Extinction order and altered community structure rapidly disrupt ecosystem functioning

By causing extinctions and altering community structure, anthropogenic disturbances can disrupt processes that maintain ecosystem integrity. However, the relationship between community structure and ecosystem functioning in natural systems is poorly understood. Here we show that habitat loss appeared to disrupt ecosystem functioning by affecting extinction order, species richness and abundance. We studied pollination by bees in a mosaic of agricultural and natural habitats in California and dung burial by dung beetles on recently created islands in Venezuela. We found that large-bodied bee and beetle species tended to be both most extinction-prone and most functionally efficient, contributing to rapid functional loss. Simulations confirmed that extinction order led to greater disruption of function than predicted by random species loss. Total abundance declined with richness and also appeared to contribute to loss of function. We demonstrate conceptually and empirically how the non-random response of communities to disturbance can have unexpectedly large functional consequences.     

Effects of organism size and community composition on ecosystem functioning

We tested (1) if the size of dominant species influenced ecosystem functioning in food webs consisting of bacteria, algae, and protozoa; (2) whether those effects changed in importance through time; and (3) how those effects compared with differences in diversity among experimental food webs. We constructed food webs using two size fractions of organisms that differed in individual mass by approximately two orders of magnitude. We measured total biomass and respiration (total CO₂ production) as two aspects of ecosystem functioning. We also compared these size‐dependent patterns in functioning across two levels of species richness. Initially, organism size strongly influenced total community biomass. With time, however, biomass and respiration eventually converged in communities dominated by large or small species. We conclude that after sufficient time for community development any differences in ecosystem functioning resulted from differences in community composition, including species richness, but not the size of the dominant organisms.     

Intraspecific diversity loss in a predator species alters prey community structure and ecosystem functions

Loss in intraspecific diversity can alter ecosystem functions, but the underlying mechanisms are still elusive, and intraspecific biodiversity–ecosystem function (iBEF) relationships have been restrained to primary producers. Here, we manipulated genetic and functional richness of a fish consumer (Phoxinus phoxinus) to test whether iBEF relationships exist in consumer species and whether they are more likely sustained by genetic or functional richness. We found that both genotypic and functional richness affected ecosystem functioning, either independently or interactively. Loss in genotypic richness reduced benthic invertebrate diversity consistently across functional richness treatments, whereas it reduced zooplankton diversity only when functional richness was high. Finally, losses in genotypic and functional richness altered functions (decomposition) through trophic cascades. We concluded that iBEF relationships lead to substantial top-down effects on entire food chains. The loss of genotypic richness impacted ecological properties as much as the loss of functional richness, probably because it sustains “cryptic” functional diversity.

Global change is expected to generate a loss of intraspecific diversity worldwide. This mesocosm study explores whether loss of genetic and functional diversity in a predator species affects community and ecosystem functioning of lower trophic levels in pond ecosystems, revealing that diversity loss in a single consumer species can impact an entire ecosystem, reducing its functionality.     

An experimental test of the effect of plant functional group diversity on arthropod diversity

Characteristics used to categorize plant species into functional groups for their effects on ecosystem functioning may also be relevant to higher trophic levels. In addition, plant and consumer diversity should be positively related because more diverse plant communities offer a greater variety of resources for the consumers. Thus, the functional group composition and richness of a plant community may affect the composition and diversity of the herbivores and even higher trophic levels associated with that community. We tested this hypothesis by sampling arthropods with a vacuum sampler (34 531 individuals of 494 species) from an experiment in which we manipulated plant functional group richness and composition. Plant manipulations included all combinations of three functional groups (forbs, C₃ graminoids, and C₄ graminoids) removed zero, one, or two at a time from grassland plots at Cedar Creek Natural History Area, MN. Although total arthropod species richness was unrelated to plant functional group richness or composition, the species richness of some arthropod orders was affected by plant functional group composition. Two plant characteristics explained most of the effects of plant functional groups on arthropod species richness. Nutritional quality, a characteristic related to ecosystem functioning, and taxonomic diversity, a characteristic not used to designate plant functional groups, seemed to affect arthropod species richness both directly and indirectly. Thus, plant functional groups designated for their effects on ecosystem processes will only be partially relevant to consumer diversity and abundance.     

