Habitat modification effects on anuran food webs in the Colombian tropical dry forest

Habitat loss and transformation are major threats to biodiversity and ecosystem functioning, but their effects on species interaction are often poorly understood. We evaluated effects of habitat transformation and seasonality on anuran-prey food webs in Colombian dry-forests. We asked whether anthropic transformation (anthropic vs natural) and/or seasonality (dry, minor and major rain seasons) affect predator load on arthropods, the occurrence of energetic bottlenecks, and the diet overlap of anurans. We selected six dry forest sites in the Caribbean of Colombia, sampled anurans, and identified their stomach contents to construct anuran-prey food webs. We show that the global structure of food webs was affected by disturbance and seasonality, but not by their interaction. Prey vulnerability was higher in anthropic habitats. Habitat transformation enhanced diet overlap among predators, but there was not a differential effect of habitat type according to seasonality for network metrics. Our study shows a strong effect of natural vegetation modification in tropical dry forest on anuran-prey food webs, while seasonality did not seem to further mediate these effects

Interactions between wood-rotting fungi (Agaricomycetes) and native and exotic trees from an urban ecosystem (Córdoba, Argentina)

El reemplazo de áreas naturales por zonas urbanizadas afecta la composición de las comunidades arbóreas, generalmente favoreciendo la ocurrencia de especies vegetales exóticas. Esto tendría implicancias directas en la estructuración de las comunidades de hongos patógenos que hospedan estas especies arbóreas. En este trabajo se propuso examinar: a) la estructura de la red de interacciones entre especies del arbolado urbano y los hongos patógenos degradadores de la madera, b) la composición de hongos patógenos en especies nativas y exóticas. Se observó que la red de interacciones mostró un patrón de anidamiento en donde varias especies de hongos patógenos establecen múltiples interacciones con diversas especies arbóreas, tanto nativas como exóticas, mientras que otras establecieron interacciones más específicas. Se observó mayor riqueza de hongos en árboles exóticos en comparación a sus pares nativos. Trece de las especies fúngicas se registraron exclusivamente en árboles exóticos, una exclusivamente en sustrato nativo y las nueve restantes compartieron tanto árboles exóticos como nativos.The replacement of natural areas by urban areas promotes changes in the composition of tree communities, frequently favoring the occurrence of exotic species. This may have direct implications in the structure of pathogenic fungal communities which grow in these hosts. Here we examine: a) the structure of the interaction networks between urban tree species and their pathogenic wood-decay fungi, b) the composition of pathogenic fungi in native and exotic hosts. The interactions network shows a nested pattern where several species of pathogenic fungi establish multiple interactions with various tree species, both native and exotic; while others establish more specific interactions. Richness of pathogenic fungi was higher in exotic trees than in natives. Thirteen fungal species occurred exclusively in exotic hosts, one in natives and the remaining nine species shared both exotic and native hosts.Fil: Cagnolo, Luciano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto Multidisciplinario de Biología Vegetal (p); ArgentinaFil: Heredia, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto Multidisciplinario de Biología Vegetal (p); ArgentinaFil: Morera, Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto Multidisciplinario de Biología Vegetal (p); ArgentinaFil: Robledo, Gerardo Lucio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto Multidisciplinario de Biología Vegetal (p); ArgentinaFil: Urcelay, Roberto Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto Multidisciplinario de Biología Vegetal (p); Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentin

Unprecedented plant species loss after a decade in fragmented subtropical Chaco Serrano forests.

Current biodiversity loss is mostly caused by anthropogenic habitat loss and fragmentation, climate change, and resource exploitation. Measuring the balance of species loss and gain in remaining fragmented landscapes throughout time entails a central research challenge. We resurveyed in 2013 plant species richness in the same plots of a previous sampling conducted in 2003 across 18 forest fragments of different sizes of the Chaco Serrano forest in Argentina. While the area of these forest remnants was kept constant, their surrounding forest cover changed over this time period. We compared plant species richness of both sampling years and calculated the proportion of species loss and gain at forest edges and interiors. As in 2003, we found a positive relationship between fragment area and plant richness in 2013 and both years showed a similar slope. However, we detected a net decrease of 24% of species’ richness across all forest fragments, implying an unprecedentedly high rate and magnitude of species loss driven mainly by non-woody, short-lived species. There was a higher proportion of lost and gained species at forest edges than in forest interiors. Importantly, fragment area interacted with percent change in surrounding forest cover to explain the proportion of species lost. Small forest fragments showed a relatively constant proportion of species loss regardless of any changes in surrounding forest cover, whereas in larger fragments the proportion of species lost increased when surrounding forest cover decreased. We show that despite preserving fragment area, habitat quality and availability in the surroundings is of fundamental importance in shaping extinction and immigration dynamics of plant species at any given forest remnant. Because the Chaco Serrano forest has already lost 94% of its original cover, we argue that plant extinctions will continue through the coming decades unless active management actions are taken to increase native forest areas.publishedVersio

