Biodiversity and Ecosystem Function

Testing effects of consumer richness, evenness and body size on ecosystem functioning

by Dan Perkins

1. Numerous studies have revealed (usually positive) relationships between biodiversity and ecosystem
functioning... more 1. Numerous studies have revealed (usually positive) relationships between biodiversity and ecosystem
functioning (B-EF), but the underpinning drivers are rarely addressed explicitly, hindering
the development of a more predictive understanding.
2. We developed a suite of statistical models (where we combined existing models with novel ones)
to test for richness and evenness effects on detrital processing in freshwater microcosms. Instead of
using consumer species as biodiversity units, we used two size classes within three species (six
types). This allowed us to test for diversity effects and also to focus on the role of body size and biomass.
3. Our statistical models tested for (i) whether performance in polyculture was more than the sum
of its parts (non-additive effects), (ii) the effects of specific type combinations (assemblage identity
effects) and (iii) whether types behaved differently when their absolute or relative abundances were
altered (e.g. because type abundance in polyculture was lower compared with monoculture). The
latter point meant we did not need additional density treatments.
4. Process rates were independent of richness and evenness and all types performed in an additive
fashion. The performance of a type was mainly driven by the consumers’ metabolic requirements
(connected to body size). On an assemblage level, biomass explained a large proportion of detrital
processing rates.
5. We conclude that B-EF studies would benefit from widening their statistical approaches. Further,
they need to consider biomass of species assemblages and whether biomass is comprised of
small or large individuals, because even if all species are present in the same biomass, small species
(or individuals) will performbetter.

Climate change and freshwater ecosystems: impacts across multiple levels of organization

by Dan Perkins

Fresh waters are particularly vulnerable to climate change because (i) these fragmented habitats contain many species... more Fresh waters are particularly vulnerable to climate change because (i) these fragmented habitats contain many species with limited abilities to disperse as their environment changes, (ii) water temperature and availability are climate-dependent, and (iii) many systems are already exposed to a plethora of anthropogenic stressors that could amplify the effects of climate change. Most studies of potential climate change effects in aquatic systems have focused on individuals or species populations, rather than the higher levels of organisation (i.e. communities, food webs, ecosystems). We propose that an understanding of the connections between these different levels, which are all ultimately based on individuals, can be used to develop a more coherent theoretical framework, via an integration of metabolic scaling, foraging theory, and ecological stoichiometry, to predict the ecological consequences of climate change. For instance, individual basal metabolic rate scales with body size, which is also a strong driver of food web structure and dynamics, and temperature, which determines many ecosystem process rates and key aspects of foraging behaviour. In addition increasing atmospheric CO2 is predicted to alter molar the CNP ratios of detrital inputs, which could lead to profound shifts in the stoichiometry of elemental fluxes between consumers and resources at the base of the food web. The different components of climate change (temperature, hydrology and atmospheric composition) not only affect multiple levels of biological organisation, but they also interact with the numerous other stressors that fresh waters are exposed to, and future research needs to address these potentially important synergies.

Environmental Warming and Biodiversity–Ecosystem Functioning in Freshwater Microcosms

by Dan Perkins

Predicting the effects of global warming on biodiversity–ecosystem functioning
(B–EF) relationships is... more Predicting the effects of global warming on biodiversity–ecosystem functioning
(B–EF) relationships is complicated by potential interactions among abiotic
and biotic variables at multiple levels of organisation, including adaptation
within regional species populations and changes in community composition
and species richness. We investigated the capacity for assemblages of
three freshwater invertebrate consumer species (Asellus aquaticus, Nemoura
cinerea and Sericostoma personatum) from temperate (southern England)
and boreal (northern Sweden) regions to respond to expected shifts in temperature
and basal resources, and quantified rates of a key ecosystem process (leaflitter
decomposition). Predictions of assemblage metabolism, derived from
allometric-body size and temperature scaling relationships, accounted for
approximately 40%of the variance in decomposition rates. Assemblage species
composition accounted for further variance, but species richness per se had no
discernible effect. Regional differences were evident in rates of leaf decomposition
across temperature and resourcemanipulations, and in terms of the processing
efficiency of temperate and boreal consumers of the same species (i.e. after
correcting for body size and metabolic capacity), suggesting that intraspecific
variation among local populations could modulate B–EF effects. These differences
have implications for extrapolating how environmental warming and
other aspects of climate change (e.g. species range shifts) might affect important
drivers of ecosystem functioning over large biogeographical scales.

