Host selection by ovipositing cowpea weevils: patterning of input from separate sense organs

Ablations were performed to identify the sense organs used in host selection by ovipositing cowpea weevils, Callosobruchus maculatus. Antennae, foretarsi and palpi (maxillary + labial) were removed singly or in combination, and females were offered pairwise choices of four host species. Removal of the palpi consistently had the greatest effect on host choice, whereas the relative importance of other organs depended on the pair of hosts tested. Different organs may provide conflicting input as to the preferred host; certain ablations led to a complete reversal in preference (as opposed to a simple loss of discrimination). Input from separate organs appeared to be received in a dominance hierarchy.

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Sélection de l'hôte lors de la ponte de Callosobruchus maculatus: modélisation des influx provenant séparément des divers organes sensoriels

Résumé Les ablations ont servi d'étape initiale lors de la détermination des organes sensoriels impliqués dans la sélection du lieu de ponte par C. maculatus. Les antennes, les tarses antérieurs, les palpes (maxillaires et labiaux) ont été retirés seuls ou en combinaison. Les femelles ont eu des choix binaires entre les graines de 4 légumineuses: Cicer arietinum, Glycine max, Phaseolus vulgaris, Vigna unguiculata. Chaque combinaison d'ablations était accompagnée d'un témoin chez lequel les mêmes ablations étaient unilatérales. C'est l'ablation des palpes qui a le plus modifié le choix de l'hôte; l'influence relative des autres organes dépendait des paires d'hôtes offerts. Différents organes peuvent fournir des influx opposés quant à l'hôte préféré certaines ablations ont conduit à une inversion complète des préférences. Il semble que les influx sensoriels formaient une gamma avec hiérarchie dominante. Dans les choix binaires, les préférences initiales des femelles intactes ont été supprimées avec l'ablation des palpes seuls, cependant elles n'avaient pas été modifiées par l'ablation conjointe des palpes et des tarses. Dans ces expériences, l'influx antennaire ne devenait dominant qu'après ablation des deux autres organes sensoriels. Les préférences des femelles avec ablations unilatérales ne différaient pas de celles des femelles intactes.

     

Conservation biology: predicting birds' responses to forest fragmentation

Understanding species' ecological responses to habitat fragmentation is critical for biodiversity conservation, especially in tropical forests. A detailed recent study has shown that changes in the abundances of bird species following fragmentation may be dramatic and unpredictable.     

Complex selection on life-history traits and the maintenance of variation in exaggerated rostrum length in acorn weevils

Trophic interactions can trigger the development of exaggerated specialized characters and promote morphological diversification. For example, acorn weevils (genus Curculio) present strikingly long rostrums, which are used by females to perforate oviposition holes through the seed coat. Species exhibiting longer rostrums are known to exploit larger acorns, and therefore rostrum length is thought to be subject to selection to match the preferred acorn type. However, rostrum length is strongly correlated with body size, and morphological divergence could result from either selection on rostrum length for optimal food exploitation or from other pressures acting on body size. We collected infested acorns at oak forests where the large Curculio elephas and the small-bodied Curculio glandium co-occur. There were no interspecific differences in adult female body size to rostrum length allometric relationships, and rostrum length is equally correlated with body size in either species. MtDNA-based species identification showed that C. glandium larvae were present within acorns of all sizes, whereas C. elephas larvae were restricted to acorns above a minimum size, irrespective of oak species. Hence, exploitation of large acorns can hardly have triggered rostrum enlargement, as the small sized C. glandium adults (with short rostrums) could perforate and oviposit in both small and large acorns. Rather, increased rostrum length is probably a by-product of the larger body sizes of individuals emerging from bigger acorns, which allow increased larval size and enhance larval survival likelihood. Summarizing, when exaggerated feeding traits co-vary with other body features, interspecific morphological variability may result from contrasting selective pressures acting on these correlated characters.     

Small sample bias in dynamic occupancy models

Occupancy models may be used to estimate the probability that a randomly selected site in an area of interest is occupied by a species (ψ), given imperfect detection (p). This method can be extended, given multiple survey periods, to permit the estimation of seasonal probabilities of ψ, colonization (γ), persistence (φ), and extinction (1 − φ) in season t. We evaluated the sampling properties of estimators of these parameters using simulated data across a range of the parameters, differing levels of sites and visits, with a published dynamic occupancy model (Royle and Kery 2007). Bias depended largely on p and the number of visits, but also on the number of sites, ψ_t, γ, and 1 − φ. To decrease bias in all parameters to near zero, our results suggest that the number of required visits will depend on p, such that the probability of detection at an occupied site is near 0.9, and the required number of sites will be near 60 for ψ_t estimation and 120 or greater for γ and 1 − φ estimation. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.     

