Abstract:
In North American deserts, many species of cactus attract ants to their extrafloral nectaries; the ants actively defend the food source, and hence the plant, against herbivores. In thermally extreme environments, however, networks of positive and negative interactions like these are likely to be sensitive to the thermal limitations of each of the interacting species. We compared the thermal tolerance of a common phytophagous cactus bug, Narnia pallidicornis (Hemiptera: Coreidae), to that of the ants that defend the cactus Ferocactus wislizeni in the Sonoran Desert, USA. We used flow-through respirometry to experimentally determine the thermal limit of the herbivore and compared this to the thermal limits of the ant defenders, determined previously. In the field, we recorded herbivore frequency (proportion of plants with N. pallidicornis) and abundance (the number of N. pallidicornis per plant) in relation to ambient temperature, ant species presence and identity, and fruit production. We show that N. pallidicornis has a higher thermal tolerance than the four most common ant mutualists, and in the laboratory can survive very high temperatures, up to 43°C. Herbivore frequency and abundance in the field were not related to the daily high temperatures observed. Plants that were not defended by ants were occupied by more N. pallidicornis, although they showed no reduction in fruit set. Therefore, herbivory is likely to continue on fishhook barrel cacti even at high temperatures, especially those temperatures beyond the thermal tolerance of the ant defenders. The consequences of increased herbivory, however, remain unclear. Mutualisms are essential for ecosystem functioning; it is important to understand the thermal sensitivity of these interactions, especially in light of expected increases in global temperature regimes.
Abstract:
Pollinators feed on patchily distributed plants, forcing them to decide when to move between patches and when to switch plant species. The "plant-pollinator landscape' is shaped by an interacting set of plant and pollinator attributes: flowering phenology sets the distance that pollinators need to travel between patches of a given species to obtain sufficient food, while the pollinators' search capacities and dietary specificity determines the likelihood that they can and will make that journey. These sets of traits do not vary independently, allowing us to identify several characteristic landscapes and the types of organisms that occupy them. This chapter describes five such landscapes, attempting in each case to determine whether phenological variation within plant species helps to explain the ability of pollinators to persist. The first two landscapes are occupied by highly specialized pollinators and (respectively) synchronously flowering and asynchronously flowering plants. Intraspecific phenological variation is likely to have critical consequences for pollinator persistence in these two landscapes. The third and fourth landscapes are occupied by relatively generalized pollinators and (respectively) synchronously flowering and asynchronously flowering plants. The former is probably the most common landscape, encompassing most temperate plant-pollinator interactions. Pollinators in these landscapes are less likely to be strongly influenced by phenological variation in any one of their resource plants, due to their ability to switch foods easily while remaining local. The fifth landscape is occupied by generalist pollinators that may migrate. Little is known about resource use of individual migrants, but it is possible that at least some of them rely on geographical gradients in flowering time of certain preferred species. -from Author
PMID: 23704115;PMCID: PMC3662527;Abstract:
BackgroundPlants in over one hundred families in habitats worldwide bear extrafloral nectaries (EFNs). EFNs display a remarkable diversity of evolutionary origins, as well as diverse morphology and location on the plant. They secrete extrafloral nectar, a carbohydrate-rich food that attracts ants and other arthropods, many of which protect the plant in return. By fostering ecologically important protective mutualisms, EFNs play a significant role in structuring both plant and animal communities. And yet researchers are only now beginning to appreciate their importance and the range of ecological, evolutionary and morphological diversity that EFNs exhibit.ScopeThis Highlight features a series of papers that illustrate some of the newest directions in the study of EFNs. Here, we introduce this set of papers by providing an overview of current understanding and new insights on EFN diversity, ecology and evolution. We highlight major gaps in our current knowledge, and outline future research directions. Conclusions Our understanding of the roles EFNs play in plant biology is being revolutionized with the use of new tools from developmental biology and genomics, new modes of analysis allowing hypothesis-testing in large-scale phylogenetic frameworks, and new levels of inquiry extending to community-scale interaction networks. But many central questions remain unanswered; indeed, many have not yet been asked. Thus, the EFN puzzle remains an intriguing challenge for the future. © 2013 The Author. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved.
Abstract:
Mutualisms often involve significant costs for participants. Costs are inflicted by mutualists themselves, as well as by associated, non-mutualistic species. These costs are rarely quantified, however, particularly the ones extrinsic to the pairwise interaction. We compare costs inflicted by an obligate mutualist pollinator and two common exploiters of an Arizona yucca over a 2-year period. The magnitude of seed damage from seed and fruit-feeding beetle larvae (Carpophilus longus, Nitidulidae) was similar to damage from the seed-eating larvae of Yucca schottii's pollinator moth Tegeticula yuccasella (Prodoxidae), averaging about 15 seeds destroyed per fruit in each case. The two seed predators usually fed within the same fruits, although rarely side by side. In contrast, the presence of fruit-galling moth larvae (Prodoxus y-inversus, Prodoxidae) appeared to benefit the yucca: individual Tegeticula destroyed only half as many seeds in galled fruits as they did in ungalled fruits. We discuss three general implications of these results. Firstly, the costs of non-mutualists to the two mutualistic partners are not necessarily parallel. Secondly, measurable costs of non-mutualists do not necessarily translate into an impact on the success of the mutualism itself, because they may be incurred after mutualistic activities take place. Finally, the costs of mutualists to each other can differ substantially depending on the presence or absence of non-mutualistic species.
