Browsing by Person "Esler, Karen J."

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Bird and insect pollinators differ in specialization and potential pollination services along disturbance and resource gradients
(2023) Neu, Alexander; Cooksley, Huw; Esler, Karen J.; Pauw, Anton; Roets, Francois; Schurr, Frank M.; Schleuning, Matthias
Combined studies of the communities and interaction networks of bird and insect pollinators are rare, especially along environmental gradients. Here, we determined how disturbance by fire and variation in sugar resources shape pollinator communities and interactions between plants and their pollinating insects and birds. We recorded insect and bird visits to 21 Protea species across 21 study sites and for 2 years in Fynbos ecosystems in the Western Cape, South Africa. We recorded morphological traits of all pollinator species (41 insect and nine bird species). For each site, we obtained estimates of the time since the last fire (range: 2–25 calendar years) and the Protea nectar sugar amount per hectare (range: 74–62 000 g/ha). We tested how post‐fire age and sugar amount influence the total interaction frequency, species richness and functional diversity of pollinator communities, as well as pollinator specialization (the effective number of plant partners) and potential pollination services (pollination service index) of insects and birds. We found little variation in the total interaction frequency, species richness and functional diversity of insect and bird pollinator communities, but insect species richness increased with post‐fire age. Pollinator specialization and potential pollination services of insects and birds varied differently along the environmental gradients. Bird pollinators visited fewer Protea species at sites with high sugar amount, while there was no such trend for insects. Potential pollination services of insect pollinators to Protea species decreased with increasing post‐fire age and resource amounts, whereas potential pollination services of birds remained constant along the environmental gradients. Despite little changes in pollinator communities, our analyses reveal that insect and bird pollinators differ in their specialization on Protea species and show distinct responses to disturbance and resource gradients. Our comparative study of bird and insect pollinators demonstrates that birds may be able to provide more stable pollination services than insects.
Functional traits shape plant–plant interactions and recruitment in a hotspot of woody plant diversity
(2023) Cooksley, Huw; Dreyling, Lukas; Esler, Karen J.; Griebenow, Stian; Neumann, Günter; Valentine, Alex; Schleuning, Matthias; Schurr, Frank M.
Understanding and predicting recruitment in species‐rich plant communities requires identifying functional determinants of both density‐independent performance and interactions. In a common‐garden field experiment with 25 species of the woody plant genus Protea, we varied the initial spatial and taxonomic arrangement of seedlings and followed their survival and growth during recruitment. Neighbourhood models quantified how six key functional traits affect density‐independent performance, interaction effects and responses. Trait‐based neighbourhood models accurately predicted individual survival and growth from the initial spatial and functional composition of species‐rich experimental communities. Functional variation among species caused substantial variation in density‐independent survival and growth that was not correlated with interaction effects and responses. Interactions were spatially restricted but had important, predominantly competitive, effects on recruitment. Traits increasing the acquisition of limiting resources (water for survival and soil P for growth) mediated trade‐offs between interaction effects and responses. Moreover, resprouting species had higher survival but reduced growth, likely reinforcing the survival–growth trade‐off in adult plants. Resource acquisition of juvenile plants shapes Protea community dynamics with acquisitive species with strong competitive effects suffering more from competition. Together with functional determinants of density‐independent performance, this makes recruitment remarkably predictable, which is critical for efficient restoration and near‐term ecological forecasts of species‐rich communities.
Interactions between protea plants and their animal mutualists and antagonists are structured more by energetic than morphological trait matching
(2022) Neu, Alexander; Cooksley, Huw; Esler, Karen J.; Pauw, Anton; Roets, Francois; Schurr, Frank M.; Schleuning, Matthias
Traits mediate mutualistic and antagonistic interactions between plants and animals, and should thus be useful for predicting trophic species interactions. Studies to date have examined the importance of morphological trait matching for plant–animal interactions, but have rarely explored the extent to which these interactions are shaped by matching between energetic provisions of plants and energetic demands of animals. We tested whether energetic and/or morphological trait matching shapes interactions between Protea plant species and their interacting animal mutualists and antagonists in the Cape Floristic Region, South Africa. We recorded interactions between 22 Protea species, pollinating insects and vertebrates as well as seed predators (endophagous insect larvae in protea cones) at 21 study sites. To relate species interactions to matching trait pairs, we measured key morphological traits (shape and size of flower heads and seed cones, and mouth part length as well as body length) and quantified the animals' energetic demands (metabolic rate) together with the plants' energetic provisions (nectar sugar amount, seed‐to‐cone mass ratio). We calculated log ratios of both energetic and morphological traits between animals and plants as predictor variables for the number of observed interactions between Protea species and their animal interaction partners. For both mutualistic and antagonistic interactions, we found significant effects of morphological and energetic trait ratios on the interactions between plants and animals. Trait ratios accounted for 11% to 22% of variation in species interactions. Consistent with energetic trait matching, we found a hump‐shaped relationship between interaction frequency and log ratios of energetic traits of animals and plants, indicating that interactions were most frequent at intermediate log ratios between energetic demand and provision. Effects of morphological trait ratios on interactions were statistically supported in most cases, but were variable in the magnitude and shape of the predicted relationships. Across animal taxa and interaction types, energetic traits had more consistent effects on interactions between plants and animals than morphological traits. This suggests that energy can function as an important interaction currency and facilitate the understanding and prediction of trophic species interactions.