Consistent temperature dependence of respiration across ecosystems contrasting in thermal history

by Dan Perkins

Ecosystem respiration is a primary component of the carbon cycle and understanding the mechanisms that determine its... more Ecosystem respiration is a primary component of the carbon cycle and understanding the mechanisms that determine its temperature dependence will be important for predicting how rates of carbon efflux might respond to global warming. We used a rare model system, comprising a network of geothermally heated streams ranging in temperature from 5 °C to 25 °C, to explore the nature of the relationship between respiration and temperature. Using this ‘natural experiment’, we tested whether the natal thermal regime of stream communities influenced the temperature dependence of respiration in the absence of other potentially confounding variables. An empirical survey of 13 streams across the thermal gradient revealed that the temperature dependence of whole-stream respiration was equivalent to the average activation energy of the respiratory complex (0.6–0.7 eV). This observation was also consistent for in-situ benthic respiration. Laboratory experiments, incubating biofilms from four streams across the thermal gradient at a range of temperatures, revealed that the activation energy and Q10 of respiration were remarkably consistent across streams, despite marked differences in their thermal history and significant turnover in species composition. Furthermore, absolute rates of respiration at standardised temperature were also unrelated to ambient stream temperature, but strongly reflected differences in biofilm biomass. Together, our results suggest that the core biochemistry,which drives the kinetics of oxidative respiratory metabolism, may be well conserved among diverse taxa and environments, and that the intrinsic sensitivity of respiration to temperature is not influenced by ambient environmental temperature.

Consistent temperature dependence of respiration across ecosystems contrasting in thermal history

by Gabriel Yvon-Durocher

Ecosystem respiration is a primary component of the carbon cycle and understanding the mechanisms that determine its... more Ecosystem respiration is a primary component of the carbon cycle and understanding the mechanisms that determine its temperature dependence will be important for predicting how rates of carbon efflux might respond to global warming. We used a rare model system, comprising a network of geothermally heated streams ranging in temperature from 5 °C to 25 °C, to explore the nature of the relationship between respiration and temperature. Using this ‘natural experiment’, we tested whether the natal thermal regime of stream communities influenced the temperature dependence of respiration in the absence of other potentially confounding variables. An empirical survey of 13 streams across the thermal gradient revealed that the temperature dependence of whole-stream respiration was equivalent to the average activation energy of the respiratory complex (0.6–0.7 eV). This observation was also consistent for in-situ benthic respiration. Laboratory experiments, incubating biofilms from four streams across the thermal gradient at a range of temperatures, revealed that the activation energy and Q10 of respiration were remarkably consistent across streams, despite marked differences in their thermal history and significant turnover in species composition. Furthermore, absolute rates of respiration at standardised temperature were also unrelated to ambient stream temperature, but strongly reflected differences in biofilm biomass. Together, our results suggest that the core biochemistry,which drives the kinetics of oxidative respiratory metabolism, may be well conserved among diverse taxa and environments, and that the intrinsic sensitivity of respiration to temperature is not influenced by ambient environmental temperature.

THE SMALL MAMMALS OF BARIO, KELABIT HIGHLANDS SARAWAK

by M.T. Abdullah, PhD

This paper discusses on the bat diversity in the highland of Sarawak. Some taxonomic errors. This paper discusses on the bat diversity in the highland of Sarawak. Some taxonomic errors.

Warming alters community size structure and ecosystem functioning

by Jonathan Grey

Proc Roy Soc London B 2012

Global warming can affect all levels of biological complexity, though we currently understand least about its... more Global warming can affect all levels of biological complexity, though we currently understand least about its potential impact on communities and ecosystems. At the ecosystem level, warming has the capacity to alter the structure of communities and the rates of key ecosystem processes they mediate. Here we assessed the effects of a 4°C rise in temperature on the size structure and taxonomic composition of benthic communities in aquatic mesocosms, and the rates of detrital decomposition they mediated. Warming had no effect on biodiversity, but altered community size structure in two ways. In spring, warmer systems exhibited steeper size spectra driven by declines in total community biomass and the proportion of large organisms. By contrast, in autumn, warmer systems had shallower size spectra driven by elevated total community biomass and a greater proportion of large organisms. Community-level shifts were mirrored by changes in decomposition rates. Temperature-corrected microbial and macrofaunal decomposition rates reflected the shifts in community structure and were strongly correlated with biomass across mesocosms. Our study demonstrates that the 4°C rise in temperature expected by the end of the century has the potential to alter the structure and functioning of aquatic ecosystems profoundly, as well as the intimate linkages between these levels of ecological organization.

