Diel fragrance pattern correlates with olfactory preferences of diurnal and nocturnal flower visitors in Salix caprea (Salicaceae)

Floral scent, often a complex mixture of several volatile organic compounds (VOCs), has generally been interpreted as an adaptation to attract pollinators. However, not many studies have analysed which VOCs are functionally relevant for the reproductive success of a plant. Here, we show that, in Salix caprea (Salicaceae), temporal changes in floral scent emission during the day and night attract two different types of flower visitor: bees during the day and moths during the evening and night. We analysed the contribution of the two flower visitor groups to the reproductive success of the plant. The differences in scent emitted during the peak activity times of flower visitors (day versus night) were quantified and the response of 13 diurnal/nocturnal pollinator taxa to the floral scents was tested using gas chromatographic and electroantennographic techniques. Many of the c. 40 identified scent compounds were physiologically active, and bees and moths responded to nearly identical sets of compounds, although the response strengths differed. In bioassays, bees preferred the most abundant 1,4‐dimethoxybenzene over lilac aldehyde, a compound with increased emission at night, whereas moths preferred lilac aldehyde over 1,4‐dimethoxybenzene. Pollination by wind plus nocturnal pollinators (mainly moths) or by wind alone contributed less to seed set than pollination by wind plus diurnal pollinators (mainly bees). This suggests that the emission of scent during the night and attracting moths have no significant effect on reproductive success. It is possible that the emission of lilac aldehydes and other compounds at night is s result of phylogenetic constraints. Future studies should investigate whether moths may produce a marginal fitness gain in some years and/or some populations. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 175 , 624–640.     

Mercury contamination and stable isotopes reveal variability in foraging ecology of generalist California gulls

Environmental contaminants are a concern for animal health, but contaminant exposure can also be used as a tracer of foraging ecology. In particular, mercury (Hg) concentrations are highly variable among aquatic and terrestrial food webs as a result of habitat- and site-specific biogeochemical processes that produce the bioaccumulative form, methylmercury (MeHg). We used stable isotopes and total Hg (THg) concentrations of a generalist consumer, the California gull (Larus californicus), to examine foraging ecology and illustrate the utility of using Hg contamination as an ecological tracer under certain conditions. We identified four main foraging clusters of gulls during pre-breeding and breeding, using a traditional approach based on light stable isotopes. The foraging cluster with the highest δ¹⁵N and δ³⁴S values in gulls (cluster 4) had mean blood THg concentrations 614% (pre-breeding) and 250% (breeding) higher than gulls with the lowest isotope values (cluster 1). Using a traditional approach of stable-isotope mixing models, we showed that breeding birds with a higher proportion of garbage in their diet (cluster 2: 63–82% garbage) corresponded to lower THg concentrations and lower δ¹⁵N and δ³⁴S values. In contrast, gull clusters with higher THg concentrations, which were more enriched in ¹⁵N and ³⁴S isotopes, consumed a higher proportion of more natural, estuarine prey. δ³⁴S values, which change markedly across the terrestrial to marine habitat gradient, were positively correlated with blood THg concentrations in gulls. The linkage we observed between stable isotopes and THg concentrations suggests that Hg contamination can be used as an additional tool for understanding animal foraging across coastal habitat gradients.     

Phylogenetic and phenotypic structure among Banksia communities in south‐western Australia

Aim Phylogenetic and phenotypic patterns among coexisting banksias (Banksia, Proteaceae) in the infertile, fire‐prone landscapes of south‐western Australia were examined for evidence of community structuring. It was expected that closely related species would be spatially clustered (underdispersed) as a consequence of widespread recent speciation, strong edaphic fidelity and low dispersability. We also expected that edaphic filtering would result in phenotypic clustering of traits related to habitat specialization and that competitive exclusion among closely related species with similar regeneration biology and growth form would result in phenotypic overdispersion of these latter traits. Location Southwest Australian Floristic Region (SWAFR). Methods Based on published data for coexistence (richness and frequency) of Banksia species at 40 sites in the three floristic provinces, phylogenetic, soil type and morphological mean pairwise distance and mean nearest taxon distance were calculated for each site and compared with null communities. Patterns of co‐occurrence were examined at the local and subregional (provincial) scales. Results Of the 40 sites assessed, 21–30 displayed phylogenetic clustering of Banksia species (5–11 significantly) such that, overall, co‐occurring taxa were more closely related than expected by chance. Banksias in the Transitional Rainfall and Southeast Coastal Provinces were more likely to display phylogenetic clustering than in the High Rainfall Province. A significant trend for phylogenetic clustering associated with edaphic specialization (27–30 sites) was observed, as well as a significant trend for phenotypic overdispersion associated with growth form (25–28 sites). Results for regeneration biology depended on the metric used. Main conclusions We demonstrate spatial clustering of closely related banksias at the local and provincial scales, consistent with their restricted distribution (recent widespread speciation, patchy habitat availability and limited dispersability) in this geologically old and stable region. The clustering of closely related species may also be a consequence of habitat filtering linked to edaphic fidelity in the SWAFR flora, while overdispersion in growth form suggests that functional divergence favours coexistence in Banksia communities.     

