Resilience in Plant-Herbivore Networks during Secondary Succession

<div><p>Extensive land-use change in the tropics has produced a mosaic of successional forests within an agricultural and cattle-pasture matrix. Post-disturbance biodiversity assessments have found that regeneration speed depends upon propagule availability and the intensity and duration of disturbance. However, reestablishment of species interactions is still poorly understood and this limits our understanding of the anthropogenic impacts upon ecosystem resilience. This is the first investigation that evaluates plant-herbivore interaction networks during secondary succession. In particular we investigated succession in a Mexican tropical dry forest using data of caterpillar associations with plants during 2007–2010. Plant-herbivore networks showed high resilience. We found no differences in most network descriptors between secondary and mature forest and only recently abandoned fields were found to be different. No significant nestedness or modularity network structure was found. Plant-herbivore network properties appear to quickly reestablish after perturbation, despite differences in species richness and composition. This study provides some valuable guidelines for the implement of restoration efforts that can enhance ecological processes such as the interaction between plants and their herbivores.</p> </div

Network measurements in four successional stages (Mean ± SD) of the tropical dry forest in the Chamela region.

<p>Network measurements in four successional stages (Mean ± SD) of the tropical dry forest in the Chamela region.</p

Plant-herbivore networks in different successional stages.

<p>Each network represents all the interactions observed in all the sampling times and in all replicates of the same successional stage. Species bar size represents the number of interactions it has. <b>Plants are represented in green</b>: 1) <i>Acacia farnesiana</i>, 2) <i>Acacia macracantha</i>, 3) <i>Lonchocarpus</i> sp. L, 4) <i>Apoplanesia paniculata</i>, 5) <i>Ayenia micrantha</i>, 6) <i>Coccoloba liebmannii</i>, 7) <i>Caesalpinia caladenia</i>, 8) <i>Casearia nitida</i>, 9) <i>Colubrina triflora</i>, 10) <i>Coursetia caribaea</i>, 11) <i>Croton pseudoniveus</i>, 12) <i>Dalbergia congestiflora</i>, 13) <i>Guapira macrocarpa</i>, 14) <i>Gyrocarpus jatrophifolius</i>, 15) <i>Heliocarpus pallidus</i>, 16) <i>Hintonia latiflora</i>, 17) <i>Justicia candicans</i>, 18) <i>Leucaena lanceolata</i>, 19) <i>Lonchocarpus</i> sp. 2, 20) <i>Lonchocarpus eriocarinalis</i>, 21) <i>Lonchocarpus</i> sp. F, 22) <i>Lonchocarpus</i> sp. A, 23) <i>Lonchocarpus</i> sp. K, 24) <i>Mimosa arenosa</i>, 25) <i>Mimosa pigra</i>, 26) <i>Phyllanthus mocinianus</i>, 27) <i>Piptadenia constricta</i>, 28) <i>Rauvolfia tetraphylla</i>, 29) <i>Spondias purpurea</i>, 30) <i>Stemmadenia donnell-smithii</i>, 31) <i>Thouinia paucidentata</i>, 32) <i>Trichilia trifolia</i>. <b>Lepidopterans are represented in blue</b>: 1) <i>Agraulis vanillae incarnate, 2) Anomis editrix, 3)Apatelodes pudefacta, 4) Automeris io, 5)Dasylophia eminens, 6) Eutelia auratrix, 7) Geometridae sp. 10, 8) Geometridae sp. 12, 9) Geometridae sp. 7, 10) Geometridae sp. 9, 11) Gonodonta pyrgo, 12) Norape tenera, 13) Orgya sp., 14) Polygonus manueli manueli, 15) Syllepsis hortalis, 16) Wockia chewbacca, 17) Arctiidae sp. 1, 18) O114, 19)O14, 20) O18, 21)O190, 22 Geometridae sp. 34, 23)O3, 24)O32, 25) Geometridae sp. 59, 26)O67, 27)O80</i>.</p

Significant <i>a posteriori</i> contrasts.