Biodiversity influences ecosystem functioning in aquatic angiosperm communities

Knowledge of the connection between aquatic plant diversity and ecosystem processes is still limited. To examine how plant species diversity affects primary productivity, plant nutrient use, functional diversity of secondary producers and population/community stability, we manipulated submerged angiosperm species diversity in a field experiment lasting 15 weeks. Plant richness increased the shoot density for three of four species. Polyculture biomass production was enhanced by increasing richness, with positive complementarity and selection effects causing positive biodiversity effects. Species richness enhanced the community stability for biomass production and shoot density. Sediment ammonium availability decreased with plant diversity, suggesting improved nutrient usage with increasing plant richness. Interestingly, positive multitrophic effects of plant species richness on structural and functional diversity of macrobenthic secondary producers were recorded. The results suggest that mixed seagrass meadows play an important role for ecosystem functioning and thus contribute to the provision of goods and services in coastal areas.     

Ecosystem Functions across Trophic Levels Are Linked to Functional and Phylogenetic Diversity

In experimental systems, it has been shown that biodiversity indices based on traits or phylogeny can outperform species richness as predictors of plant ecosystem function. However, it is unclear whether this pattern extends to the function of food webs in natural ecosystems. Here we tested whether zooplankton functional and phylogenetic diversity explains the functioning of 23 natural pond communities. We used two measures of ecosystem function: (1) zooplankton community biomass and (2) phytoplankton abundance (Chl a). We tested for diversity-ecosystem function relationships within and across trophic levels. We found a strong correlation between zooplankton diversity and ecosystem function, whereas local environmental conditions were less important. Further, the positive diversity-ecosystem function relationships were more pronounced for measures of functional and phylogenetic diversity than for species richness. Zooplankton and phytoplankton biomass were best predicted by different indices, suggesting that the two functions are dependent upon different aspects of diversity. Zooplankton community biomass was best predicted by zooplankton trait-based functional richness, while phytoplankton abundance was best predicted by zooplankton phylogenetic diversity. Our results suggest that the positive relationship between diversity and ecosystem function can extend across trophic levels in natural environments, and that greater insight into variation in ecosystem function can be gained by combining functional and phylogenetic diversity measures.     

植物功能群去除对高寒草甸群落结构、多样性及生产力的影响

群落中物种的丧失在干扰下普遍存在,但对生态系统过程和功能的影响仍存在较大不确定性。选取青藏高原东缘典型高寒草甸为对象,开展优势植物功能群的梯度去除试验,以模拟长期过牧干扰下物种的损失。经过连续两个生长季的功能群去除,我们对群落的物种组成、结构、多样性和生物量等特征进行了分析,探讨了上述指标的响应过程和机制。研究结果表明：（1）功能群的去除降低了群落高度,增加了物种均匀度,并显著影响了禾草、杂草优势比以及功能群多样性和优势度;（2）同时,去除操作显著减小了凋落物量与禾草生物量,并显著影响了群落地上生物量;（3）进一步分析还发现,禾草、莎草和杂草功能群之间存在显著的竞争关系,群落生产力主要取决于禾草功能群并随物种均匀度的增大而显著减小。上述结果表明,禾草在高寒草甸群落中占据竞争优势地位,植物功能群的损失主要通过改变种间竞争关系、引起有机物质丢失影响群落过程和功能。     

Nesting strategies affect altitudinal distribution and habitat use in Alpine dung beetle communities