Assemblage-level responses of Neotropical bats to forest loss and fragmentation

Habitat loss and fragmentation are the most important causes of biological diversity loss, changing the properties of the remaining environment. The Neotropical Region is one of the most affected areas due to the conversion of natural habitats into agricultural activities and deforestation. In this region, bats represent almost 50% of all mammal species, reaching the highest taxonomic and functional diversity. Bats are valuable indicators of biodiversity and ecosystem health, but their response to habitat loss and fragmentation was poorly studied in Argentina. The aim of this study was to analyze the response of bat assemblages to habitat alteration in Northwestern Argentina. The specimens were collected in eight different localities, four well-preserved and four disturbed sites of the Yungas Forests. To describe the structure of bat assemblages, rank-abundance curves, species richness and Shannon (H’) and Simpson (D’) diversity indexes were calculated. To test the assemblage variations among sites, PCA and NPMANOVA analysis were performed. After 96 sampling nights, a total of 565 bats from 23 species were captured. A great variation in the assemblage structure was registered, regardless the disturbance level of the sites. These variations were not significantly different according to statistical analysis. The results support the hypothesis that areas with moderate fragmentation can sustain a high diversity of bat species. Moreover, these results showed that consistent responses to landscape composition at the assemblage level are harder to identify in fragmented Neotropical Forests. The responses of bats to habitat alteration tend to be highly species-specific.     

Avian responses to forest fragmentation during the breeding and non-breeding seasons

Forest fragmentation represents a threat to several bird species worldwide. Several factors can change across seasons (e.g. bird perception of the landscape, weather conditions, biotic interactions), which can modify the response of bird populations to forest fragmentation. However, most studies have been conducted only during the breeding season. Here we assessed the relationship between forest fragmentation (patch area and patch isolation) with population abundances of resident species during both the breeding and the non-breeding seasons. Bird population abundances (all species in the community, subsets of forest and habitat generalist species and for individual species) were estimated across a gradient of area-isolation in a semi-arid forest in Cordoba, Argentina. Population abundance of the overall avian community and of the subset of forest species declined with patch area reduction independently of the season. By contrast, the subset of habitat generalist species was not affected by patch area reduction or by the increase in patch isolation, either during the breeding or during the non-breeding season. When the analyses were carried out for individual species, we found four forest species and one habitat generalist species whose responses (the relationship between population abundance and patch area or with isolation) were different between breeding and non-breeding seasons. The negative effects of forest fragmentation were found mainly during the breeding season. Our results suggest that reduction of patch area may lead to a reduction of more than 65% of the population abundance of forest bird species, during both the breeding and the non-breeding season. Therefore, there is an urgent need to conserve large forest patches within the region as irreplaceable elements for the conservation of populations of several species.     

Season‐modulated responses of Neotropical bats to forest fragmentation

Seasonality causes fluctuations in resource availability, affecting the presence and abundance of animal species. The impacts of these oscillations on wildlife populations can be exacerbated by habitat fragmentation. We assessed differences in bat species abundance between the wet and dry season in a fragmented landscape in the Central Amazon characterized by primary forest fragments embedded in a secondary forest matrix. We also evaluated whether the relative importance of local vegetation structure versus landscape characteristics (composition and configuration) in shaping bat abundance patterns varied between seasons. Our working hypotheses were that abundance responses are species as well as season specific, and that in the wet season, local vegetation structure is a stronger determinant of bat abundance than landscape‐scale attributes. Generalized linear mixed‐effects models in combination with hierarchical partitioning revealed that relationships between species abundances and local vegetation structure and landscape characteristics were both season specific and scale dependent. Overall, landscape characteristics were more important than local vegetation characteristics, suggesting that landscape structure is likely to play an even more important role in landscapes with higher fragment‐matrix contrast. Responses varied between frugivores and animalivores. In the dry season, frugivores responded more to compositional metrics, whereas during the wet season, local and configurational metrics were more important. Animalivores showed similar patterns in both seasons, responding to the same group of metrics in both seasons. Differences in responses likely reflect seasonal differences in the phenology of flowering and fruiting between primary and secondary forests, which affected the foraging behavior and habitat use of bats. Management actions should encompass multiscale approaches to account for the idiosyncratic responses of species to seasonal variation in resource abundance and consequently to local and landscape scale attributes.     