<p>Significant <i>a posteriori</i> contrasts.</p

What makes a good pollinator? : Abundant and specialised insects with long flight periods transport the most strawberry pollen

Despite the importance of insect pollination to produce marketable fruits, insect pollination management is limited by insufficient knowledge about key crop pollinator species. This lack of knowledge is due in part to (1) the extensive labour involved in collecting direct observations of pollen transport, (2) the variability of insect assemblages over space and time and (3) the possibility that pollinators may need access to wild plants as well as crop floral resources.We address these problems using strawberry in the United Kingdom as a case study. First, we compare two proxies for estimating pollinator importance: flower visits and pollen transport. Pollen-transport data might provide a closer approximation of pollination service, but visitation data are less time-consuming to collect. Second, we identify insect parameters that are associated with high importance as pollinators, estimated using each of the proxies above. Third, we estimated insects' use of wild plants as well as the strawberry crop.Overall, pollinator importances estimated based on easier-to-collect visitation data were strongly correlated with importances estimated based on pollen loads. Both frameworks suggest that bees (Apis and Bombus) and hoverflies (Eristalis) are likely to be key pollinators of strawberries, although visitation data underestimate the importance of bees.Moving beyond species identities, abundant, relatively specialised insects with long active periods are likely to provide more pollination services.Most insects visiting strawberry plants also carried pollen from wild plants, suggesting that pollinators need diverse floral resources.Identifying essential pollinators or pollinator parameters based on visitation data will reach the same general conclusions as those using pollen transport data, at least in monoculture crop systems. Managers may be able to enhance pollination service by preserving habitats surrounding crop fields to complement pollinators' diets and provide habitats for diverse life stages of wild pollinators.Peer reviewe

Fertilization using manure minimizes the trade-offs between biodiversity and forage production in agri-environment scheme grasslands

A common practice used to restore and maintain biodiversity in grasslands is to stop or decrease the use of fertilizers as they are a major cause of biodiversity loss. This practice is problematic for farmers who need fertilizers to increase forage and meet the nutritional needs of livestock. Evidence is needed that helps identify optimal fertilizer regimes that could benefit biodiversity and livestock production simultaneously over the long-term. Here, we evaluated the impact of different fertilizer regimes on indicators related to both biodiversity (plant, pollinator, leaf miners and parasitoid Shannon-Weiner diversity, bumblebee abundance, nectar productivity and forb species richness), and forage production (ash, crude protein, ruminant metabolizable energy and dry matter). To this end, we used data from a grassland restoration experiment managed under four nutrient inputs schemes for 27 years: farmyard manure (FYM; 72 kg N ha-1 yr-1), artificial nitrogen-phosphorus and potassium (NPK; 25 kg N ha-1 yr-1), FYM + NPK (97 kg N ha-1 yr-1) and no-fertilizer. Results showed strong trade-offs between biodiversity and forage production under all treatments even in applications lower than the critical load in the EU. Overall, farmyard manure was the fertilizer that optimized production and biodiversity while 97 kg N ha-1 yr-1 of fertilizer addition (FYM+NPK) had the most negative impact on biodiversity. Finally, forage from places where no fertilizer has been added for 27 years did not meet the nutritional requirements of cattle, but it did for sheep. Rethinking typical approaches of nutrient addition could lead to land management solutions suitable for biological conservation and agriculture

Differential effects of fertilisers on pollination and parasitoid interaction networks

1. Grassland fertilisation drives non‐random plant loss resulting in areas dominated by perennial grass species. How these changes cascade through linked trophic levels, however, is not well understood. 2. We studied how grassland fertilisation propagates change through the plant assemblage into the plant–flower‐visitor, plant–leaf miner and leaf miner–parasitoid networks using a year's data collection from a long‐term grassland fertiliser application experiment. Our experiment had three fertiliser treatments each applied to replicate plots 15 m2 in size: mineral fertiliser, farmyard manure, and mineral fertiliser and farmyard manure combined, along with a control of no fertiliser. 3. The combined treatment had the most significant impact, and both plant species richness and floral abundance decreased with the addition of fertiliser. While insect species richness was unaffected by fertiliser treatment, fertilised plots had a significantly higher abundance of leaf miners and parasitoids and a significantly lower abundance of bumblebees. The plant–flower‐visitor and plant–herbivore networks showed higher values of vulnerability and lower modularity with fertiliser addition, while leaf miner–parasitoid networks showed a rise in generality. 4. The different groups of insects were impacted by fertilisers to varying degrees: while the effect on abundance was the highest for leaf miners, the vulnerability and modularity of flower‐visitor networks was the most affected. The impact on the abundance of leaf miners was positive and three times higher than the impact on parasitoids, and the impact on bumblebee abundance was negative and double the magnitude of impact on flower abundance. 5. Overall, our results show that while insect species richness was unaffected by fertilisers, network structure changed significantly as the replacement of forbs by grasses resulted in changes in relative abundance across trophic levels, with the direction of change depending on the type of network. 6. Synthesis. By studying multiple networks simultaneously, we were able to rank the relative impact of habitat change on the different groups of species within the community. This provided a more holistic picture of the impact of agricultural intensification and provides useful information when deciding on priorities for mitigation