1. Dung beetles are key contributors to a suite of ecosystem services. Understanding the factors that dictate their distributions is a necessary step towards preventing negative impacts of biodiversity loss. 2. Alpine dung beetle communities were analysed along altitudinal gradients to assess how different components of the community, defined in terms of nesting strategy [dung‐ovipositing Aphodiidae (DOAs), soil‐ovipositing Aphodiidae (SOAs) and two paracoprid (PAR) groups, Geotrupidae and Scarabaeidae] and parameters relevant to dung removal rates (species richness, total biomass and functional diversity), are distributed, and to identify to which environmental factors they respond. 3. Species richness declined with altitude. There was no significant variation in functional diversity or total biomass in relation to altitude. There were significant variations when considered by nesting group: DOA species richness and biomass decreased, SOA biomass increased, and Geotrupidae biomass showed a non‐linear trend, as altitude increased. 4. Functional diversity and total species richness were positively related to vegetation cover. DOA species richness was highest in forest and scrub; SOA species richness was highest in grassland and PAR species richness was lowest in rocky areas. 5. Dung beetle species show different trends in species richness and biomass depending on nesting strategy. Management to promote the dung beetle community should include maintenance of a mosaic of habitat types. Given the likely importance of species richness and biomass to ecosystem functioning, and the complimentary effect of different dung beetle groups, such a strategy may protect and enhance the ecosystem services that Alpine dung beetles provide.     

Recovery of mammal diversity in tropical forests: a functional approach to measuring restoration

Ecological restoration is increasingly applied in tropical forests to mitigate biodiversity loss and recover ecosystem functions. In restoration ecology, functional richness, rather than species richness, often determines community assembly, and measures of functional diversity provide a mechanistic link between diversity and ecological functioning of restored habitat. Vertebrate animals are important for ecosystem functioning. Here, we examine the functional diversity of small‐to‐medium sized mammals to evaluate the diversity and functional recovery of tropical rainforest. We assess how mammal species diversity and composition and functional diversity and composition, vary along a restoration chronosequence from degraded pasture to “old‐growth” tropical rainforest in the Wet Tropics of Australia. Species richness, diversity, evenness, and abundance did not vary, but total mammal biomass and mean species body mass increased with restoration age. Species composition in restoration forests converged on the composition of old‐growth rainforest and diverged from pasture with increasing restoration age. Functional metrics provided a clearer pattern of recovery than traditional species metrics, with most functional metrics significantly increasing with restoration age when taxonomic‐based metrics did not. Functional evenness and dispersion increased significantly with restoration age, suggesting that niche complementarity enhances species' abundances in restored sites. The change in community composition represented a functional shift from invasive, herbivorous, terrestrial habitat generalists and open environment specialists in pasture and young restoration sites, to predominantly endemic, folivorous, arboreal, and fossorial forest species in older restoration sites. This shift has positive implications for conservation and demonstrates the potential of tropical forest restoration to recover rainforest‐like, diverse faunal communities.     

Short-term responses of an alpine meadow community to removal of a dominant species along a fertilization gradient

Aims The relationship between biodiversity and ecosystem functioning has intrigued ecologists for several decades, but the effect of loss of a dominant species on community structure and functioning along a nutrient gradient remains poorly understood. The aim of this paper was to test the effect of a dominant species on community structure and function by conducting a species removal experiment along a fertilization gradient.Methods We removed the population of a dominant species (Elymus nutans) in a long-term fertilization field in an alpine meadow on the Tibetan Plateau, China. Univariate general linear models were used to evaluate the effects of fertilization and removal on above-ground vegetation characteristics, including photosynthetically active radiation in the understory, species richness, Shannon–Weiner diversity index, Simpson's dominance index, above-ground biomass (including different functional groups) and seedling richness and density.Important findings Results revealed that after two plant growing seasons, there was no significant effect of the removal of a dominant species on species richness and diversity of the remaining vegetation, but the biomass of forbs and seedling recruitment were significantly increased indicative of the potential for long-term effects. Moreover, removal had a large effect at high fertilization levels, but little effect when fertilization levels were low. Our studies indicated that community response to loss of a dominant species was mainly dependent on resource availability and the remaining functional group identities. We also found seedling recruitment was usually more sensitive to the influence of competition of dominant species than the established vegetation in the short term.     

