Effects Of Species Loss Research Articles

Structural but not functional resistance of frugivore-plant interaction networks to the defaunation process

Defaunation is the process of sequential loss of larger animal species caused by anthropogenic activities such as deforestation and hunting. This phenomenon has potential to disrupt the ecosystem stability, as well as their functional performance through the disruption of trophic interactions. We evaluated the effect of defaunation on structure and function in frugivore-plant interaction networks. We characterized interaction networks in two areas in northern Colombia and used a simulation model of species extinction in three different scenarios. The first scenario eliminated species based on body size, measured by body mass, according to the progressive effect of non-random species loss (defaunation); the second scenario eliminated species according to their contribution to network structure (CNS); and finally, the third scenario eliminated species according to their seed dispersal potential (SDP). Based on these simulations we evaluated the effect of species loss on the structural patterns (nestedness and modularity) and the functional diversity of the frugivore community, through the indexes of functional richness (FRic) and functional evenness (FEve). The loss of species with larger body sizes increased nestedness and did not affect modularity, whereas in the CNS scenario both patterns were affected. The FRic index decreased in the first stages of extinction by defaunation and by SDP, while the FEve index did not suffer significant variations in any scenario. The combination of interaction network analysis with functional diversity indices allows direct quantification of the robustness of network structural patterns and the vulnerability of the functional capacity of frugivore communities in the face of defaunation.

Mechanisms underlying interaction frequencies and robustness in a novel seed dispersal network: lessons for restoration.

As human-caused extinctions and invasions accumulate across the planet, understanding the processes governing ecological functions mediated by species interactions, and anticipating the effect of species loss on such functions become increasingly urgent. In seed dispersal networks, the mechanisms that influence interaction frequencies may also influence the capacity of a species to switch to alternative partners (rewiring), influencing network robustness. Studying seed dispersal interactions in novel ecosystems on O'ahu island, Hawai'i, we test whether the same mechanisms defining interaction frequencies can regulate rewiring and increase network robustness to simulated species extinctions. We found that spatial and temporal overlaps were the primary mechanisms underlying interaction frequencies, and the loss of the more connected species affected networks to a greater extent. Further, rewiring increased network robustness, and morphological matching and spatial and temporal overlaps between partners were more influential on network robustness than species abundances. We argue that to achieve self-sustaining ecosystems, restoration initiatives can consider optimal morphological matching and spatial and temporal overlaps between consumers and resources to maximize chances of native plant dispersal. Specifically, restoration initiatives may benefit from replacing invasive species with native species possessing characteristics that promote frequent interactions and increase the probability of rewiring (such as long fruiting periods, small seeds and broad distributions).

Climate, immigration and speciation shape terrestrial and aquatic biodiversity in the European Alps

Quaternary climate fluctuations can affect speciation in regional biodiversity assembly in two non-mutually exclusive ways: a glacial species pump, where isolation in glacial refugia accelerates allopatric speciation, and adaptive radiation in underused adaptive zones during ice-free periods. We detected biogeographic and genetic signatures associated with both mechanisms in the assembly of the biota of the European Alps. Age distributions of endemic and widespread species within aquatic and terrestrial taxa (amphipods, fishes, amphibians, butterflies and flowering plants) revealed that endemic fish evolved only in lakes, are highly sympatric, and mainly of Holocene age, consistent with adaptive radiation. Endemic amphipods are ancient, suggesting preglacial radiation with limited range expansion and local Pleistocene survival, perhaps facilitated by a groundwater-dwelling lifestyle. Terrestrial endemics are mostly of Pleistocene age and are thus more consistent with the glacial species pump. The lack of evidence for Holocene adaptive radiation in the terrestrial biome is consistent with faster recolonization through range expansion of these taxa after glacial retreats. More stable and less seasonal ecological conditions in lakes during the Holocene may also have contributed to Holocene speciation in lakes. The high proportion of young, endemic species makes the Alpine biota vulnerable to climate change, but the mechanisms and consequences of species loss will likely differ between biomes because of their distinct evolutionary histories.

