A reliable description of any spatial pattern in species richness requires accurate knowledge about species geographical distribution. However, sampling bias may generate artefactual absences within ...species range and compromise our capacity to describe biodiversity patterns. Here, we analysed the spatial distribution of 35,000 marine species (varying from copepods to sharks) to identify missing occurrences (gaps) across their latitudinal range. We find a latitudinal gradient of species absence peaking near the equator, a pattern observed in both shallow and deep waters. The tropical gap in species distribution seems a consequence of reduced sampling effort at low latitudes. Overall, our results suggest that spatial gaps in species distribution are the main cause of the bimodal pattern of marine diversity. Therefore, only increasing sampling effort at low latitudes will reveal if the absence of species in the tropics, and the consequent dip in species richness, are artefacts of sampling bias or a natural phenomenon.
Environmental filtering is a major mechanism structuring ecological communities. However, it is still not clear how different abiotic drivers composing the environmental filter interact with each ...other to determine local species assemblage and create spatial patterns in species distribution. Here, we evaluated the effects of two strong and uncorrelated environmental variables (salinity and sediment properties) on the β-diversity of an estuarine macrobenthic community while accounting for spatial effects. Our results show that the benthic community composition has a strong spatial structure along the estuary, which can be greatly explained by salinity and sediment variation. Salinity is most associated with species replacement (turnover), whereas sediment is more important for species loss (nestedness). However, the effects of sediment variation on nestedness are mainly detected at a smaller spatial scale (estuarine sectors), whereas the effects of salinity on species turnover are stronger as spatial scale increases (entire estuary). Our findings suggest that environmental filters can drive both turnover and nestedness components of β-diversity, but that their relative importance depends on the spatial scale of investigation. Although abiotic drivers associated with detrimental effects (sediment) usually result in nestedness, larger spatial scales encompass abiotic drivers associated with different suitable conditions (salinity), increasing the relative importance of the replacement component of species β-diversity.
Although octocorals are a key component of marine hard-bottom systems, their feeding performance is still poorly understood. Understanding carbon budget trends in octocorals’ feeding ecology seems ...essential to assess their role in benthic–pelagic coupling and to predict their responses to environmental changes. Herein, we provide a review of the feeding ecology of octocorals and an overall data reassessment of their carbon budgets through a systematic and comprehensive search of peer-reviewed literature published between 1960 and 2020, highlighting knowledge gaps. Overall, the feeding ecology of more than 95% of octocoral species remains unknown. Based on the available data, suspension feeding accounts for 162.8 ± 171.0% of the metabolic requirements in azooxanthellate octocorals and 28.7 ± 32.3% in zooxanthellate octocorals. Autotrophy is responsible for 156.7 ± 113.9% of the acquired carbon in zooxanthellate octocorals. However, this value is significantly lower in gorgonian phenotypes compared to other soft corals. We present a conceptual framework describing and exploring the most relevant hypotheses regarding putative advantages of octocorals over scleractinians against environmental changes, including their ability to decrease energy expenses to overcome stress events, their lower dependency on autotrophy, and the type of interaction (facultative and flexible) with their symbionts.
Marine plastic debris provides a significant surface area for potential colonization by planktonic and benthic harmful microalgae and for the adsorption of their toxins. Furthermore, floating ...plastics may substantially expand the substrate area available for benthic algae in the ocean, intensifying the transfer of potent toxins through pelagic food webs. In this study, we quantify the available surface area of micro- and macroplastics in different oceanic regions and assess the potential role of floating plastics as vectors for the transfer of toxins from three widespread benthic dinoflagellates, Gambierdiscus spp., Ostreopsis cf. ovata and Prorocentrum lima. To avoid bias associated to the occurrence of benthic algae in deep waters, we selected only records from 0 to 100 m depths. We estimate that 26.8 × 1010 cm2 of plastic surface area is potentially available in surface waters of the global ocean, mostly in the size range of large microplastics (1.01–4.75 mm). Based on the distribution of floating plastics and the habitat suitability of the selected microalgal species, the plastic relative colonization risks will be greater in the Mediterranean Sea and in the subtropical and temperate western margins of the oceans, such as the North American and Asian eastern coasts and, to a lesser extent, southern Brazil and Australia. In places where the colonization of O. cf. ovata cells on floating plastic debris has been properly quantified, such as the Mediterranean and southern Brazil, we estimate a colonization potential of up to 2 × 106 cells km−2 of ocean surface during the regular occurrence period and up to 1.7 × 108 cells km−2 during massive blooms of this species. As plastic pollution and harmful benthic algal blooms have both increased substantially over the past decades, we suggest that their interactive effects can become a major and novel threat to marine ecosystems and human health.
