1.There has been an intense focus on the response of species to environmental changes and more recently the interactions of species have been examined in a similar way in order to understand the stability of entire communities and networks of interacting species. As a consequence, ecological networks have been placed in spatial and temporal contexts in order to reveal what may drive network variability. Understanding the spatial and temporal variability of ecological networks, and in particular the underlying forces facilitating changes, seems pertinent in our attempts to understand and anticipate how ecological networks may vary and respond to future environmental scenarios.

2.Network variability has been studied at widely differing temporal and spatial scales. For example, studies exploring temporal variability ranges from within-season comparisons to comparisons over vast geological timespans, and the spatial extent ranges from the scale of a single pond to global analyses. Here we highlight the outcomes from such studies and emphasize the identified mechanisms driving spatio-temporal variability in ecological networks. Specifically, we describe how ecological networks vary over different temporal (years, centuries and millennia) and spatial (local, regional and global) scales, discuss how this variability is monitored, and identify potential future directions.

3.Present knowledge allows some tentative generalizations. First, ecological networks tend to exhibit considerable spatial and temporal stability in several macroscopic features (e.g. connectance, nestedness), but studies also show that macroscopic features may changes e.g. in relation to mass extinction or steep environmental gradients. Second, microscopic features (e.g. individual specialization levels, species roles, and partner affiliations), albeit less studied, seem to show strong variability, and in several cases microscopic instability co-occur with macroscopic stability. We therefore recommend a stronger focus on this macro-micro interplay, and list ideas (e.g. temporal species centrality measures, and interaction phenologies), towards expanding the microscopic toolbox of network ecologists.

This article is protected by copyright. All rights reserved.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/1365-2435.12710

Ecological networks in motion: Micro- and macroscopic variability across scales

Economic valuation of ecosystem services from secondary tropical forests: trade-offs and implications for policy making

Plants emit an extraordinary diversity of chemicals that provide information about their identity and mediate their interactions with insects. However, most studies of this have focused on a few model species in controlled environments, limiting our capacity to understand plant-insect chemical communication in ecological communities. Here, by integrating information theory with ecological and evolutionary theories, we show that a stable information structure of plant volatile organic compounds (VOCs) can emerge from a conflicting information process between plants and herbivores. We corroborate this information “arms race” theory with field data recording plant-VOC associations and plant-herbivore interactions in a tropical dry forest. We reveal that plant VOC redundancy and herbivore specialization can be explained by a conflicting information transfer. Information-based communication approaches can increase our understanding of species interactions across trophic levels.

/pdf/information-arms-race-explains-plant-herbivore-chemical-2eybwv87wc.pdf

Information arms race explains plant-herbivore chemical communication in ecological communities

Summary
1.Plants emit volatile blends specific to particular herbivore interactions, which predators and parasitoids learn to associate with prey, increasing herbivore mortality and thereby plant fitness in a phenomenon termed indirect defense.

2.Herbivore-induced plant volatile blends commonly include both rapid, transient green leaf volatiles (GLVs) and delayed, enduring sesquiterpenes. A few laboratory studies indicate that insects can use plant volatiles to time behavior, but it is not known whether and how the temporal dynamics of plant volatile blends influence their function in indirect defense.

3.We characterized the activity of the native herbivores Manduca sexta and Tupiocoris notatus and their predators, Geocoris spp., on their host plant Nicotiana attenuata in their natural habitat. Diurnal predator activity only partially overlapped with variable herbivore activity, and herbivore attack at the beginning or end of the photophase elicited plant volatile blends with distinct GLV and sesquiterpene profiles.

4.In field trials, day-active Geocoris spp. predators preferred morning- over evening-typical GLV blends. Using plants genetically transformed so as to be unable to produce specific volatiles, we found that GLVs increased predation after dawn elicitations, whereas sesquiterpenes increased predation after dusk elicitations in field trials.

5.We conclude that predators respond to temporal differences in plant volatile blends, and that the different dynamics of specific volatiles permit effective indirect defense despite variable herbivore activity in nature.

This article is protected by copyright. All rights reserved.

https://besjournals.onlinelibrary.wiley.com/doi/epdf/10.1111/1365-2435.12947

Herbivore-induced volatile blends with both “fast” and “slow” components provide robust indirect defence in nature

Tropical forests are undergoing a biodiversity crisis including defaunation processes. Structure and function of biotic communities in disturbed ecosystems can be assessed with network analyses of interspecific interactions. In a disturbed tropical forest we studied the network of interactions between fruiting plants and three groups of frugivorous animals, determining the structure, modular roles of species and the robustness of the network under simulated extinction scenarios based on species strength (SS) (relevance), species role (SR) (connectivity) and body size (vulnerability). We recorded 5,347 interactions between 63 frugivore and 60 plant species. The network had a modular structure with four modules: (1) plants with exposed fruits consumed by bats; (2) plants with juicy fruits consumed by larger birds; (3) plants with dry high-lipid-content fruits consumed by migratory birds; and (4) generalist plants consumed by several frugivores (three guilds). Robustness of the network was lower when species with high SS or important connectivity roles (i.e., module hubs) were lost first; when larger animals were lost first the network was more robust than in the other scenarios. Our results suggest that modularity may protect disturbed communities against species loss. We provide bases for developing ecologically-sound measures for the conservation of ecological interactions in anthropogenic landscapes.

https://bioone.org/journals/ecoscience/volume-25/issue-3/11956860.2018.1446284/Modularity-and-Robustness-of-a-Plant-Frugivore-Interaction-Network-in/10.1080/11956860.2018.1446284.pdf

