Intraspecific phenotypic variation in a fish predator affects multitrophic lake metacommunity structure

Contemporary insights from evolutionary ecology suggest that population divergence in ecologically important traits within predators can generate diversifying ecological selection on local community structure. Many studies acknowledging these effects of intraspecific variation assume that local populations are situated in communities that are unconnected to similar communities within a shared region. Recent work from metacommunity ecology suggests that species dispersal among communities can also influence species diversity and composition but can depend upon the relative importance of the local environment. Here, we study the relative effects of intraspecific phenotypic variation in a fish predator and spatial processes related to plankton species dispersal on multitrophic lake plankton metacommunity structure. Intraspecific diversification in foraging traits and residence time of the planktivorous fish alewife (Alosa pseudoharengus) among coastal lakes yields lake metacommunities supporting three lake types which differ in the phenotype and incidence of alewife: lakes with anadromous, landlocked, or no alewives. In coastal lakes, plankton community composition was attributed to dispersal versus local environmental predictors, including intraspecific variation in alewives. Local and beta diversity of zooplankton and phytoplankton was additionally measured in response to intraspecific variation in alewives. Zooplankton communities were structured by species sorting, with a strong influence of intraspecific variation in A. pseudoharengus. Intraspecific variation altered zooplankton species richness and beta diversity, where lake communities with landlocked alewives exhibited intermediate richness between lakes with anadromous alewives and without alewives, and greater community similarity. Phytoplankton diversity, in contrast, was highest in lakes with landlocked alewives. The results indicate that plankton dispersal in the region supplied a migrant pool that was strongly structured by intraspecific variation in alewives. This is one of the first studies to demonstrate that intraspecific phenotypic variation in a predator can maintain contrasting patterns of multitrophic diversity in metacommunities.     

Connectivity and cladoceran species richness in a metacommunity of shallow lakes

SUMMARY 1. The shallow ponds of the nature reserve 'De Maten' form a metacommunity, in which individual ponds are highly interconnected via a system of overflows and rivulets. This study reports on the relations between cladoceran species richness and (a) connectivity patterns and (b) local environmental variables.
2. No relation was found between local species richness and three connectivity variables or dispersal pathways.
3. Spatial configuration was related to richness, but was confounded by environmental variables for 2 of 3 years. In those 2 years, there was a significant linear relation between Secchi disc depth and species richness, suggesting an important impact of the clearwater/turbid state alternative equilibria in shallow lakes in determining cladoceran richness. Only in the year in which environmental variables were unimportant did connectivity between the ponds influence species richness.
4. These results suggest that local environmental variables related to the clearwater/turbid state alternative equilibria in shallow lakes are important in determining cladoceran species richness. Connectivity and dispersal of individuals between the different ponds only act secondarily by increasing the general species richness within a pond through dispersal from ponds with different environmental conditions.     

青海湖湿地鸭科鸟类群落结构

2007 ～2010年每年4～10月,采用直接计数法对青海湖周边6种典型生境包括河口湿地、湖泊、淡水沼泽、淡水泉、岩石湖岸、沙滩中的鸭科鸟类群落进行了调查.共记录到鸭科鸟类9属21种,采用频率指数法确定的优势种有斑头雁( Anser indicus)、赤麻鸭(Tadorna ferruginea)、针尾鸭(Anas a...     

Surface water connectivity drives richness and composition of Arctic lake fish assemblages

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Is the island biogeography model a poor predictor of biodiversity patterns in shallow lakes?

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The number of breeders explains genetic connectivity in an endangered bird

Connectivity is central to ecology and evolution as it focuses on the movement of individuals or genes across landscapes. Genetic connectivity approaches aim to understand gene flow but often estimate it indirectly based on metrics of genetic differentiation, which can also be affected by other evolutionary forces such as genetic drift. Gene flow and genetic drift are driven by separate ecological mechanisms with potentially differing effects on genetic differentiation and interpretations of genetic connectivity. The ecological mechanisms contributing to gene flow and genetic drift are primarily effective dispersal, or movement followed by successful reproduction, and the number of breeders in a local population, N_b, respectively. Yet, rarely are these ecological mechanisms and genetic connectivity measured simultaneously across landscapes. We examine the roles of effective dispersal and N_b on genetic connectivity across the entire range of the endangered snail kite (Rostrhamus sociabilis plumbeus), between 2006–2015. We find that both N_b and effective dispersal are important predictors of genetic connectivity across this landscape, but that N_b has a 3 × stronger effect on genetic connectivity. Furthermore, N_b is positively correlated with heterozygosity and allelic richness within patches, suggesting a potentially important role of genetic drift, in addition to gene flow, on genetic connectivity. These results emphasize that conservation efforts should focus on not only between‐patch processes of movement but also within‐patch processes regarding habitat quality and local population size for increasing genetic connectivity.     