Island and Mountain Ecosystems as Testbeds for Biological Control in the Anthropocene

For centuries, islands and mountains have incited the interest of naturalists, evolutionary biologists and ecologists. Islands have been the cradle for biogeography and speciation theories, while mountain ranges have informed how population adaptation to thermal floors shapes the distribution of species globally. Islands of varying size and mountains’ altitudinal ranges constitute unique “natural laboratories” where one can investigate the effects of species loss or global warming on ecosystem service delivery. Although invertebrate pollination or seed dispersal processes are steadily being examined, biological control research is lagging. While observations of a wider niche breadth among insect pollinators in small (i.e., species-poor) islands or at high (i.e., colder) altitudes likely also hold for biological control agents, such remains to be examined. In this Perspective piece, we draw on published datasets to show that island size alone does not explain biological control outcomes. Instead, one needs to account for species’ functional traits, habitat heterogeneity, host community make-up, phenology, site history or even anthropogenic forces. Meanwhile, data from mountain ranges show how parasitism rates of Noctuid moths and Tephritid fruit flies exhibit species- and context-dependent shifts with altitude. Nevertheless, future empirical work in mountain settings could clarify the thermal niche space of individual natural enemy taxa and overall thermal resilience of biological control. We further discuss how global databases can be screened, while ecological theories can be tested, and simulation models defined based upon observational or manipulative assays in either system. Doing so can yield unprecedented insights into the fate of biological control in the Anthropocene and inform ways to reinforce this vital ecosystem service under global environmental change scenarios.

Resources do not limit compensatory response of a tallgrass prairie plant community to the loss of a dominant species

AbstractThe effect of species loss on ecosystem productivity is determined by both the functional contribution of the species lost, and the response of the remaining species in the community. According to the mass ratio hypothesis, the loss of a dominant plant species, which has a larger proportionate contribution to productivity, is expected to exert an overwhelming effect on this important ecosystem function. However, via competitive release, loss of a dominant species can provide the opportunity for other plant species to establish, thrive and become abundant in the community, potentially compensating for the function lost. Furthermore, if resource limitation is removed, then the compensatory response of function to the loss of a dominant species should be greater and more rapid than if resources are more limiting.To evaluate how resources may limit compensation of above‐ground productivity to the loss of a dominant plant species, we experimentally removed the C4perennial tallgrass,Andropogon gerardii, from intact plant communities. We added water for 4 years, as well as nitrogen in the fourth year, to test the effect of resource limitation on the compensatory response.Overall, above‐ground biomass production increased in the remaining community with both water and nitrogen addition. However, this increase in biomass production was not sufficient to fully compensate for the loss ofA. gerardii, indicating water and nitrogen were not limiting short‐term compensation in this community.Following the removal of the dominant species, there was reordering of species abundances in the community, rather than changes in species richness. The C4grassBouteloua curtipendulawas the most responsive species, increasing by 57.9% in abundance with water addition and 91.0% with both water and nitrogen addition. Despite this dramatic increase in abundance, its short stature and lower per capita biomass production prevented this species from compensating for the loss ofA. gerardii.Synthesis. Short‐term compensation after the loss of a dominant plant species can be hastened by increased resource availability, but ultimately full compensation appears to be limited by the presence and abundance of species in the remaining community that possess traits that allow them compensate for the species lost.

Trait-based filtering mediates the effects of realistic biodiversity losses on ecosystem functioning

Biodiversity losses are a major driver of global changes in ecosystem functioning. While most studies of the relationship between biodiversity and ecosystem functioning have examined randomized species losses, trait-based filtering associated with species-specific vulnerability to drivers of diversity loss can strongly influence how ecosystem functioning responds to declining biodiversity. Moreover, the responses of ecosystem functioning to diversity loss may be mediated by environmental variability interacting with the suite of traits remaining in depauperate communities. We do not yet understand how communities resulting from realistic diversity losses (filtered by response traits) influence ecosystem functioning (via effect traits of the remaining community), especially under variable environmental conditions. Here, we directly test how realistic and randomized plant diversity losses influence productivity and invasion resistance across multiple years in a California grassland. Compared with communities based on randomized diversity losses, communities resulting from realistic (drought-driven) species losses had higher invasion resistance under climatic conditions that matched the trait-based filtering they experienced. However, productivity declined more with realistic than with randomized species losses across all years, regardless of climatic conditions. Functional response traits aligned with effect traits for productivity but not for invasion resistance. Our findings illustrate that the effects of biodiversity losses depend not only on the identities of lost species but also on how the traits of remaining species interact with varying environmental conditions. Understanding the consequences of biodiversity change requires studies that evaluate trait-mediated effects of species losses and incorporate the increasingly variable climatic conditions that future communities are expected to experience.