Host plant toxins and unpalatability of Neacoryphus bicrucis (Hemiptera: Lygaeidae)

Abstract. 1. Host plant choice of the seed bug, Neacoryphus bicrucis Say (Hemiritera, Lygaeidae), was evaluated in four different Georgia habitats. N. bicrucis utilized only species of Senecio as host plants at a granite outcrop and at old fields on the coastal plain, in the piedmont, and in the Blue Ridge Mountains.
2. In laboratory tests N. bicrucis is distasteful to the green anole lizard, Anolis carolinensis Voight. Only six of ninety field-collected bugs were eaten in palatability trials while eighty-four of the remaining ninety attacked bugs were rejected by lizards without apparent harm. However, the bugs were palatable to Fowler's toads, Bufo woodhousei fowleri Hinckley, which ate all thirty-six bugs offered to them.
3. N. bicrucis selectively sequesters pyrrolizidine alkaloids from Senecio spp. These may cause the insects' distastefulness to green anoles. In palatability trials, lizards ate all twenty insects reared on sunflower seeds, Helianthus annus, but rejected all twenty reared on Senecio smallii.     

Metabolic adaptations for isopod specialization in three species of Dysdera spiders from the Canary Islands

The spider genus Dysdera is considered to comprise specialist isopod feeders, although the degree of specialization varies between species, depending on morphological (shape of chelicerae), behavioural (attack tactics) and metabolic (food quality of prey) adaptations. Dysdera has radiated extensively in the Canary Islands (currently 47 endemic species are described) and codistributed species have different cheliceral shapes and body sizes indicating different feeding niches. In the present study, we investigate the existence of metabolic adaptations to feeding on isopods by three endemic species (Dysdera insulana Simon, Dysdera macra Simon and Dysdera verneaui Simon) from Tenerife. We hypothesize that there is enhanced extraction efficiency of fundamental macronutrients from isopods compared with control prey in species with special morphological and behavioural adaptations for this prey type. We measure quantitatively spider growth, dry mass consumption, lipid and nitrogen consumption, and calculate growth efficiency and efficiency of utilization of dry mass, lipid and nitrogen. The results show that all three species are able to utilize both prey types, indicating that none of them are strict isopod specialist. Dysdera insulana shows enhanced growth efficiency and D. macra shows enhanced nitrogen extraction efficiency compared with D. verneaui when feeding on Porcellio rather than on Musca. Both traits indicate likely adaptations for the utilization of isopods. Spider species, sex and prey type all affect lipid and nitrogen extraction efficiencies, indicating that spiders do not simply extract nutrients in the proportions available. The results support the hypothesis that adaptations for enhanced digestion of focal prey evolve in species that already have adaptations for enhanced capture success.     

Spatial scale of aggregation in three acarine predator species with different degrees of polyphagy