Ecological network complexity scales with area

Larger geographical areas contain more species—an observation raised to a law in ecology. Less explored is whether biodiversity changes are accompanied by a modification of interaction networks. We use data from 32 spatial interaction networks from different ecosystems to analyse how network structure changes with area. We find that basic community structure descriptors (number of species, links and links per species) increase with area following a power law. Yet, the distribution of links per species varies little with area, indicating that the fundamental organization of interactions within networks is conserved. Our null model analyses suggest that the spatial scaling of network structure is determined by factors beyond species richness and the number of links. We demonstrate that biodiversity–area relationships can be extended from species counts to higher levels of network complexity. Therefore, the consequences of anthropogenic habitat destruction may extend from species loss to wider simplification of natural communities.This work was supported by the TULIP Laboratory of Excellence (ANR-10-LABX-41 and 394 ANR-11-IDEX-002-02) to J.M.M., by a Region Midi-Pyrenees project (CNRS 121090) to J.M.M., and by the FRAGCLIM Consolidator Grant (726176) to J.M.M. from the European Research Council under the European Union’s Horizon 2020 Research and Innovation Program. The study was also supported by Spanish MICINN projects CGL2009-12646, CSD2008-0040 and CGL2013-41856 to J.B. and A.R. C.E. was funded through the São Paulo Research Foundation (FAPESP 2015/15172-7). V.A.G.B. was funded by National Funds through FCT—Foundation for Science and Technology under the Project UIDB/05183/2020. W.T. received funding from the ERA-Net BiodivERsA—Belmont Forum, with the national funder Agence National pour la Recherche (FutureWeb: ANR-18-EBI4–0009 and BearConnect: ANR-16-EBI3-0003).Peer reviewe

Habitat fragmentation and food web disassembly

La fragmentación de hábitats, mediada por los cambios en uso de la tierra, constituye una de las principales amenazas a la biodiversidad del planeta. En una comunidad, las especies se encuentran conectadas mediante relaciones tróficas que componen complejas redes de interacción. Debido a esto, los cambios en abundancia o pérdida de especies pueden tener efectos indirectos propagándose e incluso magnificándose a lo largo de las cadenas tróficas. Por lo tanto, entender la forma en que se pierden especies y el efecto de esta pérdida sobre la organización de la comunidad resultante son desafíos urgentes para los ecólogos. En este trabajo evaluamos la relación entre fragmentación de hábitat, extinciones y redes de interacción estudiando los cambios en la estructura de redes tróficas de plantas, insectos herbívoros y sus parasitoides en bosques del centro de Argentina. Encontramos que las redes son afectadas por una reducción en su tamaño, y aumentos de la intensidad relativa de interacción y la conectancia a medida que se reduce el área de bosque.Habitat fragmentation, mediated by land use change, is one of the major threats to biodiversity. In a community, species are connected by trophic relationships that comprise complex networks of interaction. Because of this, changes in abundance or loss of species may have indirect effects that spread and even magnify along the food chain. Therefore, understanding how species are lost and how these losses affect community organization are urgent challenges for ecologists. We evaluated the relationship between fragmentation and network structure by studying the changes in the structure of food webs of plant, insect herbivores and their parasitoids in forests of central Argentina. We found that the networks were affected by a reduction in size, and increased in relative interaction intensity and connectance as the forest area was reduced.Este trabajo ha sido financiado por National Geographic Society, Consejo Nacional de Investigaciones Científicas y Técnicas de Argentina, Agencia Nacional de Promoción de Ciencia y Tecnología, Secretaría de Ciencia y Técnica - Universidad Nacional de Córdoba y Agencia Córdoba Ciencia

Keystones in a Tangled Bank: Ecological network studies highlight the importance of individual species to community conservation

In the past decade, ecologists have increasingly applied complex network theory (1, 2) to ecological interactions, both in entire food webs (3) and in networks representing ecological interactions, especially those between plants and their animal pollinators or seed dispersers (4). How important are individual species to the maintenance of such ecological networks? On page 1489 of this issue, Stouffer et al. (5) analyze terrestrial, freshwater, and marine food webs to infer the contributions of individual species to network stability. In a related field study on page 1486 of this issue, Aizen et al. (6) explore plant and pollinator webs on a landscape scale. Using a different field study design, Pocock et al. (7) recently focused on a local community in which several webs of different kinds of interactions and organisms form a composite network.Fil: Lewinsohn, Thomas. Universidade Estadual de Campinas; BrasilFil: Cagnolo, Luciano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Instituto Multidisciplinario de Biología Vegetal (p); Argentin