Multitrophic diversity sustains ecological complexity by dampening top-down control of a shallow marine benthic food web.

Biodiversity is typically considered as a one-dimensional metric (e.g., species richness), yet the consequences of species loss may be different depending on where extinctions occur in the food web. Here, I used a manipulative field experiment in a temperate subtidal marine system to explore the implications of diversity loss at multiple trophic levels for ecosystem functioning and food web structure. The four manipulated predators included the small painted goby and common prawn, which are also fed on by the larger black goby and shore crab. Antagonistic interactions between the manipulated predators (e.g., intraguild predation, intimidation, interference competition) limited their negative effects on the rest of the food web. Top-down control was so suppressed at the highest level of multitrophic diversity that the resulting food webs were as complex and productive as those containing no manipulated predators. Negative interactions between the predators weakened as multitrophic diversity decreased, however, resulting in stronger consumption of lower trophic levels and a simpler food web with lower rates of two key ecosystem processes: primary production and decomposition. These results show how indirect interactions between predators on multiple trophic levels help to promote the complexity and functioning of natural systems.

Evolution of realized Eltonian niches across Rajidae species

AbstractThe notion that closely related species resemble each other in ecological niche space (i.e., phylogenetic dependence) has been a long‐standing, contentious paradigm in evolutionary biology, the incidence of which is important for predicting the ecosystem‐level effects of species loss. Despite being examined across a multitude of terrestrial taxa, many aspects of niche conservatism have yet to be explored in marine species, especially for characteristics related to resource use and trophic behavior (Eltonian niche characteristics, ENCs). We combined ENCs derived from stable isotope ratios at assemblage‐ and species‐levels with phylogenetic comparative methods, to test the hypotheses that benthic marine fishes (1) exhibit similar assemblage‐wide ENCs regardless of geographic location and (2) display phylogenetically dependent ENCs at the species level. We used a 12‐species sub‐set of the monophyletic group Rajidae sampled from three independent assemblages (Central California, Gulf of Alaska, and Northwest Atlantic), which span two ocean basins. Assemblage‐level ENCs implied low trophic diversity and high evenness, suggesting that Rajidae assemblages may exhibit a well‐defined trophic role, a trend consistent regardless of geographic location. At the species level, we found evidence for phylogenetic dependence of ENCs relating to trophic diversity (i.e., isotopic niche width; SEAc). Whether individuals can be considered functional equivalents across assemblages is hard to ascertain because we did not detect a significant phylogenetic signal for ENCs relating to trophic function (e.g., trophic position). Thus, additional, complimentary approaches are required to further examine the phylogenetic dependence of species functionality. Our approach illustrates the potential of stable isotope‐derived niche characteristics to provide insight on macroecological processes occurring across evolutionary time, which could help predict how assemblages may respond to the effects of species loss.

Biodiversity Loss Threatens the Current Functional Similarity of Beta Diversity in Benthic Diatom Communities

The global biodiversity loss has increased the need to understand the effects of decreasing diversity, but our knowledge on how species loss will affect the functioning of communities and ecosystems is still very limited. Here, the levels of taxonomic and functional beta diversity and the effect of species loss on functional beta diversity were investigated in an estuary that provides a naturally steep environmental gradient. The study was conducted using diatoms that are among the most important microorganisms in all aquatic ecosystems and globally account for 40% of marine primary production. Along the estuary, the taxonomic beta diversity of diatom communities was high (Bray-Curtis taxonomic similarity 0.044) and strongly controlled by the environment, particularly wind exposure, salinity, and temperature. In contrast, the functional beta diversity was low (Bray-Curtis functional similarity 0.658) and much less controlled by the environment. Thus, the diatom communities stayed functionally almost similar despite large changes in species composition and environment. This may indicate that, through high taxonomic diversity and redundancy in functions, microorganisms provide an insurance effect against environmental change. However, when studying the effect of decreasing species richness on functional similarity of communities, simulated species loss to 45% of the current species richness decreased functional similarity significantly. This suggests that decreasing species richness may increase variability and reduce the stability and resilience of communities. These results highlight the importance of high taxonomic biodiversity for the stable functioning of benthic communities.