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•Plastic debris are novel substrates for harmful algae in the ocean.•Integrating available plastic area and algae suitability maps indicate regions under risk.•Risk of colonization by benthic algae is greater in subtropical and temperate regions.•Plastics can facilitate the dispersal of benthic toxic algae from the tropics to higher latitudes.
Aim
The decreasing capacity of area to predict species richness on small islands (the small‐island effect; SIE) seems to be one of the few exceptions of the species–area relationship. While most ...studies have focused on how to detect the SIE, the underlying ecological factors determining this pattern remain largely unexplored. Here, we evaluate one of the few mechanisms proposed to explain the SIE, the subsidized island biogeography hypothesis, which posits that marine productivity around small islands may alter their expected species richness.
Location
Seven hundred and ninety islands worldwide, including 420 islands < 1 km2.
Time period
Present.
Major taxa studied
Angiosperms.
Methods
We applied iterative partial regression to determine the effects of island area and marine productivity on plant species richness for islands of varying sizes. We also employed geographically weighted regression to account for non‐stationarity in the marine productivity effects. Lastly, we used estimates of ammonia emissions based on nutrient excretion by seabird colonies from a subset of 66 islands to evaluate the effects of marine resources deposition on angiosperm species richness.
Results
We found no effect of marine productivity on insular species richness, at both regional and global scales. In all models, area emerged as the only predictor of plant species richness. A weak contribution of marine productivity was only detectable in models with a low number of islands, but this effect was independent of island size. Although nutrient deposition significantly contributes to explaining plant diversity, this effect was also independent of island size.
Main conclusions
Our study demonstrates that marine productivity has no general effect on plant species richness of small islands worldwide. Although marine‐derived resources may still contribute to species richness variation, this effect does not seem to be restricted to small islands. Overall, our results do not provide support for the subsidized island biogeography hypothesis.
The latitudinal diversity gradient (LDG) has been investigated for decades, with hundreds of studies focusing on different organisms, regions and habitat types. Meta‐analysis may be considered, ...therefore, a useful tool to explore the generality and limitations of this remarkable macroecological pattern. The first meta‐analysis exploring variations in the LDG, published by Hillebrand in 2004, revealed that the latitudinal decline in species richness seems to be indeed a general phenomenon. However, Kinlock et al. (2018, Global Ecology and Biogeography, 27, 125–141) revisited recently the challenge of synthesizing individual LDGs and indicated that the phenomenon is not ubiquitous among habitats of the marine realm. More precisely, they indicated that the phenomenon is non‐significant in the benthic habitat. Here, we suggest that the marine habitat categories used by them (i.e., benthic, coral reefs, coastal, open ocean) are not independent and that reclassifying the studies significantly alters one of their main results. By assigning the studies into benthic and pelagic categories, and additionally into coastal or oceanic zones, we show that non‐ambiguous, evolutionarily meaningful marine habitats display a significant latitudinal decline in species richness.
Landscape dynamics are widely thought to govern the tempo and mode of continental radiations, yet the effects of river network rearrangements on dispersal and lineage diversification remain poorly ...understood. We integrated an unprecedented occurrence dataset of 4,967 species with a newly compiled, time-calibrated phylogeny of South American freshwater fishes-the most species-rich continental vertebrate fauna on Earth-to track the evolutionary processes associated with hydrogeographic events over 100 Ma. Net lineage diversification was heterogeneous through time, across space, and among clades. Five abrupt shifts in net diversification rates occurred during the Paleogene and Miocene (between 30 and 7 Ma) in association with major landscape evolution events. Net diversification accelerated from the Miocene to the Recent (c. 20 to 0 Ma), with Western Amazonia having the highest rates of in situ diversification, which led to it being an important source of species dispersing to other regions. All regional biotic interchanges were associated with documented hydrogeographic events and the formation of biogeographic corridors, including the Early Miocene (c. 23 to 16 Ma) uplift of the Serra do Mar and Serra da Mantiqueira and the Late Miocene (c. 10 Ma) uplift of the Northern Andes and associated formation of the modern transcontinental Amazon River. The combination of high diversification rates and extensive biotic interchange associated with Western Amazonia yielded its extraordinary contemporary richness and phylogenetic endemism. Our results support the hypothesis that landscape dynamics, which shaped the history of drainage basin connections, strongly affected the assembly and diversification of basin-wide fish faunas.