Trophic complementarity drives the biodiversity–ecosystem functioning relationship in food webs

The biodiversity–ecosystem functioning (BEF) relationship is central in community ecology. Its drivers in competitive systems (sampling effect and functional complementarity) are intuitive and elegant, but we lack an integrative understanding of these drivers in complex ecosystems. Because networks encompass two key components of the BEF relationship (species richness and biomass flow), they provide a key to identify these drivers, assuming that we have a meaningful measure of functional complementarity. In a network, diversity can be defined by species richness, the number of trophic levels, but perhaps more importantly, the diversity of interactions. In this paper, we define the concept of trophic complementarity (TC), which emerges through exploitative and apparent competition processes, and study its contribution to ecosystem functioning. Using a model of trophic community dynamics, we show that TC predicts various measures of ecosystem functioning, and generate a range of testable predictions. We find that, in addition to the number of species, the structure of their interactions needs to be accounted for to predict ecosystem productivity.     

Effect of (a)synchronous light fluctuation on diversity,functional and structural stability of a marine phytoplankton metacommunity

Disentangling the mechanisms that maintain the stability of communities and ecosystem properties has become a major research focus in ecology in the face of anthropogenic environmental change. Dispersal plays a pivotal role in maintaining diversity in spatially subdivided communities, but only a few experiments have simultaneously investigated how dispersal and environmental fluctuation affect community dynamics and ecosystem stability. We performed an experimental study using marine phytoplankton species as model organisms to test these mechanisms in a metacommunity context. We established three levels of dispersal and exposed the phytoplankton to fluctuating light levels, where fluctuations were either spatially asynchronous or synchronous across patches of the metacommunity. Dispersal had no effect on diversity and ecosystem function (biomass), while light fluctuations affected both evenness and community biomass. The temporal variability of community biomass was reduced by fluctuating light and temporal beta diversity was influenced interactively by dispersal and fluctuation, whereas spatial variability in community biomass and beta diversity were barely affected by treatments. Along the establishing gradient of species richness and dominance, community biomass increased but temporal variability of biomass decreased, thus highest stability was associated with species-rich but highly uneven communities and less influenced by compensatory dynamics. In conclusion, both specific traits (dominance) and diversity (richness) affected the stability of metacommunities under fluctuating conditions.     

Functional diversity is positively associated with biomass for lake diatoms

1. Recent work has emphasised the benefit of using functional measures when relating biodiversity to ecosystem functioning. In this study, we investigated the extent to which functional and taxonomic diversity might be related to summed biovolume in community assemblages of 212 species of diatoms collected from 65 temperate lakes in western and central Quebec, Canada. 2. We quantified functional diversity as both the total path‐length of a functional dendrogram (FD) and the variance in species traits (TV) for a given community. Selected traits included both size and responses to a set of environmental variables known to be influential for diatom communities. 3. Species richness, as well as both FD and TV, was positively associated with total diatom biovolume at the level of the entire diatom community, suggesting that diversity in response types (particularly to total phosphorus and pH) is important for diatom community production. 4. Although functional measures of diversity did not provide enhanced explanatory power over species richness, we argue that an exploration of functional traits potentially allows greater insight into the mechanisms underlying biodiversity–ecosystem functioning relations, indicating which traits might be most influential in driving community biomass production.     

Woody plant phylogenetic diversity mediates bottom–up control of arthropod biomass in species-rich forests

Global change is predicted to cause non-random species loss in plant communities, with consequences for ecosystem functioning. However, beyond the simple effects of plant species richness, little is known about how plant diversity and its loss influence higher trophic levels, which are crucial to the functioning of many species-rich ecosystems. We analyzed to what extent woody plant phylogenetic diversity and species richness contribute to explaining the biomass and abundance of herbivorous and predatory arthropods in a species-rich forest in subtropical China. The biomass and abundance of leaf-chewing herbivores, and the biomass dispersion of herbivores within plots, increased with woody plant phylogenetic diversity. Woody plant species richness had much weaker effects on arthropods, but interacted with plant phylogenetic diversity to negatively affect the ratio of predator to herbivore biomass. Overall, our results point to a strong bottom–up control of functionally important herbivores mediated particularly by plant phylogenetic diversity, but do not support the general expectation that top–down predator effects increase with plant diversity. The observed effects appear to be driven primarily by increasing resource diversity rather than diversity-dependent primary productivity, as the latter did not affect arthropods. The strong effects of plant phylogenetic diversity and the overall weaker effects of plant species richness show that the diversity-dependence of ecosystem processes and interactions across trophic levels can depend fundamentally on non-random species associations. This has important implications for the regulation of ecosystem functions via trophic interaction pathways and for the way species loss may impact these pathways in species-rich forests.     