Ecosystem Functioning of Great Salt Lake Wetlands

Like many wetlands worldwide, Great Salt Lake (GSL) wetlands have been declining. Yet, little is known about the ecosystem functions provided by the different GSL wetland plant species. This knowledge gap hinders predictions of the effects of species loss and restoration practices on ecosystem functioning. To better understand how the loss of different habitat types affects the provisioning of ecosystem functions, we quantified eight functions and multifunctionality (the support of multiple functions simultaneously) across seven dominant GSL wetland habitat types. Habitats varied greatly in their capacity to perform functions. However, no single habitat type supported all eight functions even at 20% of the maximum value for each individual function. We found that native plants Typha latifolia and Schoenoplectus acutus and invasive Phragmites australis had the highest levels of multifunctionality. Although these three species were able to support more functions, we found that a diversity of habitats are required to maintain the breadth of ecosystem functions examined. This study supports the idea that habitat heterogeneity is critical in supporting a multifunctional environment, and that habitat homogenization may cause a reduction in functioning provided by GSL wetlands.

Species loss drives ecosystem function in experiments, but in nature the importance of species loss depends on dominance

AbstractAimDecades of experimental research have conclusively shown a positive relationship between species richness and ecosystem function. However, authoritative reviews find no consensus on how species loss affects function in natural communities. We analyse experimental and observational data in an identical way and test whether they produce similar results.LocationNorth America and Europe (experimental communities); global (natural communities).Time periodExperimental communities: 1998–2013; natural communities: 1982–2018.Major taxa studiedExperimental communities: temperate grassland plants; natural communities: temperate grassland plants, tropical forest trees, kelp forest producers and native bees.MethodsWe used an approach inspired by the Price equation to analyse 129 datasets from experimental and natural communities worldwide. We tested how the effects of species loss on ecosystem function varied with dominance and the non‐randomness of species loss and, in turn, how these two factors differed between experiments and observations.ResultsStudies carried out in experimental and natural communities reached different conclusions regarding the effects of species loss. First, species loss had greater effects on ecosystem function in experiments than in nature. Second, the importance of species loss was negatively correlated with dominance in nature because as dominance increased, lost species were increasingly those contributing little to ecosystem function. Although experimental and natural communities exhibited similar levels of dominance, an analogous relationship was not possible in experiments because the order of species loss was randomized by design.Main conclusionsSpecies loss was sometimes, but not always, the major driver of loss of function in nature. Variation in the importance of species loss was not messy and context dependent; instead, it was predicted by functional dominance. Although results from experimental and natural communities were similar in several key ways, they differed in that species loss was a consistent predictor of ecosystem function in experiments and not in nature.

Biotic factors determine ecosystem processes in environments with different hydrological regimes