The network structure of myrmecophilic interactions

1. Ants establish mutualistic interactions involving a wide range of protective relationships (myrmecophily), in which they provide defence against enemies and partners provide food rewards and/or refuge. Although similar in the general outcome, myrmecophilic interactions differ in some characteristics such as quantity and quality of rewards offered by partners which may lead to different specialisation levels and, consequently, to different network properties. 2. The aim of this study was to identify structural patterns in myrmecophilic interaction networks, focusing on aspects related to specialisation: network modularity, nestedness and taxonomic relatedness of interaction ranges. To achieve this, a database of networks was compiled, including the following interactions: ants and domatia-bearing plants (myrmecophytes); ants and extrafloral nectary-bearing plants (EFNs); ants and floral nectary-bearing plants (FNs); ants and Lepidoptera caterpillars; and ants and Hemiptera. 3. Myrmecophilic networks differed in their topology, with ant–myrmecophyte and ant–Lepidoptera networks being similar in their structural properties. A continuum was found, ranging from highly modular networks and phylogenetically structured interaction ranges in ant–myrmecophyte followed by ant–Lepidoptera networks to low modularity and taxonomically unrelated interaction ranges in ant–Hemiptera, EFN and FN networks. 4. These results suggest that different network topologies may be found across communities of species with similar interaction types, but also, that similar network topologies can be achieved through different mechanisms such as those between ants and myrmecophytes or Lepidoptera larvae. This study contributes to a generalisation of myrmecophilic network patterns and a better understanding of the relationship between specialisation and network topology.Fil: Cagnolo, Luciano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Tavella, Julia Rita. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentin

Does fire disturbance affect ant community structure? Insights from spatial co-occurrence networks

The coexistence of several species involves a complex mix of positive and negative interactions that can be represented as networks. As much as other ecological features, patterns of multispecies co-occurrence are susceptible to anthropogenic disturbance. In ant communities, wildfires may enhance competitive interactions by benefiting active, aggressive species, and by increasing encounter probabilities through decreased space availability. We explored ant co-occurrence patterns by analysing the macro and microscopic structure of their interaction networks in burned and unburned habitats. We built co-occurrence networks using significant aggregations and segregations between species pairs as positive and negative interactions, respectively. We described aggregate network properties and microscopic structural changes by comparing species and interactions turnover between burned and unburned sites. We found no differences in the macroscopic structure of co-occurrence networks between different fire regimes. However, we detected changes in the composition of both species and negative interactions. Interaction turnover between networks of different habitats was mostly explained by rewiring of interactions between shared species rather than by species replacement. Our results reflected changes in ant communities in response to fire although there were no changes in global structural patterns. These changes in species and negative interactions suggest modifications in species roles translated into changes in the spatial distribution of ant species. The analysis of species co-occurrence networks is a useful tool to detect and visualize patterns in ant communities and to understand the mechanisms underlying the effects of disturbance on biodiversity.Fil: Tavella, Julia Rita. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Cagnolo, Luciano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentin

Landscape connectivity explains interaction network patterns at multiple scales

Under a metacommunity framework, the spatial configuration of habitat fragments could determine local community structure. Yet, quantifying fragment connectivity is challenging, as it depends on multiple variables at several geographical scales. We assessed the extent to which fragment connectivity and area explain patterns in interaction structure among four herbivore guilds and their host plants in a metacommunity. We propose an integrative connectivity metric including geographic distance, neighboring fragment area and similarity in resource composition as an extension of Hanski’s classic metric. We then used nonlinear models to assess whether fragment connectivity and area predicted link richness and similarity in link composition. We found that link richness was always negatively related to connectivity but at different geographic scales depending on the herbivore guild. In contrast, while link composition was also related to connectivity, the direction and strength of this relationship varied among herbivore guilds and type of link composition (qualitative or quantitative). Furthermore, focal fragment area was not an important determinant of interaction diversity in local communities. Our findings emphasize resource similarity as a novel dimension of fragment connectivity relevant in explaining interaction diversity patterns in natural trophic networks.Fil: Santos, Micaela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; ArgentinaFil: Cagnolo, Luciano. Universidad Nacional de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Roslin, Tomas. University of Helsinki; Finlandia. Swedish University of Agricultural Sciences; SueciaFil: Marrero, Hugo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; ArgentinaFil: Vazquez, Diego P.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentin