analysis of physiochemical parameters with fish abundance reveals that DO and turbidity were found to positively influence the species abundance. These findings provide a valuable resource for understanding ecology and also lay a solid foundation for the development of effective fisheries management strategies in this reservoir.

Temporal interactions among carnivores in an anthropized landscape of the coastal mountain range in southern Chile

Abstract The structuring of carnivore assemblages is based on the partitioning of niche axes, where the activity pattern is relevant for their coexistence. However, the continuous degradation of habitats, and the human presence (and exotic species) limit the availability of resources. Therefore, these species must readjust their requirements to minimize interactions derived from competition. For two years, activity patterns of two native carnivores (the cougar Puma concolor and the chilla fox Lycalopex griseus), one exotic carnivore (the domestic dog Canis lupus familiaris) and people were evaluated in an anthropogenic landscape in southern Chile. A differentiation was observed in the circadian cycle of the species, where the fox was predominantly nocturnal, while the cougar maintained a random activity pattern, in contrast to the dog and humans, which were the most diurnal. The ecological implications derived from the observed patterns are discussed, mainly in relation to the interference exerted by the exotic species.

Negative Impacts of Anthropogenic Disturbances on the Community Structure of Dung Beetles (Coleoptera: Scarabaeidae: Scarabaeinae) in Namibia.

Dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae) are a distinctive group of insects that are specialized in utilizing mammalian dung. They play a critical role in the ecosystem by decomposing dung, dispersing seeds, suppressing parasites, and cycling nutrients. Anthropogenic activities such as agriculture, land modification, fragmentation, road construction, and desertification have threatened dung beetles despite their roles in the ecosystem. Anthropogenic activities have a negative effect on dung beetle species diversity and composition. Namibia has been experiencing different types of land degradation, such as soil erosion, deforestation, bush encroachment, land conversion through agricultural activities, and sand mining, which have a greater effect on the species diversity and structure of dung beetles. In Namibia, there is a gap in quantitative research on the impact of anthropogenic activities on dung beetles; such a database is crucial for conservation purposes. Researchers have extensively used dung beetles to evaluate the assemblage structure, ecosystem function, and taxonomy of biodiversity.

Responses of fish to nationwide improvements in the water quality of a densely populated and heavily modified country over four decades.

Globally, fish have been severely affected by the widespread, chronic degradation of fresh waters, with a substantial proportion of species declining in abundance or range in recent decades. This has especially been the case in densely populated countries with an industrial heritage and intensive agriculture, where the majority of river catchments have been affected by deteriorations in water quality and changes in land use. This study used a spatially and temporally extensive dataset, encompassing 16,124 surveys at 1180 sites representing a wide range of river typologies and pressures, to examine changes in the fish populations of England's rivers over four decades (1980s-2010s). The analyses revealed gradual, nationwide increases in mean fish species richness and diversity across the range of pressure gradients. In the majority of cases, increases were most pronounced in the 1980s, since when any further changes have been comparatively minor, but there were no declining trends across the full time series. There were also temporal, nationwide changes in fish assemblage structure, driven largely by variations in the densities of brown trout Salmo trutta or roach Rutilus rutilus, but no consistent increases in the abundance of sensitive, pollution-intolerant species in response to improvements in wastewater treatment and, consequently, water quality. Although the increases in fish species richness and diversity over the last four decades are encouraging, subtle and contrasting changes in the abundance of a range of species require further investigation, and causal relationships between fish assemblage structure and putative drivers should be modelled at a national scale. This study is the first to examine long-term, nationwide trends in the freshwater fish populations of England, and significantly advances our understanding of the ecological health of rivers in densely populated and heavily modified countries.

Bird assemblage structure in the Desert Puna in areas with different disturbance activity of a subterranean herbivorous rodent

Bird assemblage structure in the Desert Puna in areas with different disturbance activity of a subterranean herbivorous rodent

Salinisation effects on benthic invertebrate assemblages in shallow lakes in arid and semiarid climate zones.

Shallow lakes, including those located at the border between Europe and Asia (Kazakhstan), have become very prone to increasing salinity because of climate change. Most of the study area is in one of the fastest-warming parts of the globe. Our research, conducted in four lakes varying in water salinity level and located in western Kazakhstan in the steppe, semi-desert, and desert zones, can be used to predict biodiversity as indicators of the natural potential of ecosystems. This was achieved by assessing the associations of invertebrate communities with environmental conditions based on data collected during nine seasonal measurement campaigns (in May, July, and September of 2019, 2020, and 2021). The multidimensional scaling (nMDS) of biotic and abiotic data enabled us to identify lakes as freshwater (1), oligohaline (1), and mesohaline (2). The key classifier was biotope salinity, irrespective of lake location in the steppe, semi-desert, or desert zones. Twenty-nine taxa were identified in the freshwater lake, 37 in the oligohaline, and 24-28 in the mesohaline lake; these accounted for ~ 80% of their estimated taxonomic composition, according to Species Accumulation Curves (SAC). The differences in the structure of benthic invertebrate assemblages revealed between the lakes are mainly concerned with the density and, to a lesser extent, the diversity of communities (Simpson index). As the salinity of the waters increased, the proportion of Diptera larvae significantly increased, and that of Ephemeroptera larvae decreased. Sigara assimilis, accompanied by Sphaeromas sp., Chironomus sp., and Saeharia sp., proved strongly resistant to increased water salinity. Among the studied lakes, the semi-desert lake Balykty Sarkyl (β-mesohaline) is strongly threatened by biodiversity degradation due to unfavourable climatic conditions. Time series analysis for Lake Edilsor (α-mesohaline) shows that it underwent the most rapid salinisation, which has increased the number of taxa tolerant to this predictor (mainly Diptera larvae). The results confirm that detailed taxonomic assessment (including time series) can significantly improve our understanding of lake changes with increasing salinity caused by climate change and/or other stressors.

Variation of functional diversity structure measured as combined species dominance, functional diversity, and functional redundancy in two taxa of ectoparasitic arthropods at two spatial scales: host-associated, ecological, and geographic effects.

The functional diversity structure of a community can be represented as a combination of three additive components (species dominance D, functional redundancy R, and functional diversity Q) (DRQ approach in which different facets of functional differences between species are considered simultaneously). We applied this concept to assemblages of fleas and gamasid mites parasitic on small mammals at continental (across regions of the Palearctic) and regional (across sampling sites in Slovakia) scales and asked: What are the relative effects of host species, biome/habitat type, and geographic locality on the DRQ composition of a parasite assemblage? At the continental scale, regions were partitioned according to predominant biome or geographic position in a continental section. At the regional scale, sampling sites were partitioned according to habitat type or geographic locality. We tested for differences in the functional diversity structure (measured as the DRQ composition) of an ectoparasite assemblage (a) within a host species between biomes/habitat types or continental sections/localities and (b) between host species within a biome/habitat type or a continental section/locality. At both scales, the functional diversity structure of both flea and mite assemblages differed mainly between host species within a biome/habitat or geographic regions/locations, whereas differences in the DRQ composition between biomes/habitats or geographic regions/locations were only detected in a few host species. We compare our results with the results of earlier studies and conclude that the DRQ approach has an advantage over a single diversity metric and allows a better understanding of spatial variation in different facets of ectoparasite diversity.

Fish associated with microhabitats of submerged fallen logs in a lake in the Brazilian Amazon

Microhabitats represent an important factor for fish survival, providing food and shelter, in addition to good temperature conditions and dissolved oxygen levels. One of these temporary microhabitats formed is that of submerged logs, which, due to the flooding of adjacent areas, become available for fish. In this sense, the present study evaluates the composition and structure of fish assemblages associated with submerged logs on the banks of an Amazonian lake and identified the diversity of species according to the hydrological period. Field work was carried out on the banks of Tupé lake, in the lower Negro River, using scoop nets. The sampling was carried out in an area which measured 16 m² (4 m x 4 m) and, within this area, the effort was standardized with the presence of three researchers fishing for approximately one hour in each of the sampling sites. The capture of the fish was carried out with the aid of hand nets (“puçá” and “rapiché”) and sieve. Absolute abundance (N), richness (S), Shannon-Wiener diversity index (H'), Berger Parker dominance (d) and equitability (E) were analyzed. Analysis of variance (p <0.05) was used to verify the temporal variation. A total of 631 specimens were captured, which were distributed in eight families and 25 species, with the orders of Characiformes (67.8%) and Cyprinodontiformes (22.8%) predominating. In the high water period, the highest values of numerical abundance and dominance were observed, while in the low water period, the highest values of species diversity, richness and equitability were found. Therefore, the results presented here can serve as a basis for fisheries management, as well as for conservation measures in these environments that help to maintain fish assemblages.