Aggregative responses by the predatory mites, Phytoseiulus persimilis, Typhlodromus occidentalis, and Amblyseius andersoni (Acari: Phytoseiidae), to spatial variation in the density of mobile stages of Tetranychus urticae (Acari: Tetranychidae) were studied over different spatial scales on greenhouse roses. Significant spatial variations in prey numbers per leaflet, per leaf, per branch or per plant were present in all experimental plots. None of the predator species responded to prey numbers per plant, and all searched randomly among plants. Within a plant, the oligophagous P. persimilis searched randomly among branches, but aggregated strongly among leaves within a branch and among leaflets within a leaf. The narrowly polyphagous T. occidentalis searched randomly among leaflets within a leaf and amond leaves within a branch, but aggregated strongly among leaflets or leaves within a plant. The boradly polyphagous A. andersoni searched randomly among leaflets within a leaf, a branch or a plant, and among leaves within a branch or a plant, but distributed themselves more often on branches with lower prey densities. Thus, specialist predators aggregate strongly at lower spatial levels but show random search at higher spatial levels, whereas generalist predators show random search at lower spatial levels but aggregate at higher spatial levels. This is the first empirical evidence demonstrating the relation between the degree of polyphagy and the spatial scale of aggregation. It is also concluded that both the prey patch size (i.e. grain) and predator foraging range (i.e. extent) are important for analyzing spatial scales of predator aggregation. The importance of studying spatial scale of aggregation is also discussed in relation to predator-prey metapopulation dynamics.     

How intraspecific variation in seed‐dispersing animals matters for plants

Seed dispersal by animals is a complex phenomenon, characterized by multiple mechanisms and variable outcomes. Most researchers approach this complexity by analysing context‐dependency in seed dispersal and investigating extrinsic factors that might influence interactions between plants and seed dispersers. Intrinsic traits of seed dispersers provide an alternative way of making sense of the enormous variation in seed fates. I review causes of intraspecific variability in frugivorous and granivorous animals, discuss their effects on seed dispersal, and outline likely consequences for plant populations and communities. Sources of individual variation in seed‐dispersing animals include sexual dimorphism, changes associated with growth and ageing, individual specialization, and animal personalities. Sexual dimorphism of seed‐dispersing animals influences seed fate through diverse mechanisms that range from effects caused by sex‐specific differences in body size, to influences of male versus female cognitive functions. These differences affect the type of seed treatment (e.g. dispersal versus predation), the number of dispersed seeds, distance of seed dispersal, and likelihood that seeds are left in favourable sites for seeds or seedlings. The best‐documented consequences of individual differences associated with growth and ageing involve quantity of dispersed seeds and the quality of seed treatment in the mouth and gut. Individual specialization on different resources affects the number of dispersed plant species, and therefore the connectivity and architecture of seed‐dispersal networks. Animal personalities might play an important role in shaping interactions between plants and dispersers of their seeds, yet their potential in this regard remains overlooked. In general, intraspecific variation in seed‐dispersing animals often influences plants through effects of these individual differences on the movement ecology of the dispersers. Two conditions are necessary for individual variation to exert a strong influence on seed dispersal. First, the individual differences in traits should translate into differences in crucial characteristics of seed dispersal. Second, individual variation is more likely to be important when the proportions of particular types of individuals fluctuate strongly in a population or vary across space; when proportions are static, it is less likely that intraspecific differences will be responsible for changes in the dynamics and outcomes of plant–animal interactions. In conclusion, focusing on variation among foraging animals rather than on species averages might bring new, mechanistic insights to the phenomenon of seed dispersal. While this shift in perspective is unlikely to replace the traditional approach (based on the assumption that all important variation occurs among species), it provides a complementary alternative to decipher the enormous variation observed in animal‐mediated seed dispersal.     

Dietary specialization and climatic‐linked variations in extant populations of Ethiopian wolves

Understanding of the biology of rarity is central to the conservation of some endangered species. Rare taxa are often reported to be specialized, but they are usually poorly studied. The Ethiopian wolf (Canis simensis) is endemic to the Ethiopian highlands and in two major populations, Bale and Arsi in the southern range of the species, it preys almost exclusively upon diurnal rodents all year round, mainly molerats Tachyoryctes macrocephalus and common molerats T. splendens, respectively. Where these large rodents are absent or rare, wolves are expected to rely more heavily on nocturnal rats or livestock. Prey remains in 161 scats from five newly studied populations confirmed that wolves are indeed specialist rodent hunters elsewhere, and that their narrow diets are dominated by diurnal Murinae rats (60–83% of prey occurrences). Swamp rats Otomys typus were the main prey, followed by grass rats Arvicanthis abyssinicus. Common molerats, Lophuromys rats and nocturnal Stenocephalemys spp. constituted the variable portion of the diets, and their proportional contributions varied across populations in relation to elevation and latitude. Towards the north, where the climate is drier and human populations more dense, wolves predate more frequently on rat‐sized prey, including nocturnal species, with implications for the survival of small populations in the Northern Highlands.