Geographical variation of multiplex ecological networks in marine intertidal communities

Understanding the drivers of geographical variation in species distributions, and the resulting community structure, constitutes one of the grandest challenges in ecology. Geographical patterns of species richness and composition have been relatively well studied. Less is known about how the entire set of trophic and non‐trophic ecological interactions, and the complex networks that they create by gluing species together in complex communities, change across geographical extents. Here, we compiled data of species composition and three types of ecological interactions occurring between species in rocky intertidal communities across a large spatial extent (~970 km of shoreline) of central Chile, and analyzed the geographical variability in these multiplex networks (i.e., comprising several interaction types) of ecological interactions. We calculated nine network summary statistics common across interaction types, and additional network attributes specific to each of the different types of interactions. We then investigated potential environmental drivers of this multivariate network organization. These included variation in sea surface temperature and coastal upwelling, the main drivers of productivity in nearshore waters. Our results suggest that structural properties of multiplex ecological networks are affected by local species richness and modulated by factors influencing productivity and environmental predictability. Our results show that non‐trophic negative interactions are more sensitive to spatially structured temporal environmental variation than feeding relationships, with non‐trophic positive interactions being the least labile to it. We also show that environmental effects are partly mediated through changes in species richness and partly through direct influences on species interactions, probably associated to changes in environmental predictability and to bottom‐up nutrient availability. Our findings highlight the need for a comprehensive picture of ecological interactions and their geographical variability if we are to predict potential effects of environmental changes on ecological communities

INTERTIDAL BIODIVERSITY IN CENTRAL CHILE REVISTA CHILENA DE HISTORIA NATURAL

ABSTRACT Along the coast of central Chile, geographic trends of diversity have been inferred from literature compilations and museum collections based on species range limits for some taxonomic groups. However, spatially-intensive fieldbased assessments of macrobenthic species richness are largely missing. Over the course of a multiyear study (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005), we characterized latitudinal patterns of rocky intertidal diversity at 18 sites along the coast of central Chile (29-36º S). At each site, the number of sessile and mobile macrobenthic species was quantified in 0.25 m 2 quadrats. Two estimators of local (alpha) diversity were used: observed local species richness, calculated from the asymptote of a species-rarefaction curve, and the Chao2 index, which takes into account the effect of rare species on estimates of local richness. We identified a total of 71 species belonging to 66 genera for a total of 86 taxa. The most diverse groups were herbivorous mollusks (27 taxa) and macroalgae (43 taxa). Diversity showed a complex spatial pattern with areas of high species richness interspersed with areas of low richness. In accordance with previous work, we found no trend in the number of herbivorous mollusks and an inverse and significant latitudinal gradient in the number of algal species. Our results highlight the need for taxonomically diverse assessments of biodiversity of the dominant taxa that conform intertidal communities

More than a meal… integrating non-feeding interactions into food webs

Organisms eating each other are only one of many types of well documented and important interactions among species. Other such types include habitat modification, predator interference and facilitation. However, ecological network research has been typically limited to either pure food webs or to networks of only a few (<3) interaction types. The great diversity of non-trophic interactions observed in nature has been poorly addressed by ecologists and largely excluded from network theory. Herein, we propose a conceptual framework that organises this diversity into three main functional classes defined by how they modify specific parameters in a dynamic food web model. This approach provides a path forward for incorporating non-trophic interactions in traditional food web models and offers a new perspective on tackling ecological complexity that should stimulate both theoretical and empirical approaches to understanding the patterns and dynamics of diverse species interactions in nature.Keywords: Ecosystem engineering, Non-trophic interactions, Ecological network, Food web, Interaction modification, Facilitation, Trophic interaction

Predator traits determine food-web architecture across ecosystems

Predator–prey interactions in natural ecosystems generate complex food webs that have a simple universal body-size architecture where predators are systematically larger than their prey. Food-web theory shows that the highest predator–prey body-mass ratios found in natural food webs may be especially important because they create weak interactions with slow dynamics that stabilize communities against perturbations and maintain ecosystem functioning. Identifying these vital interactions in real communities typically requires arduous identification of interactions in complex food webs. Here, we overcome this obstacle by developing predator-trait models to predict average body-mass ratios based on a database comprising 290 food webs from freshwater, marine and terrestrial ecosystems across all continents. We analysed how species traits constrain body-size architecture by changing the slope of the predator–prey body-mass scaling. Across ecosystems, we found high body-mass ratios for predator groups with specific trait combinations including (1) small vertebrates and (2) large swimming or flying predators. Including the metabolic and movement types of predators increased the accuracy of predicting which species are engaged in high body-mass ratio interactions. We demonstrate that species traits explain striking patterns in the body-size architecture of natural food webs that underpin the stability and functioning of ecosystems, paving the way for community-level management of the most complex natural ecosystems

Benthic-pelagic coupling : rocky intertidal communities and nearshore oceanographic conditions across multiple scales