Effects of urbanization on the dynamics of organic sediments in temperate lakes

by Tessa Francis

Bacterial Diversity Stabilizes Community Productivity

by Alexandre Jousset

Background

Stability is a crucial ecosystem feature gaining particular importance in face of increasing... more Background

Stability is a crucial ecosystem feature gaining particular importance in face of increasing anthropogenic stressors. Biodiversity is considered to be a driving biotic force maintaining stability, and in this study we investigate how different indices of biodiversity affect the stability of communities in varied abiotic (composition of available resources) and biotic (invasion) contexts.

Methodology/Principal Findings

We set up microbial microcosms to study the effects of genotypic diversity on the reliability of community productivity, defined as the inverse of the coefficient of variation of across-treatment productivity, in different environmental contexts. We established a bacterial diversity gradient ranging from 1 to 8 Pseudomonas fluorescens genotypes and grew the communities in different resource environments or in the presence of model invasive species. Biodiversity significantly stabilized community productivity across treatments in both experiments. Path analyses revealed that different aspects of diversity determined stability: genotypic richness stabilized community productivity across resource environments, whereas functional diversity determined stability when subjected to invasion.

Conclusions/Significance

Biodiversity increases the stability of microbial communities against both biotic and abiotic environmental perturbations. Depending on stressor type, varying aspects of biodiversity contribute to the stability of ecosystem functions. The results suggest that both genetic and functional diversity need to be preserved to ensure buffering of communities against abiotic and biotic stresses.

ESPASSA Project Team

by Neeraj Khera

Impacts of climate warming on lake fish assemblages: evidence from 24 European long-term data series.

by pietro volta

Jeppesen E., T. Mehner, I.J. Winfield, K. Kangur, J. Sarvala, D.Gerdeaux, M. Rask, H.J. Malmquist, K. Holmgren, P. Volta, S. Romo, R. Eckmann, A. Sandström, S. Blanco, A. Kangur, H. Ragnarsson Stabo, M. Meerhoff, A. Ventelä, M. Søndergaard, T.L. Lauridsen. Hydrobiologia. Major revision.

Fish play a key role in the trophic dynamics of lakes. With climate warming, complex changes in fish assemblage... more Fish play a key role in the trophic dynamics of lakes. With climate warming, complex changes in fish assemblage structure may be expected owing to direct effects on temperature and indirect effects operating through eutrophication, water level changes, stratification and salinisation. We reviewed published and new long-term fish data series from 24 European lakes. We found profound changes in fish assemblage composition, size and age structure during recent decades and a shift towards higher dominance of eurythermal species. The shift has occurred despite an overall reduction in nutrient loading that should have benefited the fish species typically inhabiting coldwater low-nutrient lakes and larger-sized individuals. The cold-stenothermic Arctic charr has been particularly affected and its abundance has decreased in the majority of the lakes where its presence was recorded. The harvest of cool-stenothermal trout has decreased substantially in two southern lakes. Vendace, whitefish and smelt show a different response depending on lake depth and latitude. Perch was apparently
stimulated in the north, with stronger year classes in warm years, but its abundance has declined in the southern Lake Maggiore. Where introduced, roach now seems to take advantage of the higher temperature after years of low populations. Eurythermal species such as common bream, pike-perch and shad are on the increase. The response of fish to the warming in recent decades has been surprisingly strong,
making them ideal sentinels for detecting and documenting climate-induced modifications of freshwater ecosystems.

Effects of introduction of common bream (Abramis brama) to a shallow Italian lake: dominance of small sizes-classes and deterioration in ecological state.

by pietro volta

Volta P., Jeppesen E., Leoni B., Campi B., Sala P., Garibaldi L., Lauridsen T., Winfield IJ. Biological invasions. Major revision.

Introduced non-native species are increasingly recognized as one of the main threats to biodiversity and ecosystem... more Introduced non-native species are increasingly recognized as one of the main threats to biodiversity and ecosystem functioning. We describe the population biology and life-history of the non-native fish common bream, Abramis brama (Pisces: Cyprinidae), which became successfully established in the late 1990s in Lake of Montorfano, a shallow lake in northern Italy which subsequently showed major changes in ecological state. Bream became the most abundant species and showed a remarkably short life cycle, with asymptotic length 33.5 cm, estimated mean length at first maturity 19.6 cm and total mortality rate 0.64 y-1. The diet of the bream was overwhelmingly dominated by microcrustaceans. Following bream establishment, zooplankton biomass decreased and phytoplankton biomass and the proportion of cyanobacteria increased markedly, indicating increased top-down control of zooplankton by fish. In addition, water transparency and coverage of submerged macrophytes declined and small native cyprinids disappeared. Selective removal of bream and perhaps stocking of native piscivorous could improve the ecological status of the lake.

