Attracting pollinators vs escaping herbivores: eco-evolutionary dynamics of plants confronted with an ecological trade-off

A large number of plant traits are subject to an ecological trade-off between attracting pollinators and escaping herbivores. The interplay of both plant-animal interactions determines their evolution. Within a plant-pollinator-herbivore community in which interaction strengths depend on trait-matching, eco-evolutionary dynamics are studied using the framework of adaptive dynamics. We characterize the type of selection acting on the plant phenotype and the consequences for multispecies coexistence. We find that pollination favors stabilizing selection and coexistence. In contrast, herbivory fosters runaway selection, which threatens plant-animal coexistence. These contrasting dynamics highlight the key role of ecological trade-offs in structuring ecological communities. In particular, we show that disruptive selection is possible when such trade-offs are strong. While the interplay of pollination and herbivory is known to maintain plant polymorphism in several cases, our work suggests that it might also have fueled the diversification process itself.

Stable isotope paleoecology of the Baynunah Formation

The Baynunah Formation contains the only known late Miocene terrestrial fossils from the Arabian Peninsula. Based on renewed field work since 2002, we present paleoenvironmental and dietary reconstructions from carbon isotope data from plant wax biomarkers and carbon and oxygen isotope data from fossil tooth enamel in combination with previously published fossil tooth enamel and pedogenic carbonate isotope data. The organic and isotopic data indicate that the highly seasonal ecosystem supported a herbivore community that relied heavily on C4 vegetation. Carbon isotope and molecular abundance data from n-alkanes indicate mostly mixed C3-C4 and C4-dominated ecosystems. Carbon isotope data from fossil teeth indicate a range of C3, mixed C3-C4, and C4 diets, with suids, deinotherids, and rhinocerotids browsing, and bovids, elephantids, and equids mixed feeding to grazing. Hippopotamids show the most positive carbon and most negative oxygen values, with narrow ranges indicating year-round grazing and semi- aquatic habits. The Baynunah sivatheres represent the earliest evidence for a C4-dominanted diet among giraffids. Equid intratooth oxygen isotope profiles indicate a highly seasonal hydroclimate regime, reflecting strong monsoonal conditions with a single rainy season. Corresponding carbon profiles record large seasonal changes in equid diets, with mainly grazing in the wet season and increased browsing in the dry season. Baynunah ecosystems comprised savanna habitats (woody grasslands) with the proboscidean trackway site of Mleisa 1 likely being a seasonally flooded C4 grassland.

Animal body size distribution influences the ratios of nutrients supplied to plants

Nutrients released through herbivore feces have the potential to influence plant-available nutrients and affect primary productivity. However, herbivore species use nutrients in set stoichiometric ratios that vary with body size. Such differences in the ratios at which nutrients are used leads to differences in the ratios at which nutrients are deposited through feces. Thus, local environmental factors that affect the average body size of an herbivore community (such as predation risk and food availability) influence the ratios at which fecal nutrients are supplied to plants. Here, we assess the relationship between herbivore body size and the nitrogen-to-phosphorus ratios of herbivore feces. We examine how shifts in the average body size of an herbivore community alter the ratios at which nitrogen and phosphorus are supplied to plants and test whether such differences in the stoichiometry of nutrient supply propagate through plants. We show that dung from larger-bodied herbivores contain lower quantities of phosphorus per unit mass and were higher in N:P ratio. We demonstrate that spatial heterogeneity in visibility (a proxy for predation risk and/or food availability) and rainfall (a proxy for food availability), did not affect the overall amount of feces deposited but led to changes in the average body size of the defecating community. Feces deposited in areas of higher rainfall and reduced visibility originated from larger herbivores and were higher in N:P ratios. This indicates that processes that change the size distribution of herbivore communities, such as predation or size-biased extinction, have the potential to alter the nutrient landscape for plants.

The ecological consequences of herbivore-induced plant responses on plant–pollinator interactions

Plant induced responses to herbivory have long been found to function as plant direct and indirect defenses and to be major drivers of herbivore community and population dynamics. While induced defenses are generally understood as cost-saving strategies that allow plants to allocate valuable resources into defense expression, it recently became clear that, in particular, induced metabolic changes can come with significant ecological costs. In particular, interactions with mutualist pollinators can be significantly compromised by herbivore-induced changes in floral morphology and metabolism. We review recent findings on the evidence for ecological conflict between defending against herbivores and attracting pollinators while using similar modes of information transfer (e.g. visual, olfactory, tactile). Specifically, we discuss plant traits and mechanisms through which plants mediate interactions between antagonists and mutualist and present functional hypotheses for how plants can overcome the resulting conflicts.

Changes in arthropod community but not plant quality benefit a specialist herbivore on plant under reduced water availability

Plants grow under reduced water availability can have divergent effects on insect herbivores, in some instances producing benefits to them. However, the forces mediating these positive impacts remain mostly unclear. We conducted a manipulative field study using a specialist herbivore Pieris rapae, and its host plant, Rorippa indica, in two populations to identify how water availability impacts overall plant quality and multitrophic interactions. We observed that R. indica growing under low water availability led to higher survival of P. rapae larvae. The increase in survival of eggs and larvae was related to the reduced abundance of other herbivores and natural enemies. Water availability had differential impacts on members of the herbivore community through changes in plant quality. Low water availability decreased the quality of R. indica to most herbivores as indicated by reduced abundance in the field and decreased relative growth rate in feeding assays. In contrast, the performance of P. rapae larvae were not affected by differences in sympatric R. indica grown under different water availability. These results indicate that local P. rapae possess some physiological adaptation to overcome fluctuations in host quality. Our findings illustrate that reduced water availability is beneficial to a specialist herbivore, but detrimental to most other herbivores. Our work highlights the complex roles of the arthropod communities associated with plants in determining the impacts of water availability on insect herbivores.

Evidence of plant– arthropod interaction in the fossil assemblage from Pitsidia (Messara Basin, Crete, Greece; Upper Miocene)

As major components of natural ecosystems, plants interact with the biotic and abiotic environment developing a spectrum of different responses at various biological levels. Such biotic interactions are detectible in the plant fossil record and provide an outline of ecological functions during the past. The recently described Late Miocene plant assemblage from Pitsidia in the Messara Basin was examined for arthropod mediated damage. Most of the damage was detected on abundant, more than 2.500 specimens, well-preserved material of Myrica lignitum foliage, providing a broad range of traces. Eighteen different types of leaf modifications were distinguished, with hole, margin, surface feeding, lamina distortion and possibly galls as the most common while mining and exophytic oviposition were rare. Among this damage, it appears that only a few represent host-specialist feeding. These findings could serve as a database for the component herbivore community on M. lignitum. Considerations of this insect damage regarding past habitats and vegetation at Pitsidia as well as on plant–arthropod co-association are discussed. Several forms of arthropod damage on other plant taxa in this assemblage are briefly mentioned.