Includes bibliographical references (leaves 111-148).In Chapter 1, I characterize geographic patterns in rocky intertidal communities across 6° of latitude along the west coast of South Africa and examine the spatial structure of functional group biomass in relation to wave action and upwelling intensity. Despite between-habitat differences in biomass, most functional groups showed similar regional trends in exposed and sheltered habitats, but weaker non-significant between-habitat associations were observed when considering differences due to site. Divese geographic trends were observed, with only specialized kelp-trapping limpets showing a smoothly decreasing trend with latitide. Abrupt changes in the abundance of several species were observed at about 32° or near 34.5° S. Correlations between functional groups were strongest in the low (exposed) and mid (sheltered) shores, and supported the possibility that species interactions, particularly (1) competitive dominance by filter feeders and gardening limpets and (2) habitat facilitation by filter feeders partially account for local differences in functional-group abundances. Nearshore oceanographic conditions were characterized using satellite-measured sea surface temperature (SST), verification by in situ loggers, and analysis of Offshore Ekman Transport (OET) indices. A clear discontinuity at about 32° S partitioned the coast into a northern region characterized by consistenly strong and spatially homogenous upwelling, and a southern region distinguished by significant mesoscale variation in seasonal upwelling intensity among sites, with clear upwelling centers alternating with "downstream" areas only weakly influenced by upwelling. Functional group relationships with SST differed between north and south regions. Local abundances were generally more variable in the south, where greater biomass of ephemeral and corticated macroalgae, as well specialized gardening and kelp-trapping limpets, were associated with upwelling centers. In contrast, high-shore filter-feeder and predator biomasses were significantly greater at downstream sites. These results suggest that oceanographic discontinuities around 32° S may frame community dynamics and that upwelling intensity influences community structure and generates regular spatial differences in interaction webs along the South West Cape. This study represents the critical first step to identifying spatial scales at which processes regulate communities, and provides a series of testable hypotheses that can be evaluated by experimental comparative approaches

Functional community structure of shallow hard bottom communities at Easter Island (Rapa Nui): Estructura funcional de comunidades que habitan sobre los fondos duros de Isla de Pascua (Rapa Nui)

Important, often abrupt, and irreversible shifts associated with the degradation of ecosystem functioning and services are increasingly commonplace. Thus, a trait-based view of communities may be more insightful than that based solely on species composition, especially when inferring ecological responses to environmental change. This underscores the importance and urgency of establishing benchmarks against which future community changes and functional structure can be evaluated. As a first step toward setting these baselines and their current spatial variability, we here describe geographic and among-habitat patterns in the functional structure of shallow hard bottom communities, including fish assemblages, across the northeast and west coasts of Rapa Nui. We also document temporal patterns of change in dominant benthic functional groups that have taken place over the past 15 years at selected sites on this isolated Pacific island. Generally weak vertical zonation patterns were observed, with most striking differences due to the paucity of branching pocilloporid corals in shallow waters(15 m) habitats, with contrasting recovery. These results suggest depth-dependent disturbance regimes that differ in types and frequency of events, as well as capacity to recover. Overall, our results highlight the apparent resilience of the current system and provide a first-cut benchmark as to where management subsystems might be prescribed so as to spatially match ecosystem characteristics

Annual Termperature Anomaly Trends Correlate with Coral Reef Trajectory Across the Pacific

The future survival of coral reefs depends on the envelope of critical climatic conditions determining the severity of impacts on the ecosystem. While coral health is strongly determined by extreme heat events, that lead to bleaching and often death, chronic “heat loading” may also disadvantage corals by making them more susceptible to, for example, diseases. On the other hand, it has been shown that coral living in hotter areas have higher bleaching thresholds and may be affected by less mortality at extreme events. This level at which heat anomalies lead to coral mortality varies widely across oceans, from ~31 deg C across the Caribbean to ~32 deg C in the Great Barrier Reef to 37.5 deg C in the Persian/Arabian Gulf. Thus, there clearly exists local adaptation and the extremes required to kill reefs strongly vary among regions. This could be be interpreted as suggesting that as long as bleaching temperatures are not reached, increased overall heat content expressed by a positive annual thermal anomaly, might actually foster coral resilience. Is there evidence for or against such an argument? Bleaching events have been occurring worldwide with variable recurrence and variable subsequent recovery. Despite demonstrated adaptation to higher-than-usual mean summer temperatures, reefs in the Arabian Gulf and the Red Sea are on a declining trajectory. This coincides with consistent warming in the region. Mean annual anomalies of ocean temperature (since 1870) and atmospheric temperatures (since 1950) increase throughout the region. Since 1994 (Red Sea) and 1998 (southern Arabian Gulf) all mean annual anomalies have been positive and this period has coincided with repeated, severe bleaching events. In the Eastern Pacific (Galapagos and Easter Island), the trend of mean annual temperature anomalies has been declining and coral cover has been increasing. Thus, trends in coral cover and mean annual anomaly are negatively correlated in both regions. Despite strong impacts due to bleaching in 1983 and 1998, and increasing variance in anomalies (both positive and negative) the E-Pacific presently maintains an upward trend in coral cover and colony frequency. In the Red Sea , variance in anomalies increased but exclusively towards positive values. In the Gulf, variance declined towards stronger and only positive anomalies. In both regions, this raised thermal envelope is associated with reef decline. This is most dramatic in the Gulf, with six bleaching events since 1996, but also obvious in the Red Sea (bleaching in 1998, 2005 and 2010). Both Gulf and Red Sea suffer also from other mortality factors, such as diseases and predator outbreaks. Decline in reef health is therefore not uniquely linked to bleaching, but other mortality factors are also linked to changes in the thermal envelope. Chronic effects of increased average temperatures seem to define a reef trajectory more closely than the effects of individual, albeit strong, episodic disturbances

Figure S5 data

Outgoing links probabilities of each cluster (matrix 14x14