Raphaël Proulx

Habitat filtering and niche differentiation jointly explain species relative abundance within grassland communities along fertility and disturbance gradients

Deterministic niche-based processes have been proposed to explain species relative abundance within communities but lead to different predictions: habitat filtering (HF) predicts dominant species to exhibit similar traits while niche differentiation (ND) requires that species have dissimilar traits to coexist. Using a multiple trait-based approach, we evaluated the relative roles of HF and ND in determining species abundances in productive grasslands. Four dimensions of the functional niche of 12 co-occurring grass species were identified using 28 plant functional traits. Using this description of the species niche, we investigated patterns of functional similarity and dissimilarity and linked them to abundance in randomly assembled six-species communities subjected to fertilization/disturbance treatments. Our results suggest that HF and ND jointly determined species abundance by acting on contrasting niche dimensions. The effect of HF decreased relative to ND with increasing disturbance and decreasing fertilization. Dominant species exhibited similar traits in communities whereas dissimilarity favored the coexistence of rare species with dominants by decreasing inter-specific competition. This stabilizing effect on diversity was suggested by a negative relationship between species over-yielding and relative abundance. We discuss the importance of considering independent dimensions of functional niche to better understand species abundance and coexistence within communities.

Diversity Promotes Temporal Stability across Levels of Ecosystem Organization in Experimental Grasslands

The diversity–stability hypothesis states that current losses of biodiversity can impair the ability of an ecosystem to dampen the effect of environmental perturbations on its functioning. Using data from a long-term and comprehensive biodiversity experiment, we quantified the temporal stability of 42 variables characterizing twelve ecological functions in managed grassland plots varying in plant species richness. We demonstrate that diversity increases stability i) across trophic levels (producer, consumer), ii) at both the system (community, ecosystem) and the component levels (population, functional group, phylogenetic clade), and iii) primarily for aboveground rather than belowground processes. Temporal synchronization across studied variables was mostly unaffected with increasing species richness. This study provides the strongest empirical support so far that diversity promotes stability across different ecological functions and levels of ecosystem organization in grasslands.

Googling trends in conservation biology.

Web-crawling approaches, that is, automated programs data mining the internet to obtain information about a particular process, have recently been proposed for monitoring early signs of ecosystem degradation or for establishing crop calendars. However, lack of a clear conceptual and methodological framework has prevented the development of such approaches within the field of conservation biology. Our objective was to illustrate how Google Trends, a freely accessible web-crawling engine, can be used to track changes in timing of biological processes, spatial distribution of invasive species, and level of public awareness about key conservation issues. Google Trends returns the number of internet searches that were made for a keyword in a given region of the world over a defined period. Using data retrieved online for 13 countries, we exemplify how Google Trends can be used to study the timing of biological processes, such as the seasonal recurrence of pollen release or mosquito outbreaks across a latitudinal gradient. We mapped the spatial extent of results from Google Trends for 5 invasive species in the United States and found geographic patterns in invasions that are consistent with their coarse-grained distribution at state levels. From 2004 through 2012, Google Trends showed that the level of public interest and awareness about conservation issues related to ecosystem services, biodiversity, and climate change increased, decreased, and followed both trends, respectively. Finally, to further the development of research approaches at the interface of conservation biology, collective knowledge, and environmental management, we developed an algorithm that allows the rapid retrieval of Google Trends data.

Measuring Protected‐Area Isolation and Correlations of Isolation with Land‐Use Intensity and Protection Status

Protected areas cover over 12% of the terrestrial surface of Earth, and yet many fail to protect species and ecological processes as originally envisioned. Results of recent studies suggest that a critical reason for this failure is an increasing contrast between the protected lands and the surrounding matrix of often highly altered land cover. We measured the isolation of 114 protected areas distributed worldwide by comparing vegetation-cover heterogeneity inside protected areas with heterogeneity outside the protected areas. We quantified heterogeneity as the contagion of greenness on the basis of NDVI (normalized difference vegetation index) values, for which a higher value of contagion indicates less heterogeneous land cover. We then measured isolation as the difference between mean contagion inside the protected area and mean contagion in 3 buffer areas of increasing distance from the protected-area border. The isolation of protected areas was significantly positive in 110 of the 114 areas, indicating that vegetation cover was consistently more heterogeneous 10-20 km outside protected areas than inside their borders. Unlike previous researchers, we found that protected areas in which low levels of human activity are allowed were more isolated than areas in which high levels are allowed. Our method is a novel way to assess the isolation of protected areas in different environmental contexts and regions.

Disentangling the environmental‐heterogeneity–species‐diversity relationship along a gradient of human footprint

Decades of study have attempted to define a generalized environmental-heterogeneity-biodiversity (EH-BD) relationship, with the traditional MacArthurian niche-based hypothesis remaining as the dominant reference point; i.e., increasing heterogeneity promotes biodiversity by increasing resource opportunities. However, studies have frequently reported negative or nonsignificant relationships. In a vast majority of them, environmental heterogeneity was defined along a gradient of increasing randomness, toward complete disorder. A new conceptual framework could help to reconcile the array of observed relationships. Using an extensive literature review, we test a conceptual framework proposing that the direction of environmental-heterogeneity-biodiversity relationships is contingent on the level of human footprint to which an ecosystem is subjected (the anthropocline). The results reveal that highly modified and seminatural ecosystems are characterized by a dominance of positive and negative EH-BD relationships, respectively, whereas natural ecosystems show mixed responses. Out of this novel framework arises the revised perspective that natural ecosystems are typified, not by maximal or minimal, but by intermediate levels of environmental heterogeneity.

Detecting human-driven deviations from trajectories in landscape composition and configuration

While landscape trajectories are increasingly used for tracking change in processes such as agricultural intensification and urbanization, analyses that combine environmental and human disturbances remain scarce. The aim of this study was to investigate the relationship between Shannon evenness, a measure of landscape composition, and spatial contagion, a measure of landscape configuration, within sixteen Canadian regions covering a gradient of land-uses and human disturbances: natural, semi-natural, urban, and agricultural. The agricultural regions showed generally lower variation in contagion and evenness and overall lower contagion values (smaller patches), leading to steeper contagion-evenness slopes than in the other region categories. In addition, the sampled agricultural regions were much more similar to each other than were the sampled regions within each of the other three region categories. These results indicate that the process of agricultural development (at least in western Canada) leads to a reduction in pattern variation and an alteration of the expected relationships among pattern metrics in agricultural regions. This possibility is supported by a neutral model of patch dynamics, suggesting that the characteristic scale of disturbances is a generic structuring process of landscape trajectories.

Three-dimensional metrics for the analysis of spatiotemporal data in ecology

A suite of simple metrics that can be used to analyse three-dimensional data sets is presented. We show how these metrics can be applied to raster-based, ecological mosaics sampled over uniform time intervals, such as might be obtained from a series of photographs or from repeated spatial sampling in the field. In these analyses, the concept of a 2D landscape “patch” is replaced by a 3D space–time “blob”. The structure of a dataset can be analysed via the characterisation of blobs, using a number of simple composition and configuration metrics. The use of different metrics, including modified versions of some common landscape metrics such as contagion, that describe the distribution of blobs in space and time, is demonstrated using both model and empirical data. With the increasing availability of spatiotemporal data sets in ecology, such three-dimensional metrics may be indispensable tools for the detection and characterization of landscape change in the context of human and naturally caused disturbances.

Physiological performance of two forms of lacustrine brook charr, Salvelinus fontinalis, in the open-water habitat

Although morphological differences among ecotypes have often been observed, little is known about the adaptive value of these differences in terms of the relative performance of individuals. The first objective of this study was to compare specific growth rates, muscle proteins, lipids, and water content in the muscles and digestive tracts of littoral and pelagic brook charr (1+) when individuals of both forms were restricted to feeding on zooplankton for 76 days, in pelagic enclosures of a Canadian Shield lake. The second objective was to determine if differences in the physiological performance of experimental fish were related to differences in their morphology. The specific growth rate was low and did not differ significantly between littoral and pelagic individuals at the end of the experiment. However, littoral individuals lost more lipids and had lower muscle protein content than pelagic fish at the end of the experiment. The pectoral fin was longer in littoral individuals than in pelagic ones. Furthermore, the biochemical discriminant scores of individuals were marginally correlated to those of morphology. Based on a comparison of their proximate tissue composition, our results suggest that trophic diversification is adaptive in brook charr because littoral individuals exhibited lower physiological performance than pelagic ones when restricted to feeding in the pelagic zones. In addition, our results support that morphological descriptors are related to physiological performance. This study is one of the first field attempts to relate differences in trophic morphology of a fish species to physiological performance.

Riverscape heterogeneity explains spatial variation in zooplankton functional evenness and biomass in a large river ecosystem

Ecologists have long focused on local-scale phenomena (i.e. local environment variables) and assumed that spatial processes were unimportant factors influencing both the community structure and the functional diversity of aquatic communities. In this paper we used zooplankton assemblages in a typical large river (St. Lawrence River) as a biological model to examine the roles of (1) local environmental conditions (physicochemical characteristics of the water column), (2) broad-scale connectivity (a proxy for dispersion potential), and (3) habitat heterogeneity (a proxy for niche diversity) on the structure and the diversity of lotic communities. Together, these three sets of descriptors explained respectively 52, 49 and 59 % of the variation in zooplankton total biomass, functional diversity and community structure. After partialling out the roles of local environmental conditions and broad-scale connectivity, we demonstrated that habitat heterogeneity alone is a key driver of zooplankton total biomass and functional evenness at the riverscape level. In homogeneous and temporally stable habitats, zooplankton communities had higher biomass and functional evenness but lower species richness. Conversely, zooplankton had lower biomass and higher species richness in heterogeneous and unstable habitats, suggesting that zooplankton species can coexist because disturbances prevent competitive exclusion from occurring. This is the first study to reveal how local environmental conditions, spatial connectivity and habitat heterogeneity operate jointly to determine the functional diversity and structure of aquatic communities in a natural ecosystem.

A multivariate analysis for evaluating the environmental and economical aspects of agroecosystem sustainability in central Italy.

Over the past century farming activity has intensified worldwide, characterized by an increasing dependence on external inputs and on land conversion. Although the intensification of agriculture has increased productivity, the sustainability of agroecosystems has also been compromised. The objective of this study is to build multivariate relationships between farm structural characteristics and farm performance to highlight the relative costs and benefits of four main farming systems in Central Italy: organic, conventional, mixed and non-mixed farms. Results show that the relationship between cropping diversity and agroecological sustainability is associated to a mixed versus non-mixed farm management dichotomy, not to organic or conventional farming practices. The presence of livestock appears to have played an important role as an economic lever for diversifying the farm cropping system.