Habitat quality of source patches and connectivity in fragmented landscapes

Because spatial connectivity is critical to dispersal success and persistence of species in highly fragmented landscapes, the way that we envision and measure connectivity is consequential for biodiversity conservation. Connectivity metrics used for predictive modeling of spatial turnover and patch occupancy for metapopulations, such as with Incidence Function Models (IFM), incorporate distances to and sizes of possible source populations. Here, our focus is on whether habitat quality of source patches also is considered in these connectivity metrics. We propose that effective areas (weighted by habitat quality) of source patches should be better surrogates for population size and dispersal potential compared to unadjusted patch areas. Our review of a representative sample of the literature revealed that only 12.5% of studies incorporated habitat quality of source patches into IFM-type connectivity metrics. Quality of source patches generally was not taken into account in studies even if habitat quality of focal patches was included in analyses. We provide an empirical example for a metapopulation of a rare wetland species, the round-tailed muskrat (Neofiber alleni), demonstrating that a connectivity metric based on effective areas of source patches better predicts patch colonization and occupancy than a metric that used simple patch areas. The ongoing integration of landscape ecology and metapopulation dynamics could be hastened by incorporating habitat quality of source patches into spatial connectivity metrics applied to species conservation in fragmented landscapes.     

Both landscape and local factors influence plant and hexapod communities of industrial water‐abstraction sites

1. At the landscape level, intensification of agriculture, fragmentation, and destruction of natural habitats are major causes of biodiversity loss that can be mitigated at small spatial scales. However, the complex relationships between human activities, landscapes, and biodiversity are poorly known. Yet, this knowledge could help private stakeholders managing seminatural areas to play a positive role in biodiversity conservation.
2. We investigated how water‐abstraction sites could sustain species diversity in vascular‐plant communities and two taxonomic groups of insect communities in a fragmented agricultural landscape.
3. Landscape‐scale variables (connectivity indices and surrounding levels of herbicide use), as well as site‐specific variables (soil type for vascular plants, floral availability for Rhopalocera, and low herbaceous cover for Orthoptera), were correlated to structural and functional metrics of species community diversity for these taxonomic groups, measured on 35 industrial sites in the Ile‐de‐France region in 2018–2019.
4. Rhopalocera and Orthoptera consisted essentially of species with a high degree of dispersal and low specialization, able to reach the habitat patches of the fragmented landscape of the study area. Sandy soil harbored more diverse vascular‐plant communities. Plant diversity was correlated to a greater abundance of Rhopalocera and a lower richness of Orthoptera.
5. Increasing landscape connectivity was related to higher abundance of plants and Rhopalocera, and a higher evenness index for Orthoptera communities. Higher levels of herbicide use were related to a decrease in the biodiversity of plants and Rhopalocera abundance. High levels of herbicide favored high‐dispersal generalist plants, while high levels of connectivity favored low‐dispersal plants. Specialist Orthoptera species were associated with low herbaceous cover and connectivity.
6. Water‐abstraction sites are valuable seminatural habitats for biodiversity. Changing intensive agricultural practices in surrounding areas would better contribute to conserving and restoring biodiversity on these sites.

     

Influence of sampling effort on metrics of fish-based indices for the assessment of estuarine ecological quality

Multimetric fish-based indices have been increasingly gaining importance in Europe, as the Water Framework Directive (WFD) requires fish fauna, and particularly its composition and abundance, to be taken into account in the assessment of the ecological quality of continental surface waters, including transitional waters. These indices are composed of several metrics, mostly related with structural and functional characteristics of fish communities, such as species richness, the role of nursery areas, or trophic web structure. Therefore, ecological quality assessments should ensure that these structural and functional characteristics of fish communities were covered by the sampling methods used. In the present work, the influence of sampling effort on several metrics of the Estuarine Fish Assessment Index (EFAI) was studied. Pseudo-random samples were generated from data of four Portuguese estuaries and bootstrap cycles were performed, in order to obtain metrics’ means and standard deviations per number of hauls analysed. The number of hauls necessary for the means to level off differed with the metrics considered. Generally, for metrics on percentages (percentage of marine migrants, percentage of estuarine residents and percentage of piscivores) the curve levelled off with less than 20 hauls, both for the estuary as a whole and for different estuarine salinity zones. On the other hand, metrics on species richness required much larger samples. In order to decrease to −5% the current estimated bias of metrics, the WFD sampling costs would have to be more than 3 times higher than they currently are. The findings in the present study are of great importance for an effective assessment of estuarine ecological quality and particularly in the context of the WFD, as the metrics studied are common to other Member State indices.     