Modularity and robustness of a plant-frugivore interaction network in a disturbed tropical forest

Despite the dynamic nature of ecological interactions, most studies on species networks offer static representations of their structure, constraining our understanding of the ecological mechanisms involved in their spatio-temporal stability. This is the first study to evaluate plant-herbivore interaction networks on a small spatio-temporal scale. Specifically, we simultaneously assessed the effect of host plant availability, habitat complexity and seasonality on the structure of plant-herbivore networks in a coastal tropical ecosystem. Our results revealed that changes in the host plant community resulting from seasonality and habitat structure are reflected not only in the herbivore community, but also in the emergent properties (network parameters) of the plant-herbivore interaction network such as connectance, selectiveness and modularity. Habitat conditions and periods that are most stressful favored the presence of less selective and susceptible herbivore species, resulting in increased connectance within networks. In contrast, the high degree of selectivennes (i.e. interaction specialization) and modularity of the networks under less stressful conditions was promoted by the diversification in resource use by herbivores. By analyzing networks at a small spatio-temporal scale we identified the ecological factors structuring this network such as habitat complexity and seasonality. Our research offers new evidence on the role of abiotic and biotic factors in the variation of the properties of species interaction networks.

/pdf/evaluating-the-spatio-temporal-factors-that-structure-5gp2q5lvyf.pdf

Evaluating the Spatio-Temporal Factors that Structure Network Parameters of Plant-Herbivore Interactions

PREMISE OF THE STUDY Plant-herbivore networks are highly specialized in their interactions, yet they are highly variable with regard to the relative importance of specific host species for herbivores. How host species traits determine specialization and species strength in this antagonistic network is still an unanswered question that we addressed in this study. METHODS We assessed plant cover and antiherbivore resistance traits to assess the extent to which they accounted for the variation in specialization and strength of interactions among species in a plant-herbivore network. We studied a tropical antagonistic network including a diverse herbivore-host plant assemblages in different habitat types and climatic seasons, including host plants with different life histories. KEY RESULTS Particular combinations of leaf toughness, trichome density, and phenolic compounds influenced herbivore specialization and host species strength, but with a significant spatiotemporal variation among plant life histories. Conversely, plant-herbivore network parameters were not influenced by plant cover. CONCLUSIONS Our study highlights the importance of species-specific resistance traits of plants to understand the ecological and evolutionary consequences of plant-herbivore interaction networks. The novelty of our research lies in the use of a trait-based approach to understand the variation observed in diverse plant-herbivore networks.

https://bsapubs.onlinelibrary.wiley.com/doi/pdf/10.3732/ajb.1600045

Influence of plant resistance traits in selectiveness and species strength in a tropical plant-herbivore network

Forest succession can influence herbivore communities through changes in host availability, plant quality, microclimate, canopy structure complexity and predator abundance. It is not well known, however, if such influence is constant across years. Caterpillars have been reported to be particularly susceptible to changes in plant community composition across forest succession, as most species are specialists and rely on the presence of their hosts. Nevertheless, in the case of tropical dry forests, plant species have less defined successional boundaries than tropical wet forests, and hence herbivore communities should be able to persist across different successional stages. To test this prediction, caterpillar communities were surveyed during eight consecutive years in a tropical dry forest in four replicated successional stages in Chamela, Jalisco and Mexico. Lepidopteran species richness and diversity were equivalent in mature forests and early successional stages, but a distinctive caterpillar community was found for the recently abandoned pastures. Species composition tended to converge among all four successional stages during the span of eight years. Overall, our results highlight the importance of both primary and secondary forest for the conservation of caterpillar biodiversity at a landscape level. We also highlight the relevance of long‐term studies when assessing the influence of forest succession to account for across year variation in species interactions and climatic factors. Abstract in French is available with online material.

Temporal variation in the influence of forest succession on caterpillar communities: A long‐term study in a tropical dry forest

Plant herbivore interactions can be influenced by abiotic factors such as climate or resource availability. Nevertheless, the influence of climatic variation on the temporal dynamics of plant-herbivore networks has been scarcely studied. In this study we evaluated the influence of temperature and precipitation on the structure and selectiveness of plant-herbivore networks associated to a seasonal tropical ecosystem in the Gulf of Mexico. Although a significant turnover was observed in plant and herbivore species across seasons, high modularity and selectivity of the networks remained relatively constant despite the temporal variation in climatic variables. However, precipitation and temperature was negatively associated with niche overlap for herbivores and positively related to evenness of network interactions. In other words, less stressful conditions are likely to promote the diversification in the use of resources by herbivores, and increase evenness of interactions in the network. An increase in niche overlap and a decrease in the evenness of interactions during the driest and coldest months could be promoted by the presence of less specialized herbivores when availability and quality of host resources is lower. We suggest that the constancy in network selectiveness and modularity facilitates the coexistence of species through the fine distribution of niches and the equitable distribution of food resources in periods of greater precipitation and temperature, when the availability of host plants is greater. Overall, we show for the first time how abiotic factors can influence the emergent structural properties of an antagonistic tropical plant-herbivore network.

Antonio López-Carretero

Papers

Evaluating the Spatio-Temporal Factors that Structure Network Parameters of Plant-Herbivore Interactions

Influence of plant resistance traits in selectiveness and species strength in a tropical plant-herbivore network

Temporal variation in the influence of forest succession on caterpillar communities: A long‐term study in a tropical dry forest

Temporal variation in structural properties of tropical plant-herbivore networks: The role of climatic factors