André T. C. Dias

Handbook of protocols for standardized measurement of terrestrial invertebrate functional traits

Summary 1. Trait-based approaches are increasingly being used to test mechanisms underlying species assemblages and biotic interactions across a wide range of organisms including terrestrial arthropods and to investigate consequences for ecosystem processes. Such an approach relies on the standardized measurement of functional traits that can be applied across taxa and regions. Currently, however, unified methods of trait measurements are lacking for terrestrial arthropods and related macroinvertebrates (terrestrial invertebrates hereafter). 2. Here, we present a comprehensive review and detailed protocol for a set of 29 traits known to be sensitive to global stressors and to affect ecosystem processes and services. We give rec- ommendations how to measure these traits under standardized conditions across various ter- restrial invertebrate taxonomic groups. 3. We provide considerations and approaches that apply to almost all traits described, such as the selection of species and individuals needed for the measurements, the importance of intraspecific trait variability, how many populations or communities to sample and over which spatial scales. 4. The approaches outlined here provide a means to improve the reliability and predictive power of functional traits to explain community assembly, species diversity patterns and ecosystem processes and services within and across taxa and trophic levels, allowing compar- ison of studies and running meta-analyses across regions and ecosystems. 5. This handbook is a crucial first step towards standardizing trait methodology across the most studied terrestrial invertebrate groups, and the protocols are aimed to balance general applicability and requirements for special cases or particular taxa. Therefore, we envision this handbook as a common platform to which researchers can further provide methodological input for additional special cases.

An experimental framework to identify community functional components driving ecosystem processes and services delivery

There is a growing consensus that the distribution of species trait values in a community can greatly determine ecosystem processes and services delivery. Two distinct components of community trait composition are hypothesized to chiefly affect ecosystem processes: (i) the average trait value of the species, quantified by community-weighted mean trait values (CWM; related to the mass ratio hypothesis) and (ii) the degree to which trait values differ between species in a community, quantified by different indices of functional diversity (FD; related to non-additive community effects). The uncertainty on the relative effect of these two components is stimulating an increasing number of empirical studies testing their effects on ecosystem processes and services delivery. We suggest, however, that the interdependence between CWM and FD poses a challenge on disentangling their relative importance. We present a framework that allows designing experiments to decouple and assess the effects of these two community functional components on ecosystem processes and services. To illustrate the framework, we focused on leaf litter decomposition, as this is an essential process related to important ecosystem services. Using simulations, we applied the framework for plant leaf litter traits (litter nitrogen and phenolic content) that are related to litter decomposition. CWM and FD generally showed a hump-shaped relationship (i.e. at more extreme CWM values, communities can have only low FD values). Within this relationship, we showed that it is possible to select quasi-orthogonal combinations of CWM and FD that can be treated statistically. Within these orthogonal CWM and FD combinations, it is also possible to select species assemblages controlling for other community parameters, such as total biomass, total density and species richness. Synthesis. The framework provides a novel approach for designing experiments to decouple the effects of CWM and FD of communities on ecosystem processes, which otherwise cannot be easily disentangled. To apply the framework and design proper experimental layouts, it is essential to have a priori knowledge of the key traits by which species affect ecosystem processes and service delivery.

Population dynamics of the marsupial Micoureus demerarae in small fragments of Atlantic Coastal Forest in Brazil

Patterns of population fluctuation, reproductive activity and age structure were studied in populations of the marsupial Micoureus demerarae occupy- ing two small (7.0 and 8.8 ha) fragments of Atlantic Coastal Forest in southeastern Brazil, from 1995 to 1998. Males, but not females, were observed to move between populations. Estimated sizes of the populations in each fragment were very small, usually below 20 individuals. Breeding usually occurred from September to April. Population peaks came mostly by the end of this season, the delay reflecting the time required for the young to become trappable. In August 1997, the area was hit by a fire severely affecting the smaller fragment. Populations were synchronous before the fire, although they became asynchronous after it, possibly in the short term only. Small population sizes, synchrony and presumable male-biased migra- tion are all likely to make the set of populations more vulnerable to extinction than expected for a metapopulation.