Bat Cutaneous Microbial Assemblage Functional Redundancy Across a Host-Mediated Disturbance

Understanding the processes and factors that influence the structure of host-associated microbial assemblages has been a major area of research as these assemblages play a role in host defense against pathogens. Previous work has found that bacterial taxa within bat cutaneous microbial assemblages have antifungal capabilities against the emerging fungal pathogen, Pseudogymnoascus destructans. However, our understanding of natural fluctuations in these cutaneous microbial assemblages over time due to shifts in host habitat is lacking. The objective of this work was to understand how the taxonomic and functional bat cutaneous microbial assemblage responds to seasonal shifts in host habitat. We hypothesized that at the community level, there will be turnover in taxonomic structure but functional redundancy across seasons. On a finer scale, we hypothesized that there will be differences in the relative abundance of functional genes that code for select pathways across seasons. Results showed that, on a broad scale, the bat cutaneous microbial assemblage is seasonally taxonomically dynamic but functionally redundant. Additionally, although there was almost complete taxonomic turnover between winter and summer bat microbial assemblages, there was no difference in assemblage structure across winters. This functional redundancy was also observed at finer scales, with no differences in the abundance of genes within pathways of hypothesized importance across seasons or winters. Taken together, results suggest species sorting mechanisms correlated with shifts in host habitat use, drive taxonomic but not functional host-associated cutaneous microbial community assembly.

Threshold responses of freshwater fish community size spectra to invasive species

AbstractAquatic invasive species (AIS) threaten biodiversity and ecosystem services around the world, but their management has been hampered by the lack of quantifiable control targets. The introduction of Silver Carp (Hypophthalmichthys molitrix) throughout the mid‐western United States epitomizes both the impacts of AIS and the need for quantitative control targets. Silver Carp are large‐bodied planktivores that compete with native planktivores, which can cause cascading effects throughout the food web. Our study tested the threshold of abundance beyond which Silver Carp alter fish assemblage structure. We used a community size spectra (CSS) approach to evaluate fish community size structure across temporal and spatial gradients of Silver Carp abundances. We hypothesized that Silver Carp would flatten the size spectra slope because they are large‐bodied and feed at a low trophic position. Electrofishing data were obtained for the La Grange Pool of the Illinois River (1994–2021) and for six pools of the Ohio River (2015–2020). Results supported our hypothesis, showing a 98% probability that the relative biomass of Silver Carp is positively related to the CSS slope (resulting in “flattening”). This pattern was strongest in the Illinois River, where Silver Carp made up >30% of fish assemblage biomass in recent years. The pattern was weakest in the Ohio River (78% probability of a positive relationship) where Silver Carp rarely exceeded 20% of total fish biomass. Subsequent changepoint models indicated that a Silver Carp relative biomass of ~24% represents a threshold below which negative food web impacts should be minimized. Our study demonstrates a clear shift in fish community size structure following invasion by Silver Carp and suggests that pre‐invasion CSS slopes may serve as a restoration target. It also illustrates the benefits of CSS to guide Silver Carp and other AIS management.

Estuarine lateral ecotones shape taxonomic and functional structure of fish assemblages. The case of the Seine Estuary, France

Estuaries are complex ecotones including multiple lateral habitats that play essential functions for fish assemblages. However, the distribution of fish diversity and community assembly processes remain poorly documented in these habitats. This paper investigated the taxonomic and functional diversities of fish assemblages along lateral continuums of three salinity areas over the longitudinal gradient of the Seine Estuary. We examined fish diversity at a local scale (⍺-diversity) and between local scales (β-diversity) across the lateral habitats (estuarine main channel, tidal marsh, and diked marsh). Overall, the taxonomic diversity follows a typical ecotone distribution, with the highest richness reported at the system margins and high species dissimilarity between communities. The decrease of functional diversity in upper part of the lateral ecotone probably reflects the homogenisation of ecological niches. Changes in assembly processes between the three salinity conditions suggests that several lateral ecotones occur in estuaries with complementary functions for fish assemblages.

Elasmobranch assemblage structure on protected high-latitude coral reefs of southeast Africa

