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1. Several theories have provided a framework for understanding variation in plant defence against herbivores. Among them, the plant apparency theory and the resource availability hypothesis (RAH) have aimed to explain the patterns of defence investment and the selective pressures that have led to the variety of defensive strategies across species. Here we provide a historical review of both theories, present evidence that shaped their development and contrast their predictions. 2. We present the results of a meta-analysis of the utility of the RAH 25 years after it was proposed and compare it to apparency theory. We performed a meta-analysis of 50 studies that have examined plant growth, defences and herbivory in relation to resource availability across latitude and ontogeny. Specifically, we tested four predictions that follow the RAH: (i) species adapted to resource-rich environments have intrinsically faster growth rates than species adapted to resourcepoor environments; (ii) fast-growing species have shorter leaf lifetimes than slow-growing species; (iii) fast-growing species have lower amounts of constitutive defences than slow-growing species; and (iv) fast-growing species support higher herbivory rates than slow-growing species. 3. Our results confirm the predictions that species adapted to resource-poor environments grow inherently more slowly, invest more in constitutive defences and support lower herbivory than species from more productive habitats. Our data also showed that variation in growth rate among species better explains the differences in herbivory than variation in apparency, suggesting that the evolution of different defensive strategies across species is resource, rather than herbivore driven. We also found that the application of this theory appears robust across latitude and ontogeny, as the magnitude of the effect sizes for most of the predictions did not vary significantly between ecosystems or across ontogenic stages. 4. We conclude that the RAH has served as a valid framework for investigating the patterns of plant defences and that its applicability is quite general.

Linking mechanistic processes to the stability of ecological networks is a key frontier in ecology. In trophic networks, “modules”—groups of species that interact more with each other than with other members of the community—confer stability, mitigating effects of species loss or perturbation. Modularity, in turn, is shaped by the interplay between species’ diet breadth traits and environmental influences, which together dictate interaction structure. Despite the importance of network modularity, variation in this emergent property is poorly understood in complex natural systems. Using two years of field data, we quantified interactions between a rich community of lepidopteran herbivores and their host plants across a mosaic of low-resource serpentine and high-resource nonserpentine soils. We used literature and our own observations to categorize herbivore species as generalists (feeding on more than one plant family) or specialists (feeding on one plant family). In both years, the plant-herbivore network was more modular on serpentine than on nonserpentine soils—despite large differences in herbivore assemblage size across years. This structural outcome was primarily driven by reduction in the breadth of host plant use by generalist species, rather than by changes in the composition of species with different fundamental diet breadths. Greater modularity—and thus greater stability—reflects environmental conditions and plastic responses by generalist herbivores to low host plant quality. By considering the dual roles of species traits and ecological processes, we provide a deeper mechanistic understanding of network modularity, and suggest a role for resource availability in shaping network persistence.

Agricultural intensification is a major driver of wild bee decline. Vineyards may be inhabited by plant and animal species, especially when the inter-row space is vegetated with spontaneous vegetation or cover crops. Wild bees depend on floral resources and suitable nesting sites which may be found in vineyard inter-rows or in viticultural landscapes. Inter-row vegetation is managed by mulching, tillage, and/or herbicide application and results in habitat degradation when applied intensively. Here, we hypothesize that lower vegetation management intensities, higher floral resources, and landscape diversity affect wild bee diversity and abundance dependent on their functional traits. We sampled wild bees semi-quantitatively in 63 vineyards representing different vegetation management intensities across Europe in 2016. A proxy for floral resource availability was based on visual flower cover estimations. Management intensity was assessed by vegetation cover (%) twice a year per vineyard. The Shannon Landscape Diversity Index was used as a proxy for landscape diversity within a 750 m radius around each vineyard center point. Wild bee communities were clustered by country. At the country level, between 20 and 64 wild bee species were identified. Increased floral resource availability and extensive vegetation management both affected wild bee diversity and abundance in vineyards strongly positively. Increased landscape diversity had a small positive effect on wild bee diversity but compensated for the negative effect of low floral resource availability by increasing eusocial bee abundance. We conclude that wild bee diversity and abundance in vineyards is efficiently promoted by increasing floral resources and reducing vegetation management frequency. High landscape diversity further compensates for low floral resources in vineyards and increases pollinating insect abundance in viticulture landscapes.