Plant Species Composition Can Be Used as a Proxy to Predict Methane Emissions in Peatland Ecosystems After Land-Use Changes

Land-use change in peatlands affects important drivers of CH4 emission such as groundwater level and nutrient availability. Due to the high spatial and temporal variability of such environmental drivers, it is hard to make good predictions of CH4 emissions in the context of land-use changes. Here, we used plant species composition as a stable integrator of environmental drivers of CH4 emissions. We used weighted averaging regression and calibration to make a direct link between plant species composition and CH4 flux in an effort to predict values of CH4 emission for a land-use gradient in two extensive peatland sites. Our predicted CH4 emissions showed good fit with observed values. Additionally, we showed that a quick characterization of vegetation composition, by the dominant species only, provides equally good predictions of CH4 emissions. The use of mean groundwater level alone for predicting emissions showed the same predictive power as our models. However, water level showed strong variability in time. Furthermore, the inverse relationship between water level and CH4 emission can lead to higher errors in predictions at sites with higher CH4 emission. The performance of our model was comparable with those of mechanistic models developed for natural wetland ecosystems. However, such mechanistic models require complex input parameters that are rarely available. We propose the use of plant species composition as a simple and effective alternative for deriving predictions of CH4 emissions in peatlands in the context of land-use change.

Canopy composition influencing plant patch dynamics in a Brazilian sandy coastal plain

Competition and predation have often been referred to as key forces regulating community structure. However, in the last decade great attention has been paid to the structuring role of positive interactions between plants, which occur when the presence of one species enhances fitness, survival or growth of another (Bruno et al . 2003, Callaway et al . 2002). Positive and negative interactions are unlikely to occur separately in nature (Brooker & Callaghan 1998, Holmgren et al . 1997), and the overall importance of positive interactions on community structure tends to be higher in resource-poor environments (Callaway et al . 2002). Moreover, this balance can be subjected to spatial and temporal shifts (Callaway 1998, Morris & Wood 1989, Tielborger & Kadmon 1997) linked with plant ontogenetic development and/or changes on resource availability (see Callaway & Walker 1997).

On the need for phylogenetic ‘corrections’ in functional trait-based approaches

There is considerable uncertainty about if, and when, phylogenetic information is needed to answer various ecological questions about trait-based ecological studies. It has been recommended that both functional and phylogenetic information should be combined, and some researchers have even suggested that functional information for species should be ‘corrected’ because species are not phylogenetically independent. Here, we address these issues by identifying key types of questions in functional trait-based ecology and discussing the utility of phylogenetic information for answering them, either as a correction or in combination with functional traits. Phylogenetic analyses are identified as essential to answer questions related to the evolution of adaptations to abiotic and biotic conditions. However, we argue that phylogenetic information is not always relevant for functional trait studies, and should not be incorporated into ecological analyses without clear justification. Phylogenetic relatedness between species should not be considered a bias to be corrected, but rather an evolutionary signal that allows results to be interpreted at different evolutionary scales. Furthermore, if traits are conserved, phylogeny can be used as a proxy for missing information on traits and functional trait diversity. We conclude by providing guidelines on when to apply, and how to interpret, results obtained using phylogenetic information for a variety of ecological questions linked to functional traits.

Clusia as Nurse Plant

The nurse-plant syndrome (see Franco and Nobel 1989) takes place when plant species shelter seedlings, young and/or adult individuals of other species through their ontogeny. The nurse-plant might then enhance fitness, survival and/or growth of associated species (Callaway et al. 2002; Bruno et al. 2003). However, positive and negative interactions are unlikely to occur separately in nature (Holmgren et al. 1997; Brooker and Callaghan 1998; Dickie et al. 2005). This balance is affected by spatial and temporal shifts (Morris and Wood 1989; Tielborger and Kadmon 1997; Callaway 1998) related to plant ontogenetic development and/or changes in resource availability (Callaway and Walker 1997). For instance, the overall importance of positive interactions on community structure, such as the nurse-plant syndrome, is claimed to be higher in resource-poor environments (Callaway et al. 2002; Lortie and Callaway 2006).