Abstract The interest in understanding ecosystem functioning has grown in recent years due to the effects of species loss on ecosystem processes. Even though biotic and abiotic factors control ecosystem processes, their relative influence may vary according to ecosystem dynamics. In flood and coastal plains, these dynamics are mainly represented by flood pulses and hydroregime, respectively. The objective of this study was to investigate the importance of abiotic and biotic factors for the ecosystem processes represented by zooplankton secondary production (SP), biomass (ZB), and resource use efficiency (RUE) in lentic waterbodies subjected to different hydrological regimes. We hypothesised that abiotic factors would more strongly determine the ecosystem processes in temporary waterbodies and floodplain lakes, given their greater susceptibility to environmental changes. Biotic factors would be more relevant in coastal lagoons due to their greater temporal stability. Sampling was undertaken quarterly over 1 year in eight coastal lagoons, 10 temporary ponds and five floodplain lakes. The environments were characterised in relation to limnological variables, and zooplankton functional divergence, functional dispersion (FDis), functional evenness, functional richness, and taxonomic richness were measured. Analysis of variance (ANOVA) was used to verify seasonal changes in SP, ZB, RUE, functional diversity, richness, and abiotic factors. Linear mixed models were used to determine which abiotic and biotic factors were the most important for ZB, SP, and RUE. In the coastal lagoons, RUE differed over time. In the temporary ponds and floodplain lakes, no seasonal significant differences were observed for any of the zooplankton production variables. The linear mixed model analyses showed that models composed mainly of biotic factors were better fitted to the production variables. For coastal lagoons, phytoplankton density affected ZB, SP, and RUE increasing them by 9.9 mg DW/m3, 12.4 mg DW/m3, and 1.23, respectively. For temporary ponds, FDis lowered ZB by 6.9 mg DW/m3 and taxonomic richness increased SP and RUE by 14.2 mg DW/m3 and 1.17, respectively. For floodplain lakes, FDis lowered ZB it by 9.9 mg DW/m3 and functional divergence lowered RUE by 0.81. The present study demonstrates that biotic factors are the main determinants of ecosystem processes in neotropical lentic waterbodies, irrespective of their annual hydrological regimes. Complementarity effects and high functional diversity are more important in more stable environments, whereas redundancy and low functional diversity prevail in environments subject to more frequent environmental changes. Biotic factors play a major role in ensuring the functioning of aquatic ecosystems and indicate the important role of biodiversity in enabling ecosystem states to be maintained after disturbances and to prevent changes in ecosystem processes.

Defaunation Leads to Functional Loss in a Tropical Biodiversity Hotspot

Defaunation is considered one of the main drivers of modifications in tropical ecosystems, extirpating many large-sized vertebrates, which in turn compromises key ecological functions. Although much attention has been given to predict the effects of species loss on ecological processes, there is a lack of information on the large-scale effects of defaunation. Knowledge gaps such as at which spatial scales biodiversity loss affects ecosystem functioning and ecological functions, and what is the relationship between species loss and preservation of ecological functions, remain poorly understood. Mammals perform important ecological functions, but are widely affected by habitat loss and modification, being considered as priority for conservation worldwide. Thus, determining the impact of land use changes on ecological patterns and process performed or influenced by mammals is of critical importance. Here, we detected erosion in the prevalence of ecological functions performed by mammals mediated by changes in the landscape structure of a tropical biodiversity hotspot in Brazil. By analyzing the loss of different ecological functions (vertebrate and invertebrate predation, seed dispersal, seed depredation, herbivory) in a defaunation gradient, we observed that vulnerable functions (performed by sensitive species) were positively related to patch size and forest cover and negatively related to anthropogenic cover. These relationships were reversed for persistent functions (performed by resilient species). Vulnerable functions were virtually restricted to large forest remnants, while persistent functions were prevalent in human-modified landscapes. Our study adds knowledge on how large-scale defaunation mediated by changes in landscape structure affects ecological functions.

Generalists are more specialized in low-resource habitats, increasing stability of ecological network structure

Linking mechanistic processes to the stability of ecological networks is a key frontier in ecology. In trophic networks, "modules"-groups of species that interact more with each other than with other members of the community-confer stability, mitigating effects of species loss or perturbation. Modularity, in turn, is shaped by the interplay between species' diet breadth traits and environmental influences, which together dictate interaction structure. Despite the importance of network modularity, variation in this emergent property is poorly understood in complex natural systems. Using two years of field data, we quantified interactions between a rich community of lepidopteran herbivores and their host plants across a mosaic of low-resource serpentine and high-resource nonserpentine soils. We used literature and our own observations to categorize herbivore species as generalists (feeding on more than one plant family) or specialists (feeding on one plant family). In both years, the plant-herbivore network was more modular on serpentine than on nonserpentine soils-despite large differences in herbivore assemblage size across years. This structural outcome was primarily driven by reduction in the breadth of host plant use by generalist species, rather than by changes in the composition of species with different fundamental diet breadths. Greater modularity-and thus greater stability-reflects environmental conditions and plastic responses by generalist herbivores to low host plant quality. By considering the dual roles of species traits and ecological processes, we provide a deeper mechanistic understanding of network modularity, and suggest a role for resource availability in shaping network persistence.