Biodiversity acts as insurance of productivity of bacterial communities under abiotic perturbations

Anthropogenic disturbances are detrimental to the functioning and stability of natural ecosystems. Critical ecosystem processes driven by microbial communities are subjected to these disturbances. Here, we examine the stabilizing role of bacterial diversity on community biomass in the presence of abiotic perturbations such as addition of heavy metals, NaCl and warming. Bacterial communities with a diversity gradient of 1–12 species were subjected to the different treatments, and community biomass (OD₆₀₀) was measured after 24 h. We found that initial species richness and phylogenetic structure impact the biomass of communities. Under abiotic perturbations, the presence of tolerant species in community largely contributed in community biomass production. Bacterial diversity stabilized the biomass across the treatments, and differential response of bacterial species to different perturbations was the key reason behind these effects. The results suggest that biodiversity is crucial for maintaining the stability of ecosystem functioning and acts as ecological insurance under abiotic perturbations. Biodiversity in natural ecosystems may also uphold the ecosystem functioning under anthropogenic disturbance.     

Dominance by an obligate annual affects the morphological characteristics and biomass production of a planted wetland macrophyte community

Aims Biodiversity–ecosystem function experiments can test for causal relationships between planting diversity and community productivity. Planting diversity is routinely introduced as a design element in created wetlands, yet substantive support for the finding that early diversity positively affects ecosystem functioning is lacking for wetlands. We conducted a 2-year diversity–productivity experiment using freshwater wetland mesocosms to investigate community biomass production as affected by planted macrophyte functional richness.Methods A richness gradient of macrophytes in four emergent wetland plant functional groups was established in freshwater mesocosms for two consecutive years. Species-specific aboveground morphological traits of plant size were measured at peak growth in both years; rooting depth was measured for each species in the second year. Aboveground biomass (AGB) and belowground biomass (BGB) were harvested after peak growth in the second year; first year AGB was estimated from morphological traits in constructed regression equations. Net richness effects (i.e. both complementarity effects and selection effects) were calculated using an additive partitioning method.Important findings Species richness had a positive effect on community AGB relative to monocultures in the first year. In the second year, mean AGB was significantly reduced by competition in the most species-rich mixtures and all mixtures underyielded relative to the average monoculture. Competition for soil resources was weaker belowground, whereby root distribution at depths>20cm was reduced at the highest richness levels but overall BGB production was not affected. Changes in species biomass were strongly reflected by variation in species morphological traits, and species above and belowground performances were highly correlated. The obligate annual (Eleocharis obtusa), a dominant competitor, significantly contributed to the depression of perennial species' growth in the second growing season. To foster primary productivity with macrophyte richness in early successional communities of created wetlands where ruderal strategies are favored and competition may be stronger than species complementarity, unsystematic planting designs such as clustering the same or similar species could provide protection for some individuals. Additionally, engineering design elements fostering spatial or temporal environmental variability (e.g. microtopography) in newly created wetlands helps diversify the responses of wetland macrophyte species to their environment and could allow for greater complementarity in biomass production.     

Realistic Variation in Species Composition Affects Grassland Production,Resource Use and Invasion Resistance

We investigated the effects of realistic variation in plant species and functional group composition, with species occurring at realistic abundances, on ecosystem processes in exotic-dominated California grassland communities. Progressive species removals from microcosm communities, designed to mimic nested variation in diversity observed in the field, reduced grassland production, resistance to intentional invasions, and resistance to natural colonization by new species. Three lines of evidence point to the particular importance of intensified competition within a single functional group—late-active forbs—in explaining the observed effects of realistic species loss order on community resistance. First, reduced success of naturally colonizing species in more diverse assemblages was dominated by declining colonization by late-active forbs. Second, increasing late-active forb biomass appeared to reduce the biomass of intentionally introduced yellow starthistle (Centaurea solstitialis, a late-season forb) both within and across diversity levels. Finally, starthistle addition reduced biomass of resident late-season forbs but not of any other functional group. Increasing diversity increased light levels and soil moisture availability in spring and summer, providing a proximate mechanism linking our realistic species loss order to decreased community resistance. Starthistle addition reduced light and soil moisture availability but not N across richness levels, mirroring the apparent effects of the additional late-active forb species present in higher diversity treatments. Species losses that entail the early loss of whole or key functional groups could, through mechanisms like those we explore, have greater ecosystem consequences than those suggested by randomized-loss experiments.     

Predicting productivity in tropical reservoirs: The roles of phytoplankton taxonomic and functional diversity

Primary productivity is intimately linked with biodiversity and ecosystem functioning. Much of what is known today about such relationship has been based on the manipulation of species richness. Other facets of biodiversity, such as functional diversity, have been neglected within this framework, particularly in freshwater systems. We assess the adequacy of different diversity measures, from species richness and evenness, to functional groups richness and functional diversity indices, to predict primary productivity in 19 tropical reservoirs of central Brazil, built to generate hydroelectric energy. We applied linear mixed models (and model selection based on the Akaike’s information criterion) to achieve our goal, using chlorophyll-a concentration as a surrogate for primary productivity. A total of 412 species were collected in this study. Overall we found a positive relation between productivity and diversity, with functional evenness representing the only exception. The most parsimonious models never included functional group classifications, with at least one continuous measure of functional diversity being present in many models. The best model included only species richness and explained 24.1% of variability in productivity. We therefore advise the use of species richness as an indicator of productivity in tropical freshwater environments. However, since the productivity–diversity relationship is known to be scale dependent, we recommend the use of continuous measures of functional diversity in future biodiversity and ecosystem functioning studies, in order to be certain that all functional differences between communities are being accounted for.     

Does functional redundancy of communities provide insurance against human disturbances? An analysis using regional-scale stream invertebrate data

Human-induced reductions in species richness might alter the quality of ecosystem services when the remaining species are not able to substitute the functions provided by extirpated species. We examined how human disturbances (nutrient enrichment, land use intensification, instream habitat degradation and the presence of alien species) influence the species richness of stream invertebrates. Stream invertebrates (425 native species) were collected by kick and sweep sampling technique at 274 stream sites covering the entire area of Hungary. We measured the species richness, functional richness (i.e. number of unique functional roles provided by community members) and functional redundancy (i.e. the functional insurance of the community) using information on the feeding habits of each species. To remove the effect of natural variability, we tested the effect of stressors on the residuals of models relating species richness, functional richness and functional redundancy with natural environmental gradients. Our results showed that species richness was negatively influenced by instream habitat degradation and nutrient enrichment. Independent of the way of quantifying functional richness and functional redundancy, we found that functional richness is more sensitive to human impact than functional redundancy of stream invertebrates. The finding that a reduction of species richness is associated with a loss of unique functional roles (functional richness) is important for conservation issues, because the number of unique functional roles is usually regarded as driver of ecosystem functioning.     

Hydrological extremes modulate nutrient dynamics in mediterranean climate streams across different spatial scales

We studied benthic macroinvertebrate communities upstream and downstream of five small reservoirs (surface release in autumn–winters) (north Spain) to assess the effect of flow regulation on structural and functional characteristics of stream ecosystems. We based our approach on the use of structural metrics (density, biomass, richness and diversity) in combination with two functional diversity indices based on biological and ecological traits: FD_PG index, related to species richness, and FD_Q, which incorporates evenness across taxa. Although water physicochemical parameters were unaffected by the reservoirs during the study period (autumn–winter), macroinvertebrate metrics were lower below the dams, with detritivores (shredders and collector-gatherers) being the most affected. The alder leaf breakdown rate estimated by the litter-bag technique was related to the density, biomass, richness, diversity and FD_PG index of shredders, compromising the ecosystem functioning. The most plausible origin for the observed differences in macroinvertebrate metrics between upstream and downstream reaches was the change of the flow regime caused by the impoundments at downstream sites, leading to droughts in summer in those naturally permanently flowing streams. The observed functional diversity loss might reduce the chances of the community to override natural or man-induced fluctuations in their environment with possible repercussions on important ecosystem functions and services.