The role of environmental and spatial processes in structuring native and non‐native fish communities across thousands of lakes

Quantifying the role of spatial patterns is an important goal in ecology to further understand patterns of community composition. We quantified the relative role of environmental conditions and regional spatial patterns that could be produced by environmental filtering and dispersal limitation on fish community composition for thousands of lakes. A database was assembled on fish community composition, lake morphology, water quality, climatic conditions, and hydrological connectivity for 9885 lakes in Ontario, Canada. We utilized a variation partitioning approach in conjunction with Moran's Eigenvector Maps (MEM) and Asymmetric Eigenvector Maps (AEM) to model spatial patterns that could be produced by human‐mediated and natural modes of dispersal. Across 9885 lakes and 100 fish species, environmental factors and spatial structure explained approximately 19% of the variation in fish community composition. Examining the proportional role of spatial structure and environmental conditions revealed that as much as 90% of the explained variation in native species assemblage composition is governed by environmental conditions. Conversely on average, 67% of the explained variation in non‐native assemblage composition can be related to human‐mediated dispersal. This study highlights the importance of including spatial structure and environmental conditions when explaining patterns of community composition to better discriminate between the ecological processes that underlie biogeographical patterns of communities composed of native and non‐native fish species.     

Predator dispersal determines the effect of connectivity on prey diversity

Linking local communities to a metacommunity can positively affect diversity by enabling immigration of dispersal-limited species and maintenance of sink populations. However, connectivity can also negatively affect diversity by allowing the spread of strong competitors or predators. In a microcosm experiment with five ciliate species as prey and a copepod as an efficient generalist predator, we analysed the effect of connectivity on prey species richness in metacommunities that were either unconnected, connected for the prey, or connected for both prey and predator. Presence and absence of predator dispersal was cross-classified with low and high connectivity. The effect of connectivity on local and regional richness strongly depended on whether corridors were open for the predator. Local richness was initially positively affected by connectivity through rescue of species from stochastic extinctions. With predator dispersal, however, this positive effect soon turned negative as the predator spread over the metacommunity. Regional richness was unaffected by connectivity when local communities were connected only for the prey, while predator dispersal resulted in a pronounced decrease of regional richness. The level of connectivity influenced the speed of richness decline, with regional species extinctions being delayed for one week in weakly connected metacommunities. While connectivity enabled rescue of prey species from stochastic extinctions, deterministic extinctions due to predation were not overcome through reimmigration from predator-free refuges. Prey reimmigrating into these sink habitats appeared to be directly converted into increased predator abundance. Connectivity thus had a positive effect on the predator, even when the predator was not dispersing itself. Our study illustrates that dispersal of a species with strong negative effects on other community members shapes the dispersal-diversity relationship. When connections enable the spread of a generalist predator, positive effects of connectivity on prey species richness are outweighed by regional extinctions through predation.     

Factors influencing species richness in lacustrine zooplankton

Frequent dispersal events are expected to elevate local species richness in island-like habitats such as lakes. However, the importance of dispersal can be hard to evaluate if other factors cause large background variability in species composition and richness. In this paper, we review empirical studies on ecological factors known or expected to influence species richness in zooplankton communities of inland lakes. We then present summaries of two recent case studies. Our objectives are twofold: we first look for effects of biotic interactions on species richness and species composition, and then evaluate whether the expected effects of dispersal are likely to be detected on a background of large variability caused by other ecological factors and interactions. Species richness within lakes appears to be primarily controlled by factors related to lake size, lake productivity, water quality, and fish predation levels. One case study indicated a slight, but significant, positive effect of lake density and lake area in the surrounding landscape on species richness, suggesting that frequent dispersal events may enhance species richness. This local variation in species richness is superimposed on regional variation in species pools.     