Islands are biodiversity hotspots that host unique assemblages. However, a substantial proportion of island species are threatened and their long‐term survival is uncertain. Identifying and ...preserving vulnerable species has become a priority, but it is also essential to combine this information with other facets of biodiversity like functional diversity, to understand how future extinctions might affect ecosystem stability and functioning. Focusing on mammals, we (i) assessed how much functional space would be lost if threatened species go extinct, (ii) determined the minimum number of extinctions that would cause a significant functional loss, (iii) identified the characteristics (e.g., biotic, climatic, geographic, or orographic) of the islands most vulnerable to future changes in the functional space, and (iv) quantified how much of that potential functional loss would be offset by introduced species. Using trait information for 1474 mammal species occurring in 318 islands worldwide, we built trait probability density functions to quantify changes in functional richness and functional redundancy in each island if the mammals categorized by IUCN as threatened disappeared. We found that the extinction of threatened mammals would reduce the functional space in 63% of the assessed islands, although these extinctions in general would cause a reduction of less than 15% of their overall functional space. Also, on most islands, the extinction of just a few species would be sufficient to cause a significant loss of functional diversity. The potential functional loss would be higher on small, isolated, and/or species‐rich islands, and, in general, the functional space lost would not be offset by introduced species. Our results show that the preservation of native species and their ecological roles remains crucial for maintaining the current functioning of island ecosystems. Therefore, conservation measures considering functional diversity are imperative to safeguard the unique functional roles of threatened mammal species on islands.
Islands are home to unique assemblages that include a substantial proportion of threatened species. The aim of this study was to evaluate how potential future extinctions will affect islands functional space. We found that the extinction of threatened mammals would reduce the range of functional strategies of insular communities on most islands. This functional loss would be higher on small, isolated and/or species‐rich islands. It is further demonstrated that in general this loss would not be compensated by introduced species. These results suggest that the preservation of native species remains crucial for maintaining the current functioning of island ecosystems.
The productivity gradient between adjacent habitats can fluctuate over time due to seasonal cycles and lead to both habitats being alternately subsidized. Although this process is well known for prey ...subsidies in stream-riparian forest ecotones, few studies are available for other systems or subsidy types. Moreover, the effects of transport intensity on this expected alternate subsidy exchange are still poorly understood. We assessed whether subsidy input and allochthonous carbon assimilation by resident benthic invertebrates alternated between adjacent mangroves and salt marshes during peaks of detritus productivity (summer and winter, respectively) in a subtropical estuary, by using detritus trapping techniques and stable isotope ratios. Sampling was performed simultaneously in the sheltered (inner sector) and exposed (outer sector) regions of the estuary to assess the influence of different physical conditions on the intensity of subsidy flow. Transport of mangrove litter into the salt marsh occurred mainly in the summer in both sectors; however, most of the litter remained trapped in the marsh boundary. The mixing model also showed that there was little influence of allochthonous carbon in the diet of salt marsh benthic invertebrates. Marsh litter supply to mangroves did not vary significantly between seasons but was significantly higher in the outer than in the inner sector. Likewise, the mixing model showed great contribution of salt marsh carbon to the diet of benthic invertebrates from the outer-sector mangroves, whereas autochthonous carbon predominated in those from the inner mangroves. Our findings reinforce the model that trophic connectivity relies on the relative proportion of allochthonous (subsidy) and autochthonous resources rather than only on asymmetric productivity between habitats. Differences in the proportion of resources result from interaction among productivity, permeability, and transport vectors that lead to many states of trophic connectivity.
The mouth dynamics of temporarily open/closed estuaries (TOCEs) play a key role in their overall functioning. In this study, the effect of the inlet state (closed vs. artificially breached) on ...spatial variability of macrobenthic invertebrates (composition, abundance, and biomass) was assessed in a temporarily open/closed lagoon of South Brazil (28°35′S/48°52′W). Samplings were carried out in two periods during closed (July and November) and open phases (July and November). Additionally, in order to evaluate possible transitory effects of breaching, data obtained during closed and open phases were compared with those samples taken 60 days after the end of mechanical opening of the mouth (January). The artificial breaching markedly changed the dynamic of the benthic environment. After the inlet dredging and bulldozing, total organic content and microphytobenthic biomass were significantly reduced. The disturbance also resulted in a population crash of the macrobenthic invertebrates, with a reduction of 50% in biomass and 90% in density. Following the shock produced by the artificial breaching, most of the macroinvertebrates descriptors recovered, as shown by the univariate and multivariate analysis. However, a benthic community with a significantly different structure emerged. During the study, the macroinvertebrates from inner portions of the lagoon were less variable than those in the middle or near the lagoon inlet. The results of this study showed that the macrobenthic associations of Camacho lagoon were primarily structured by salinity and microphytobenthic biomass, which in turn, were regulated by the state of the inlet.
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