Increasing antagonistic interactions cause bacterial communities to collapse at high diversity

by Alexandre Jousset

Biodiversity is a major determinant of ecosystem functioning. Species-rich communities often use resourcesmore Biodiversity is a major determinant of ecosystem functioning. Species-rich communities often use resources
more  efficiently  thereby  improving  community  performance.  However,  high  competition  within  diverse
communities may also reduce community functioning. We manipulated the genotypic diversity of Pseudomonas
fluorescens communities, a plant mutualistic species inhibiting pathogens. We measured antagonistic interactions
in vitro, and related these interactions to bacterial community productivity (root colonisation) and ecosystem
service (host plant protection). Antagonistic interactions increased disproportionally with species richness.
Mutual poisoning between competitors lead to a negative complementarity effect, causing a decrease in
bacterial density by up to 98% in diverse communities and a complete loss of plant protection. The results
emphasize  that  antagonistic  interactions  may  determine  community  functioning  and  cause  negative
biodiversity–ecosystem functioning relationships. Interference competition may thus be an additional key for
predicting the dynamics and performance of natural assemblages and needs to be implemented in future
biodiversity models.

Population-Level Metrics of Trophic Structure Based on Stable Isotopes and Their Application to Invasion Ecology

by Jonathan Grey

PLoS One 2012

Biological invasions are a significant driver of human-induced global change and many ecosystems sustain sympatric... more Biological invasions are a significant driver of human-induced global change and many ecosystems sustain sympatric invaders. Interactions occurring among these invaders have important implications for ecosystem structure and functioning, yet they are poorly understood. Here we apply newly developed metrics derived from stable isotope data to provide quantitative measures of trophic diversity within populations or species. We then use these to test the hypothesis that sympatric invaders belonging to the same functional feeding group occupy a smaller isotopic niche than their allopatric counterparts. Two introduced, globally important, benthic omnivores, Louisiana swamp crayfish (Procambarus clarkii) and carp (Cyprinus carpio), are sympatric in Lake Naivasha, Kenya. We applied our metrics to an 8-year data set encompassing the establishment of carp in the lake. We found a strong asymmetric interaction between the two invasive populations, as indicated by inverse correlations between carp abundance and measures of crayfish trophic diversity. Lack of isotopic niche overlap between carp and crayfish in the majority of years indicated a predominantly indirect interaction. We suggest that carp-induced habitat alteration reduced the diversity of crayfish prey, resulting in a reduction in the dietary niche of crayfish. Stable isotopes provide an integrated signal of diet over space and time, offering an appropriate scale for the study of population niches, but few isotope studies have retained the often insightful information revealed by variability among individuals in isotope values. Our population metrics incorporate such variation, are robust to the vagaries of sample size and are a useful additional tool to reveal subtle dietary interactions among species. Although we have demonstrated their applicability specifically using a detailed temporal dataset of species invasion in a lake, they have a wide array of potential ecological applications.

Population-level metrics of trophic structure based on stable isotopes and their application to invasion ecology

by Ian Donohue

Jackson, M.C., Donohue, I., Jackson, A.L., Britton, J.R., Harper, D.M. & Grey, J. (2012) Population-level metrics... more Jackson, M.C., Donohue, I., Jackson, A.L., Britton, J.R., Harper, D.M. & Grey, J. (2012) Population-level metrics of trophic structure based on stable isotopes and their application to invasion ecology. PLOS One 7: e31757.