High-latitude coral reefs (HLCRs) are unique ecosystems with diverse biological assemblages, including many low latitude species on their distribution margins. These ecosystems are threatened by fisheries exploitation, habitat destruction and climate change; however, relative to low latitude coral ecosystems, our understanding of their structure and functioning is limited. This is particularly true for sharks and rays. In this study, we used baited remote underwater stereo-video systems to determine the effect of habitat and management on the assemblage structure of elasmobranchs on the HLCRs of southern Africa (26-28°S; iSimangaliso Marine Protected Area [MPA], South Africa, and the adjoining Ponta do Ouro Partial Marine Reserve, Mozambique). We recorded a total of 12 species of shark (142 individuals) and 9 species of ray (40 individuals) over 2 brief time frames (November 2016 and June 2017). All species were tropical with many on the southern limit of their known distributions. Sharks increased in diversity with depth and showed a preference for the reef and mosaic habitats, relative to sand. The occurrence of rays was predominantly influenced by the presence of low relief habitats. These findings highlight the need for MPAs to encompass both sand and reef habitats over broad depth ranges to effectively protect elasmobranch assemblages. We found evidence to support the high average abundance and diversity of sharks and rays within MPAs of South Africa and southern Mozambique. The results highlight the importance of marginal HLCRs, particularly those within MPAs, for the management and conservation of tropical elasmobranch species.

Climatic seasonality and dominant species drive the temporal dynamics in a lizard assemblage in the Arid Chaco - Monte ecotone

Lizard assemblages are dynamic, influenced by both seasonal climatic changes and intrinsic population shifts. Climate plays a crucial role in shaping lizard phenology, or the timing of their biological events, which critically affects the spatiotemporal structure of sympatric populations. Understanding how species richness and abundance fluctuate over time, and how these changes are influences by temporal factors, is essential for distinguishing between variations caused by unpredictable external factors and underlying natural changes. This study aimed to characterize lizard assemblage structure and dynamics, as well as species demographics, over three consecutive years within an Arid Chaco - Monte ecotone in central-western Argentina. We also sought to assess the effects of environmental drivers (e.g., temperature, precipitation) on assemblage and population dynamics. Monthly samples were taken using pitfall traps from October 2015 to May 2018 within the protected area of the Valle Fértil Multiple Use Reserve. We captured 1446 lizards, representing 12 species. Liolaemus chacoensis was dominant in the assemblage, followed by Teius teyou and Aurivela longicauda. Species richness and diversity varied seasonally, peaking during summer and autumn. The lizard assemblage exhibited activity throughout all seasons, with significant temporal niche overlap between species. Reproduction and activity in lizards were highly seasonal, primarily occurring in spring and summer, likely due to low winter temperatures and highly seasonal rainfall. Our study shows that climate seasonality and the demographics of the dominant species significantly influence the temporal dynamics of lizard assemblages in the Arid Chaco-Monte ecotone of Argentina.

Fish assemblage structure and functional guild composition of Matla Estuary, Indian Sundarbans

Fish assemblage structure and functional guild composition of Matla Estuary, Indian Sundarbans

Small hydropower dam alters the functional structure of macroinvertebrate assemblages in a Neotropical savanna river

Small hydropower dam alters the functional structure of macroinvertebrate assemblages in a Neotropical savanna river

Latitudinal Patterns and Macroclimatic Drivers of Phylogenetic Structure in Regional Liverwort Assemblages in North America

ABSTRACTAimMost plant groups originated under tropical conditions, leading to the hypothesis of tropical niche conservatism, according to which species assemblages of a clade originating and diversifying in tropical climates are expected to have low phylogenetic diversity and dispersion in temperate climates because only few lineages have adapted to these novel conditions. The opposite may be expected for clades originating under temperate conditions, but this temperate niche conservatism hypothesis has not been tested for a broad temperature gradient including both tropical and arctic climates. Liverworts are thought to have originated in temperate climates, and may thus follow the pattern of temperate niche conservatism. Here, we test this hypothesis using regional liverwort floras across a nearly full temperature gradient from tropical through temperate to arctic climates in North America. In addition, we investigate whether temperature‐related variables and climate extreme variables play a more important role in determining phylogenetic structure of liverwort assemblages, compared to precipitation‐related variables and climate seasonality variables, respectively.LocationNorth America.TaxonLiverworts (Marchantiophyta).MethodsPhylogenetic diversity (measured as mean pairwise distance) and phylogenetic dispersion (measured as standardised effect size of mean pairwise distance) in liverworts in regional floras in North America were related to latitude and climatic variables. Variation partitioning analysis was used to assess the relative importance of temperature‐ versus precipitation‐related variables and of climate extremes versus seasonality on phylogenetic diversity and dispersion.ResultsPhylogenetic diversity and dispersion in liverworts is highest in temperate climates, compared to both tropical and arctic climates. Temperature‐related variables and climate extreme variables explained more variation in phylogenetic diversity and dispersion of liverwort assemblages than did precipitation‐related variables and climate seasonality variables, respectively.Main ConclusionsVariations in phylogenetic diversity and dispersion in liverworts along the latitudinal gradient in North America are consistent with the temperate niche conservatism hypothesis.