Costs and benefits for partners in mutualistic interactions can vary greatly, but surprisingly little is known about the factors that drive this variation across systems. We conducted a meta-analysis of ant-plant protective mutualisms to quantify the effects of ant defenders on plant reproductive output, to evaluate if reproductive effects were predicted from reductions in herbivory and to identify characteristics of the plants, ants and environment that explained variation in ant protection. We also compared our approach with two other recent meta-analyses on ant-plant mutualisms, emphasizing differences in our methodology (using a weighted linear mixed effects model) and our focus on plant reproduction rather than herbivore damage. Based on 59 ant and plant species pairs, ant presence increased plant reproductive output by 49% and reduced herbivory by 62%. The effects on herbivory and reproduction within systems were positively correlated, but the slope of this relationship (0.75) indicated that tolerance to foliar herbivory may be a common plant response to absence of ant guards. Furthermore, the relationship between foliar damage and reproduction varied substantially among systems, suggesting that herbivore damage is not a reliable surrogate for fitness consequences of ant protection. Studies that experimentally excluded ants reported a smaller effect of ant protection on plant reproduction than studies that relied upon natural variation in ant presence, suggesting that study methods can affect results in these systems. Of the ecological variables included in our analysis, only plant life history (i.e., annual or perennial) explained variation in the protective benefit of mutualistic ants: presence of ants benefitted reproduction of perennials significantly more than that of annuals. These results contrast with other quantitative reviews of these relationships that did not include plant life history as an explanatory factor and raise several questions to guide future research on ant-plant protection mutualisms.

Abstract:Habitat fragmentation is considered a leading cause of plant extinction, and matrix models provide a powerful set of tools with which to identifying mechanisms that influence population declines. We surveyed the ecological literature to determine what components of plant demography have been studied in fragmented habitats, and determined the elasticity values of the vital rates influenced by these components. We found that there is a major disparity between the ecological processes and stages of life history with large demographic impacts and the focus of empirical research on plants in fragmented habitats. While the growth and survivorship of large, established individuals have the highest elasticity values, the focus of empirical research has been on components of reproduction and seedling dynamics. We argue that elucidating the demographic mechanisms underlying population declines in fragmented habitats, and developing strategies for mitigating these declines, will be challenging without a greater focus on understanding how fragmentation alters adult plant growth and survivorship.

We assessed the exposure and acute toxicity of naled, applied aerially as an ultra-low-volume spray for mosquito control, on late instar larvae of the Miami blue (Cyclargus thomasi bethunebakeri) (Comstock and Huntington 1943) (Lepidoptera: Lycaenidae), an imperiled South Florida butterfly. We concurrently evaluated the control efficacy against caged adult female salt-marsh mosquitoes (Aedes taeniorhynchus) (Wiedemann 1821) (Diptera: Culicidae). This 3-yr study was conducted in north Key Largo (Monroe County, FL) beginning in 2006. The field trials incorporated 15 sampling stations: nine in the target spray zone, three in the spray drift zone at varying distances from the target zone, and three in the control zone not subjected to naled spray drift. A total of six field spray trials were completed, three at an altitude of 30.5 m (100 feet), and three at 45.7 m (150 feet). For all trials, the ultra-low-volume application of Trumpet EC insecticide (78% naled) at a rate of 54.8 ml/ha (0.75 fl. oz/acre) was effective in killing caged adult mosquitoes in the target zone. Butterfly larvae survival was significantly reduced in the spray zone compared with drift and control zones. Analysis of insecticide residue data revealed that the mortality of the late instar butterfly larvae was a result of exposure to excess residues of naled. Additional research is needed to determine mitigation strategies that can limit exposure of sensitive butterflies to naled while maintaining mosquito control efficacy.

Summary1 Variation in antiherbivore defences among individuals within a plant species may be influenced by intrinsic characteristics of the plant, environmental conditions and the interactions between these factors. 2 We used a long-term field experiment and a laboratory palatability trial to elucidate the effects of plant age, nutrient availability and ant occupancy on herbivore damage sustained by Cordia alliodora, a common neotropical myrmecophyte. 3 Herbivory in this system was influenced by both plant characteristics and environmental conditions, and the relative importance of these variables changed with plant age. 4 Five-year-old plants had a higher frequency of ant occupation and more workers per domatium than 1-year-old plants. 5 Plant age did not significantly affect herbivory in either field studies or laboratory palatability trials conducted with a specialist herbivore. In the field, however, 1-year-old plants tended to have higher levels of herbivory than 5-year-old plants. 6 There was a trend towards lower herbivory in trees that had been fertilized. Additionally, leaves from fertilized trees were significantly less palatable to specialist herbivores. 7 In 1-year-old plants, the abundance of ants in domatia had no effect on herbivory of nearby leaves. In contrast, ant abundance and herbivory were negatively correlated for 5-year-old trees, demonstrating that ants provide effective defence only for older plants. 8 These results suggest that understanding ant-plant-herbivore relationships requires examining how biotic and abiotic factors and their interactions change with plant ontogeny. Although our work focused on one particular ant-plant system, the importance of ontogenetic variation in antiherbivore defence is increasingly recognized as a critical area of study in plant defence theory.

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We examined avian communities of kopjes (naturally occurring insular rock outcrops) in grassland and thorn tree woodland habitats in the Seronera region of Serengeti National Park, northwestern Tanzania. Although kopjes cover a small proportion of the Park's area, they provide resources that are uncommon in the Serengeti landscape and are known to host diverse, yet poorly documented, biotic communities. The primary objectives of this study were (1) to compare avian communities of kopjes with those of their surrounding habitat matrixes; (2) to compare the avian communities among kopjes; and (3) to determine the effects of kopje characteristics (e.g., size, vegetation cover, level of human disturbance and matrix type) on avian diversity and community composition. The avian communities of kopjes differed significantly from those of the matrixes in species composition and guild characteristics. Rare species, frugivorous species and nectarivorous species were more abundant on kopjes, whereas there were more ground-feeding species in matrix sites. Species richness was positively correlated with the area of kopjes covered by tall vegetation (5+ m), but neither total habitat area nor total vegetation cover significantly affected avian diversity. The surrounding habitat type, the fruiting phenology of Ficus and Commiphora trees and the level of human disturbance also influenced the presence and abundance of individual species and accounted for differences in community composition among kopjes. Our results show that kopjes support unique avian assemblages comprising many species that are otherwise rare in Serengeti, and consequently that kopjes may be local hotspots of avian diversity in the region.

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