Exotic or not, leaf trait dissimilarity modulates the effect of dominant species on mixed litter decomposition

It has long been recognized that leaf traits exert a crucial control on litter decomposition, a key process for nutrient cycling, and that invading species can greatly alter such soil processes via changes in mixed litter trait composition. Trait effects on ecosystem processes are hypothesized to operate via changes in either dominant trait values in the community (often calculated as community-weighted mean trait values; CWM) or trait functional diversity (dissimilarity between species trait values; FD). Few have studied the effects of these community trait components in tandem due to their interdependence. We studied litter mixture decomposition using three exotic and six native European tree species with a range in litter decomposability, to disentangle the unique and combined roles of CWM and FD in explaining net litter mixture mass loss. We showed that while CWM exerted the strongest effect on mass loss, FD modulated its effects, increasing mass loss in mixtures with low mean decomposability and decreasing mass loss in mixtures with high mean decomposability. Litter species identity and native/exotic status explained relatively little additional variation in mass loss after accounting for CWM and FD. We further showed that alterations to CWM and FD were more important than the replacement of a native species with an exotic counterpart in predicting mass loss. Synthesis: Our results indicate that the effect of adding an exotic or losing a native species on litter decomposition rate can be predicted from how a species alters both CWM and FD trait values. This supports the idea that the repercussions of exotic species on ecosystem processes depends on the extent that introduced species bear novel traits or trait values and so on how functionally dissimilar a species is compared to the existing species in the community.

Disentangling community functional components in a litter-macrodetritivore model system reveals the predominance of the mass ratio hypothesis

Recent investigations have shown that two components of community trait composition are important for key ecosystem processes: (i) the community-weighted mean trait value (CWM), related to the mass ratio hypothesis and dominant trait values in the community, and (ii) functional diversity (FD), related to the complementarity hypothesis and the divergence of trait values. However, no experiments controlling for the inherent dependence between CWM and FD have been conducted so far. We used a novel experimental framework to disentangle the unique and shared effects of CWM and FD in a leaf litter-macrodetritivore model system. We manipulated isopod assemblages varying in species number, CWM and FD of litter consumption rate to test the relative contribution of these community parameters in the decomposition process. We showed that CWM, but also the combination of CWM and FD, is a main factor controlling litter decomposition. When we tested individual biodiversity components separately, CWM of litter consumption rate showed a significant effect on decomposition, while FD and species richness alone did not. Our study demonstrated that (i) trait composition rather than species diversity drives litter decomposition, (ii) dominant trait values in the community (CWM) play a chief role in driving ecosystem processes, corroborating the mass ratio hypothesis, and (iii) trait dissimilarity can contribute in modulating the overall biodiversity effects. Future challenge is to assess whether the generality of our finding, that is, that dominant trait values (CWM) predominate over trait dissimilarity (FD), holds for other ecosystem processes, environmental conditions and different spatial and temporal scales.

Plant-plant associations and population structure of four woody plant species in a patchy coastal vegetation of Southeastern Brazil

Este estudo examinou a estrutura populacional e as associacoes interespecificas entre jovens e adultos de quatro especies arbustivo-arboreas (Andira legalis (Vell.) Toledo, Clusia hilariana Schltdl., Protium icicariba (DC.) Marchand and Vernonia crotonoides Sch. Bip. ex Baker) numa restinga composta por ilhas de vegetacao, no sudeste brasileiro. Foram encontradas 101 ilhas de vegetacao numa grade de 0,5 ha e estas foram divididas em duas distintas classes de tamanho, sendo que ilhas grandes (> 20 m2) contiveram a grande maioria dos individuos adultos das especies estudadas. As especies mais abundantes, P. icicariba (465 individuos) e C. hilariana (312), apresentaram evidencias de ativa regeneracao, enquanto para A. legalis (20) e V. crotonoides (338), esta e possivelmente intermitente ou eventual. Os nichos de regeneracao das quatro especies diferiram, assim como as estrategias de reproducao: por exemplo, 81% das plântulas de C. hilariana foram encontradas dentro de tanques de bromelias enquanto apenas 3% das plântulas de P. icicariba foram encontradas neste habitat. Adicionalmente, 28% dos regenerantes de C. hilariana apresentaram origem vegetativa em contraste com apenas 6% dos regenerantes de P. icicariba. Dentre as associacoes significativas encontradas neste estudo, todas foram positivas. Houve uma associacao positiva entre adultos de C. hilariana e P. icicariba, assim como entre adultos de C. hilariana e jovens de ambas especies. Isso sugere que P. icicariba se estabelece sob o dossel de C. hilariana e mostra a importância de C. hilariana ao gerar area com cobertura vegetal que sera posteriormente ocupada por outras especies lenhosas, o que parece ser um importante processo para a manutencao da diversidade de plantas nesta vegetacao de restinga.