Including rewiring in the estimation of the robustness of mutualistic networks

Abstract Species are entangled within communities by their interactions in such a manner that their local extinction may unchain coextinction cascades and impact community dynamics and stability. Despite increasing attention, simulation models to estimate the robustness of interaction networks largely neglect the important role of interaction rewiring, that is, the ability of species to switch partners. Here we propose a new method to incorporate the potential of species to replace lost partners into a widely used coextinction model to estimate network robustness. In this model, species are allowed to rewire their interactions after initial loss of partners according to probabilities derived from well‐known mechanisms that determine mutualistic interactions, for example, trait matching, phenological overlap and abundances. To illustrate the use of this method, we analyzed a well‐sampled dataset of mutualistic plant–hummingbird interactions. We found that (a) in general, rewiring increases the estimated robustness, (b) networks are similarly robust to the loss of pollinators or plants, (c) morphological matching and phenological overlap leads to higher robustness, (d) when multiple rewiring mechanisms are combined, however, robustness increases little, and (e) rewiring tends to increase robustness more in scenarios when the loss of generalist species occurs first. Our results suggest that the same mechanisms known to drive plant–hummingbird network structure are relevant in buffering the effects of species loss via rewiring. The method proposed here can be applied to a wide range of interaction networks and is flexible to the inclusion of other variables important in determining interactions for specific systems. It also allows changes on the assumptions regarding the importance of distinct mechanisms, for instance including a hierarchical relationship, which facilitates insights into the relative importance of multiple variables influencing network disassembling. The analytical framework we offer here represents a step towards a more realistic estimation on how species loss may affect the integrity of interaction networks.

Experimental loss of generalist plants reveals alterations in plant-pollinator interactions and a constrained flexibility of foraging

Species extinctions undermine ecosystem functioning, with the loss of a small subset of functionally important species having a disproportionate impact. However, little is known about the effects of species loss on plant-pollinator interactions. We addressed this issue in a field experiment by removing the plant species with the highest visitation frequency, then measuring the impact of plant removal on flower visitation, pollinator effectiveness and insect foraging in several sites. Our results show that total visitation decreased exponentially after removing 1–4 most visited plants, suggesting that these plants could benefit co-occurring ones by maintaining high flower visitor abundances. Although we found large variation among plant species, the redistribution of the pollinator guild affected mostly the other plants with high visitor richness. Also, the plant traits mediated the effect of removal on flower visitation; while visitation of plants which had smaller inflorescences and more sugar per flower increased after removal, flower visitors did not switch between flower shapes and visitation decreased mostly in plants visited by many morpho-species of flower visitors. Together, these results suggest that the potential adaptive foraging was constrained by flower traits. Moreover, pollinator effectiveness fluctuated but was not directly linked to changes of flower visitation. In conclusion, it seems that the loss of generalist plants alters plant-pollinator interactions by decreasing pollinator abundance with implications for pollination and insect foraging. Therefore, generalist plants have high conservation value because they sustain the complex pattern of plant-pollinator interactions.

Diversidad funcional en el ensamblaje de la ictiofauna del Océano Pacífico Oriental Tropical: Una revisión de dos décadas en su enfoque

Background. One of the most relevant topics in ecology and evolution is understanding the relationship between biological and functional diversity at the ecosystem level; both important in the evolutionary processes and the structuring of complex communities. Goals. In this essay, the explanatory hypotheses focused on global patterns of the distribution of species are described along with selected hypotheses relating species richness/biodiversity to ecosystem function, and the differentiation of the terms guild and functional group are discussed. Methods. Both biodiversity and functional diversity are key in the evolutionary processes and the structuring of complex communities and thus examples of functional equivalence of convergent evolution derivatives are presented in terms of the form and ecological habits of fishes of the Tropical Eastern Pacific Ocean. Finally, the importance of redundancy in ecosystem functioning is examined as well as the impact of environmental disturbances on ecosystem function. Results. In general, systems with low species richness and redundancy within functional groups are more vulnerable to disturbances. However, despite the extensive effort to understand the relationship between species richness/biodiversity and ecosystem functioning, there is no consensus on the effect of species loss on the functioning of the ecosystem. Some hypothesize that each species is unique and plays a unique role in the ecosystem whereas alternate hypotheses indicate that species overlap in function supporting sustainability at the ecosystem level, such that the removal of one species function may be replaced by another. Conclusions.The most widely accepted concept is that a greater number of species increases the efficiency in the use of resources and also provides resilience against environmental changes or impacts through functional redundancy.