Plant defense against herbivores is multidimensional, and investment into different defense traits is intertwined due to genetic, physiological, and ecological costs. This relationship is expected to generate a trade-off between direct defense and tolerance that is underlain by resource availability, with increasing resources being associated with increased investment in tolerance and decreased investment in direct resistance. We tested these predictions across populations of the shrub Artemisia californica by growing plants sourced from a latitudinal aridity gradient within common gardens located at the southern (xeric) and northern (mesic) portions of its distribution. We measured plant growth rate, resistance via a damage survey, and tolerance to herbivory by experimentally simulating vertebrate herbivory. Plants from more northern (vs. southern) environments were less resistant (received higher percent damage by vertebrate herbivores) and tended to be more tolerant (marginally significant) with respect to change in biomass measured 12 months after simulated vertebrate herbivory. Also, putative growth and defense traits paralleled patterns of resistance and tolerance, such that leaves from northern populations contained lower concentrations of terpenes and increased N, specific leaf area, and % water. Last, plant growth rate did not demonstrate clear clinal patterns, as northern populations (vs. southern populations) grew more slowly in the southern (xeric) garden, but there was no clinal relationship detected in the northern (mesic) garden. Overall, our findings support the prediction of lower resistance and higher tolerance in plant populations adapted to more resource-rich, mesic environments, but this trade-off was not associated with concomitant trade-offs in growth rate. These findings ultimately suggest that plant adaptation to resource availability and herbivory can shape intraspecific variation in multivariate plant defenses.

[Abstract] Aim: Major efforts have been devoted to understanding the geographic pattern of sexual size dimorphism (SSD). Rensch's rule posits that SSD increases with body size in male-biased SSD species and decreases with body size in female-biased SSD species. This pattern, and its inverse, have been mainly explored at the interspecific level, whereas research at the intraspecific level has been largely neglected. Here, we test whether the allometric pattern of SSD in an urodele amphibian conforms to Rensch's rule and evaluate the relative role of four potential mechanisms: sexual selection, fecundity selection, density-dependent resource availability and differential plasticity. Location: Iberian Peninsula. Taxon: Lissotriton boscai (Amphibia: Caudata: Salamandridae). Methods: We used original (field-based) and published data on body size, courtship behaviour and fecundity parameters and a suite of climatic, ecological and genetic (mitochondrial and nuclear markers) predictors to assess these hypotheses. Results: The results showed that SSD increased with increasing female mean body size, supporting the inverse Rensch's rule pattern. Primary productivity-related variables and female density were among the most relevant ecological predictors of SSD after accounting for genetic structure and capture date. Main conclusions: This study reveals that the interplay between the density-dependent resource availability hypothesis and the differential plasticity hypothesis explains the inverse Rensch's rule. We discuss how combining biogeographical and experimental approaches can provide alternative interpretations to the classical sexual and fecundity selection hypotheses on the interpopulation variation in SSD.

Numerous hypotheses have been posited to explain the observed variation in plant defense strategies against herbivory. Under resource-rich environments, plants are predicted to increase their tolerance (limiting resource model; LRM) and, while the resource availability hypothesis (RAH) predicts a decrease in constitutive resistance in plant species growing in resource-rich environments, at the intraspecific level, plants are predicted to follow an opposite pattern (intraspecific RAH). Furthermore, the effect of multiple factors in modulating plant defense strategies has been scarcely explored and is more difficult to predict. Our aim was to understand how plant defense traits respond to herbivory, resource availability and their interactions, and to assess the effects on plant palatability. To this end, we performed an in situ factorial experiment at two sites simulating three herbivory levels and two nutrient availability conditions with the seagrass Posidonia oceanica. Additionally, we performed a series of feeding experiments with its two main herbivores. While plants decreased their constitutive resistance under nutrient fertilization (contrary to intraspecific RAH but in accordance to the RAH), and did not increase allocation to tolerance (likely due to resource limitation, LRM), simulated herbivory induced resistance traits. However, we found no interactive effects of nutrient fertilization and herbivory simulation on plant defense. Both herbivores responded similarly to changes in plant palatability, strongly preferring nutrient-enriched plants and non-clipped plants. This work highlights the need to better understand the drivers of plant defense intraspecific variability in response to resources, particularly in habitat-forming species where changes in plant traits and abundance will cascade onto associated species.

Premise Industrialization and human activities have elevated temperatures and caused novel precipitation patterns, altering soil moisture and nutrient availability. Predicting evolutionary responses to climate change requires information on the agents of selection that drive local adaptation and influence resource acquisition and allocation. Here, we examined the contribution of nutrient and drought stress to local adaptation, and we tested whether trade‐offs across fitness components constrain or facilitate adaptation under resource stress. Methods We exposed 35 families of Boechera stricta (Brassicaceae) to three levels of water and two levels of nutrient supply in a factorial design in the greenhouse. We sourced maternal families from a broad elevational gradient (2499–3530 m a.s.l.), representing disparate soil moisture and nutrient availability. Results Concordant with local adaptation, maternal families from arid, low‐elevation populations had enhanced fecundity under severe drought over those from more mesic, high‐elevation sites. Furthermore, fitness trade‐offs between growth and reproductive success depended on the environmental context. Under high, but not low, nutrient levels, we found a negative phenotypic relationship between the probability of reproduction and growth rate. Similarly, a negative phenotypic association only emerged between fecundity and growth under severe drought stress, not the benign water treatment levels, indicating that stressful resource environments alter the direction of trait correlations. Genetic covariances were broadly concordant with these phenotypic patterns. Conclusions Despite high heritabilities in all fitness components across treatments, trade‐offs between growth and reproduction could constrain adaptation to increasing drought stress and novel nutrient levels.