Biological invasions are a significant driver of human-induced global change and many ecosystems sustain sympatric invaders. Interactions occurring among these invaders have important implications for ecosystem structure and functioning, yet they are poorly understood. Here we apply newly developed metrics derived from stable isotope data to provide quantitative measures of trophic diversity within populations or species. We then use these to test the hypothesis that sympatric invaders belonging to the same functional feeding group occupy a smaller isotopic niche than their allopatric counterparts. Two introduced, globally important, benthic omnivores, Louisiana swamp crayfish (Procambarus clarkii) and carp (Cyprinus carpio), are sympatric in Lake Naivasha, Kenya. We applied our metrics to an 8-year data set encompassing the establishment of carp in the lake. We found a strong asymmetric interaction between the two invasive populations, as indicated by inverse correlations between carp abundance and measures of crayfish trophic diversity. Lack of isotopic niche overlap between carp and crayfish in the majority of years indicated a predominantly indirect interaction. We suggest that carp-induced habitat alteration reduced the diversity of crayfish prey, resulting in a reduction in the dietary niche of crayfish. Stable isotopes provide an integrated signal of diet over space and time, offering an appropriate scale for the study of population niches, but few isotope studies have retained the often insightful information revealed by variability among individuals in isotope values. Our population metrics incorporate such variation, are robust to the vagaries of sample size and are a useful additional tool to reveal subtle dietary interactions among species. Although we have demonstrated their applicability specifically using a detailed temporal dataset of species invasion in a lake, they have a wide array of potential ecological applications.

Temporal variability within disturbance events regulates their effects on natural communities

by Ian Donohue

García Molinos, J. & Donohue, I. (2011) Temporal variability within disturbance events regulates their effects on... more García Molinos, J. & Donohue, I. (2011) Temporal variability within disturbance events regulates their effects on natural communities. Oecologia 166: 795-806.

Disturbances are inherently variable in time and space. Such heterogeneity comprises a key determinant of ecosystem responses to disturbance. Temporal patterns can, however, vary significantly both among and within individual disturbance events. While recent research has demonstrated an importance of the former, studies on the effects of variability within perturbations have consistently confounded temporal variability with other disturbance attributes (e.g. overall intensity or duration). We established a field experiment to test explicitly the hypothesis that the temporal pattern within perturbations can drive ecosystem responses independently of other disturbance traits. We examined the effects of two disturbance regimes comprising sediment pulses of contrasting temporal pattern (constant and temporally variable intensities) on the benthic invertebrate assemblage of a headwater stream. The overall intensity, duration, timing and frequency of the perturbations were, however, identical. Invertebrates drifting during the temporally variable pulses were more abundant and differed in taxonomic and trophic structure than those exposed to constant perturbations. Moreover, whereas temporal patterns of disturbance events had no immediate effect on benthic invertebrate assemblages in situ, assemblages exposed to the constant perturbations took longer to recover from sediment disturbances than those exposed to temporally variable perturbations. Our results demonstrate that variability in the temporal pattern of intensity within individual perturbations can regulate, independently of other disturbance attributes, the extent and type of ecosystem responses to, and recovery from, disturbances. Effective environmental management and policy therefore necessitate the explicit quantification of temporal patterns of intensity both within and among perturbations.

Importance of consumers on exposed and sheltered rocky shores

by Ian Donohue

O'Connor, N.E., Donohue, I., Crowe, T.P. & Emmerson, M.C. (2011) Importance of consumers on exposed and sheltered... more O'Connor, N.E., Donohue, I., Crowe, T.P. & Emmerson, M.C. (2011) Importance of consumers on exposed and sheltered rocky shores. Marine Ecology Progress Series 443: 65-75

It is often suggested that the relative importance of biotic processes, such as recruit- ment, competition and predation of marine benthic species, varies predictably along a gradient of exposure to wave action. Several established models of community dynamics on rocky shores pre- dict that top-down processes are more important for structuring communities on sheltered than on exposed shores. To test the relative dominance of top-down processes, we first measured the establishment of key benthic species (mussels, barnacles and algae) on 3 sheltered and 3 exposed rocky shores in southwest Ireland over two 6 mo periods. We then manipulated the presence of consumers (e.g. grazing gastropods, crabs, whelks), using caged exclosures, on 2 sheltered and 2 exposed shores to test for an interaction between effects of consumers and shore exposure on the establishment of benthic species. In contrast to predictions, we found that consumers strongly affected establishment of all species regardless of shore exposure. We also found that shore expo- sure was not a reliable predictor for spatial and temporal variation in rates of establishment of sessile benthic species. Our findings provide experimental evidence which demonstrates the importance of consumers in early post-settlement stages of benthic species—essential for the development of benthic−pelagic models.

Persistent predator–prey dynamics revealed by mass extinction

by Lauren Sallan

End-Devonian extinction and a bottleneck in the early evolution of modern jawed vertebrates

by Lauren Sallan

Heads or tails: staged diversification in vertebrate evolutionary radiations

by Lauren Sallan