Predicting reef fish connectivity from biogeographic patterns and larval dispersal modelling to inform the development of marine reserve networks

Developing networks of no-take marine reserves is often hindered by uncertainty in the extent to which local marine populations are connected to one another through larval dispersal and recruitment (connectivity). While patterns of connectivity can be predicted by larval dispersal models and validated by empirical methods, biogeographic approaches have rarely been used to investigate connectivity at spatial scales relevant to reserve networks (10's–100's of km). Here, species assemblage patterns in coral reef fish were used together with an individual-based model of dispersal of reef fish larvae to infer patterns of connectivity in a ∼300 km wide region in the Philippines that included the Bohol Sea and adjacent bodies of water. A dominant current flows through the study region, which may facilitate connectivity among >100 no-take reserves. Connectivity was first investigated by analysing data on the presence/absence of 216 species of reef fish and habitat variables across 61 sites. Hierarchical clustering of sites reflecting species assemblage patterns distinguished a major group of sites in the Bohol Sea (Bray–Curtis similarity >70%) from sites situated in adjacent bodies of water (bays, channels between islands and a local sea). The grouping of sites could be partly explained by a combination of degree of embayment, % cover of sand and % cover of rubble (Spearman rank correlation, ρ_w = 0.42). The individual-based model simulated dispersal of reef fish larvae monthly for three consecutive years in the region. The results of simulations, using a range of pelagic larval durations (15–45 days), were consistent with the species assemblage patterns. Sites in the model that showed strongest potential connectivity corresponded to the majority of sites that comprised the Bohol Sea group suggested by hierarchical clustering. Most sites in the model that exhibited weak connectivity were groups of sites which had fish assemblages that were least similar to those in the Bohol Sea group. Concurrent findings from the two approaches suggest a strong influence of local oceanography and geography on broad spatial patterns of connectivity. The predictions can be used as an initial basis to organise existing reserves to form ecologically meaningful networks. This study showed that species assemblage patterns could be a viable supplementary indicator of connectivity if used together with predictions from a larval dispersal model and if the potential effect of habitat on the structuring of species assemblages is taken into consideration.     

Reduced Global Genetic Differentiation of Exploited Marine Fish Species

Knowledge on genetic structure is key to understand species connectivity patterns and to define the spatiotemporal scales over which conservation management plans should be designed and implemented. The distribution of genetic diversity (within and among populations) greatly influences species ability to cope and adapt to environmental changes, ultimately determining their long-term resilience to ecological disturbances. Yet, the drivers shaping connectivity and structure in marine fish populations remain elusive, as are the effects of fishing activities on genetic subdivision. To investigate these questions, we conducted a meta-analysis and compiled genetic differentiation data (F_ST/Φ_ST estimates) for more than 170 fish species from over 200 published studies globally distributed. We modeled the effects of multiple life-history traits, distance metrics, and methodological factors on observed population differentiation indices and specifically tested whether any signal arising from different exposure to fishing exploitation could be detected. Although the myriad of variables shaping genetic structure makes it challenging to isolate the influence of single drivers, results showed a significant correlation between commercial importance and genetic structure, with widespread lower population differentiation in commercially exploited species. Moreover, models indicate that variables commonly used as proxy for connectivity, such as larval pelagic duration, might be insufficient, and suggest that deep-sea species may disperse further. Overall, these results contribute to the growing body of knowledge on marine genetic connectivity and suggest a potential effect of commercial fisheries on the homogenization of genetic diversity, highlighting the need for additional research focused on dispersal ecology to ensure long-term sustainability of exploited marine species.     

Spatial extent of analysis influences observed patterns of population genetic structure in a widespread darter species (Percidae)

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A multi‐metric fish index to assess the environmental condition of estuaries

The development of a multi‐metric fish index, the Estuarine Fish Community Index (EFCI), for assessing estuarine environments is described. The index comprises 14 metrics or measures that represent four broad fish community attributes: species diversity and composition, species abundance, nursery function and trophic integrity. The individual metrics were evaluated using data that were collected on a South African estuary that was degraded and in which rehabilitation measures were implemented. The evaluation suggested that the selected metrics adequately measure the condition of separate but related components of estuarine fish communities and that these reflect environmental condition. Reference conditions and metric thresholds were derived from fish community data collected during an extensive national study. The final multi‐metric index was then constructed and evaluated. The EFCI combines both structural and functional attributes of estuarine fish communities and integrates these to provide both a robust and sensitive method for assessing the ecological condition of estuarine systems. It is also an effective communication tool for converting ecological information into an easily understood format for managers, policy makers and the general public.     