Resource availability and heterogeneity are recognized as two essential environmental aspects to determine species diversity and community abundance. However, how soil resource availability and heterogeneity determine species diversity and community abundance in highly heterogeneous and most fragile karst landscapes is largely unknown. We examined the effects of soil resource availability and heterogeneity on plant community composition and quantified their relative contribution by variation partitioning. Then, a structural equation model (SEM) was used to further disentangle the multiple direct and indirect effects of soil resource availability on plant community composition. Species diversity was significantly influenced by the soil resource availability in shrubland and woodland but not by the heterogeneity in woodland. Abundance was significantly affected by both soil resource availability and heterogeneity, whereas variation partitioning results showed that soil resource availability explained the majority of the variance in abundance, and the contribution of soil resource heterogeneity was marginal. These results indicated that soil resource availability plays a more important role in determining karst plant community composition than soil resource heterogeneity. Our SEMs further found that the multiple direct and indirect processes of soil resource availability in determining karst species diversity and abundance were different in different vegetation types. Soil resource availability and heterogeneity both played a certain role in determining karst plant community composition, while the importance of soil resource availability far exceeded soil resource heterogeneity. We propose that steering community restoration and reconstruction should be highly dependent on soil resource availability, and multiple direct and indirect pathways of soil resource availability for structuring karst plant communities need to be taken into account. Both limited resource availability and significant resource heterogeneity are key features of karst landscapes. Our study first considered simultaneously resource availability and heterogeneity in karst regions and then quantified and compared the effects of resource availability and heterogeneity on community abundance and species diversity from the relevance‐theoretic perspective. More importantly, our study has important guiding significance to the vegetation restoration.

This study investigates the disparities in the deployment of photovoltaic (PV) technology for carbon emissions reduction across different nations, highlighting the mismatch between countries with high economic capacity and those where PV installation would maximize global decarbonization benefits. This mismatch is discussed based on three key factors influencing decarbonization via PV technology: per capita gross domestic product; carbon intensity of the energy system; and solar resource availability. Current PV deployment is predominantly concentrated in economically advanced countries, and does not coincide with regions where the environmental and economic impact of such installations would be most significant. Through a series of thought experiments, it is demonstrated how alternative prioritization strategies could significantly reduce global carbon emissions. Argument is put forward for a globally coordinated approach to PV deployment, particularly targeting high-impact sunbelt regions, to enhance the efficacy of decarbonization efforts and promote equitable energy access. The study underscores the need for international policies that support sustainable energy transitions in economically less developed regions through workforce development and assistance with the activation of capital.

Purpose The depletion of abiotic resources needs to be discussed in the light of available geologic stocks. For the evaluation of long-term resource availability under consideration of the resources’ functional relevance, the abiotic resource stock that is ultimately available for human purposes needs to be identified. This paper discusses the determination of geologic resources stocks and outlines an approach for the estimation of the resource stocks ultimately available for human use in the long-term. Based on these numbers, existing characterization factors for the assessment of resource depletion by means of the anthropogenic stock extended abiotic depletion potential (AADP) model can be updated. Methods For the assessment of long-term resource availability, the share of abiotic resources ultimately available for human extraction needs to be inferred from the quantity of the elements available in the earth’s crust. Based on existing data on crustal concentrations and assumptions regarding the maximal extractable amount of resource, three different approaches for the determination of ultimately extractable reserves are proposed. The different resource numbers are compared, and their effects on the resulting characterization factors derived from the abiotic depletion potential (ADP) and the AADP models are analyzed. Results and discussion A best estimate for the determination of ultimately extractable reserves is proposed. Based on this new resource number, AADP characterization factors for 35 materials are calculated. The use of ultimately extractable reserves leads to an improved applicability of the AADP model and increases the overall significance of the results. Conclusions Resource security is a premise for sustainable development. The use of resources needs to be evaluated in the context of their decreasing availability for future generations. Thus, resource choices should also be based on an analysis of available resource stocks. The proposed AADP characterization factors based on ultimately extractable reserves will enable a more realistic evaluation of long-term resource availability for human purposes.