Body size mediates the relationship between spider (Arachnida: Araneae) assemblage composition and prey consumption rate: results of a mesocosm experiment in the Yukon, Canada.

Many ecological assemblages are undergoing rapid changes in composition and diversity, and changes at one trophic level can have direct and cascading effects on other trophic levels. Prey consumption typically increases with predator diversity due to niche complementarity and sampling effects. However, the effect of functional traits and interactions between predator species mean that the relationship is far from simple. In July 2016, we performed a series of experiments in the Yukon, Canada, to investigate the relationship between spider assemblage composition and prey consumption, with a focus on the wolf spider Pardosa lapponica (Thorell 1872). We carried out feeding trials, in which P. lapponica and other spider species were offered potential prey, as well as mesocosm experiments, in which we varied spider assemblage composition within small enclosures. We confirmed that P. lapponica is a generalist consumer, individual consumption rate increased with spider body size, and that intraguild predation is present. We found that prey consumption was greatest in the least diverse assemblage but consumption did increase with predator functional trait variation and biomass. The best model of prey consumption included predator assemblage composition, variation in body mass, biomass, and all interactions. The body size of a spider affects its trophic niche, energy requirements, and its interactions with other spiders. As a result, body size mediates the relationship between spider assemblage composition and prey consumption. A deeper understanding of the relationships between traits and functions will allow us to better predict the effect of species loss or gain on ecosystem functions.

Loss of Generalist Plant Species and Functional Diversity Decreases the Robustness of a Seed Dispersal Network

SummaryUnderstanding cascading effects of species loss is a major challenge for ecologists. Traditionally, the robustness of ecological networks has been evaluated based on simulation studies where primary extinctions occur at random or as a function of species specialization, ignoring other important biological factors. Here, we estimate the robustness of a seed dispersal network from a grassland–forest mosaic in southern Brazil, simulating distinct scenarios of woody plant species extinction, including scenarios where species are eliminated based on their evolutionary and functional distinctiveness. Our results suggest that the network is more robust when species are eliminated based on their evolutionary uniqueness, followed by random extinctions, the extinction of the most specialist species, functional distinctiveness and, at last, when the most generalist species are sequentially eliminated. Our results provide important information for grassland–forest mosaic management, as they indicate that loss of generalist species and functional diversity makes the system more likely to collapse.

Long-term effects of species loss on community properties across contrasting ecosystems.

Biodiversity loss can heavily affect the functioning of ecosystems, and improving our understanding of how ecosystems respond to biodiversity decline is one of the main challenges in ecology1-4. Several important aspects of the longer-term effects of biodiversity loss on ecosystems remain unresolved, including how these effects depend on environmental context5-7. Here we analyse data from an across-ecosystem biodiversity manipulation experiment that, to our knowledge, represents the world's longest-running experiment of this type. This experiment has been set up on 30 lake islands in Sweden that vary considerably in productivity and soil fertility owing to differences in fire history8,9. We tested the effects of environmental context on how plant species loss affected two fundamental community attributes-plant community biomass and temporal variability-over 20 years. In contrast to findings from artificially assembled communities10-12, we found that the effects of species loss on community biomass decreased over time; this decrease was strongest on the least productive and least fertile islands. Species loss generally also increased temporal variability, and these effects were greatest on the most productive and most fertile islands. Our findings highlight that the ecosystem-level consequences of biodiversity loss are not constant across ecosystems and that understanding and forecasting these consequences necessitates taking into account the overarching role of environmental context.