Evaluating functional diversity conservation for freshwater fishes resulting from terrestrial protected areas

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Homogenization of fish assemblages in different lake depth strata at local and regional scales

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The effect of lake morphology on aquatic vegetation development and changes under the influence of eutrophication

Data on aquatic and emergent vegetation, morphology and water quality from 274 Polish lowland lakes surveyed in the years 1996–2009 were used to validate the preliminary typology of Polish lakes based on macrophytes and to indicate the environmental parameters which most significantly determine the vegetation patterns in lakes under various morphological conditions. In highly alkaline lowland lakes representing non-disturbed conditions the key determinants influencing the vegetation patterns were mean depth and the shape of the littoral. Three morphological lake types were distinguished: shallow (<3.5 m), deep, and additionally, within the latter, deep ribbon-shaped, with a clearly elongated base and steep bed slopes. The lake types varied in their vegetation patterns developed under non-disturbed conditions. In the shallow lakes, the share of the phytolittoral in the total lake area (%phytol) was the highest (40–100%, 72.3% on average) and the maximum colonisation depth (C_max) the lowest (3.2 m as the maximum) compared to the lakes from both deep types. In the ribbon-shaped deep lakes, %phytol and the plant coverage (%cover) were the lowest, the proportion of submerged vegetation was extraordinarily high (over 90%) and the emergent vegetation was extremely sparsely developed (<6%) compared to the lakes of the two other types.The alterations of aquatic vegetation resulting from the eutrophication process in distinguished morphological lake types were explored. Within the macrophyte variables tested, three groups of indicators were distinguished: (a) metrics performing best in selected lake types, i.e. the type-specific indicators (abundance metrics, %Pota), (b) metrics performing equally well in all the lake types, considered as the universal indicators (e.g. S_Chara, %Subm and %Emerg) and (c) metrics performing poorly in all the lake types, with generally limited applicability (most of the metrics on syntaxonomic richness). In the shallow lakes, %cover and %phytol performed notably better than in deep lakes, whereas C_max worked best in deep lakes and showed the strongest response in the deep regular-shaped lakes. Moreover, in deep regular-shaped lakes the number of communities of stoneworts and submerged plants (S_Chara and S_Subm), and in deep ribbon-shaped lakes the proportion of area inhabited by vascular plant communities (%Pota) performed exceptionally better than in the other two lake types. The most universal metrics, performing equally well in all the lake types, were the proportions of submerged (%Subm) and emergent (%Emerg) vegetation in the total phytolittoral area.     

Interactive effects of diversity, nutrients and elevated CO2 on experimental plant communities

The effects of species richness and elevated CO₂ on community productivity under altered nutrient levels were studied in experimental herbaceous communities composed of species from the Midwestern United States annual community, which consists of three functional groups C₃, C₄ and N‐fixers. Aboveground and belowground biomass were measured at flowering stage and at the end of the experiment when fruits of most plants were ripe. At the low nutrient level, species richness did not have a significant effect on community productivity. However, at the high nutrient level, the community biomass decreased with decreasing species richness at both ambient and elevated CO₂ in the first harvest, and at elevated CO₂ in the second harvest. At low nutrient level, CO₂ slightly increased community biomass at medium and high species richness. At high nutrient level, CO₂ significantly increased community biomass in all species‐richness treatments in the first harvest, but a significant response was observed only in the high richness treatment in the second harvest. At the functional group level, biomass of C₃ responded positively to CO₂, and C₄ responded very negatively to CO₂. The N‐fixers responded positively to CO₂ at low and medium species richness, but negatively at high species richness, showing a CO₂×richness interaction. CO₂ increased species evenness in the communities, depending on nutrient level. Species varied in the responses of light‐saturated net photosynthesis (P_max) to elevated CO₂, even within functional groups. Our findings suggest that (1) the relationship between productivity and species diversity was dependent on nutrient levels. (2) Species diversity enhances responses of communities to elevated CO₂. (3) Harvest time can affect the results of diversity‐productivity experiments. (4) Responses of C₃, C₄, and N‐fixers to elevated CO₂ in communities did not follow the prediction based on functional groups or plants grown individually, rather it depended on species richness.