Evaluating the responses of forest ecosystems to climate change and CO2 using dynamic global vegetation models

The climate has important influences on the distribution and structure of forest ecosystems, which may lead to vital feedback to climate change. However, much of the existing work focuses on the changes in carbon fluxes or water cycles due to climate change and/or atmospheric CO₂, and few studies have considered how and to what extent climate change and CO₂ influence the ecosystem structure (e.g., fractional coverage change) and the changes in the responses of ecosystems with different characteristics. In this work, two dynamic global vegetation models (DGVMs): IAP‐DGVM coupled with CLM3 and CLM4‐CNDV, were used to investigate the response of the forest ecosystem structure to changes in climate (temperature and precipitation) and CO₂ concentration. In the temperature sensitivity tests, warming reduced the global area‐averaged ecosystem gross primary production in the two models, which decreased global forest area. Furthermore, the changes in tree fractional coverage (ΔF_tree; %) from the two models were sensitive to the regional temperature and ecosystem structure, i.e., the mean annual temperature (MAT; °C) largely determined whether ΔF_tree was positive or negative, while the tree fractional coverage (F_tree; %) played a decisive role in the amplitude of ΔF_tree around the globe, and the dependence was more remarkable in IAP‐DGVM. In cases with precipitation change, F_tree had a uniformly positive relationship with precipitation, especially in the transition zones of forests (30% < F_tree < 60%) for IAP‐DGVM and in semiarid and arid regions for CLM4‐CNDV. Moreover, ΔF_tree had a stronger dependence on F_tree than on the mean annual precipitation (MAP; mm/year). It was also demonstrated that both models captured the fertilization effects of the CO₂ concentration.     

Combining information from range use and habitat selection: sex-specific spatial responses to habitat fragmentation in tawny owls Strix aluco

How individuals respond to habitat heterogeneity is usually measured as variation in range size and by ranking the relative importance of habitat types (habitat selection). The combined effect of how individuals incorporate different habitat types in their home ranges and allocate their time budget between them is rarely derived. Additionally, when home range size varies between individuals, habitat selection analyses might be flawed if foraging decisions are based on variation in absolute rather than proportional availability. We investigated the suitability of standard analytical approaches by measuring the spatial responses of tawny owls to habitat fragmentation. These owls inhabited woodland of various sizes, representing a fragmentation gradient from open farmland with small, isolated woodland patches, to continuous woodland within their home ranges. In 17 territories within open farmland, the available area covered by woodland increased with the square root of the area of open land embraced in the home range. The owls did not display functional response in habitat selection, but females selected woodland more strongly than males. Females utilised woodland 10 times more intensively in farmland than in continuous woods, whereas males utilised farmland woods 3.2 times more intensively. Moreover, females in farmland exploited woodland 3.2 times as intensively as males, apparently because of higher travel costs in open areas. Since the extensive variation in intensity of use as a function of total availability was not indicated from the analysis of habitat selection, we suggest that information about intensity of use be more widely used as a supplementary measure of habitat use patterns than appears to be the practice at present.     

Host plant recognition in monophagous weevils: specificity in feeding responses of Ceutorhynchus constrictus and the variable effect of sinigrin

Host plant relations of the monophagous weevil Ceutorhynchus constrictus Marsh. (Coleoptera: Curculionidae: Ceutorhynchinae) feeding on garlic mustard, Alliaria petiolata (Bieb.) Cavara & Grande (Cruciferae) were studied in the laboratory. Most other crucifers were rejected in choice tests using garlic mustard as a reference plant, but Brassica nigra, Sinapis alba and Thlaspi arvense were as acceptable as the host plant. Flowering plants of Descurainia sophia were acceptable while young plants of this species were not. The most important feeding stimulants in extracts of garlic mustard were uncharged, water soluble compounds. The most abundant glucosinolate in garlic mustard, sinigrin, was a feeding stimulant, too. However, the feeding stimulatory activity of sinigrin was only expressed in the presence of still unidentified uncharged compounds from garlic mustard leaves. Host plant relations in monophagous crucifer-feeding insects is discussed in relation to the distinctness of glucosinolate patterns found in their host plants.

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Zusammenfassung Ceutorhynchus constrictus Marsh. (Coleoptera: Chrysomelidae: Ceutorhynchinae) ist ein monophager Rüsselkäfer, der an Knoblauchhederich frisst. Das Wirtswahl-Verhalten dieses Käfers ist im Labor untersucht worden. Die meisten Crucifiren waren im Wahlversuche nicht akzeptiert, wenn Knoblauchhederich als Vergleichspflanze vorhanden war. Von Brassica nigra, Sinapis alba, und Thlaspi arvense wurden im Vergleich gleiche Mengen verzehrt wie von der Wirtspflanze. Blühende Descurainia sophia Pflanzen wurden, im Gegensatz zu Jungpflanzen der gleichen Art, angenommen. Die wichtichsten Phagostimulanten in Extrakten von Knoblauchhederich-Blättern waren ungeladene, wasserlösliche Substanzen. Das häufigste Glukosinolat im Knoblauchhederich, Sinigrin, war auch ein Phagostimulant. Doch war die phagostimulierende Wirkung von Sinigrin nur in Kombinationen mit noch nicht identifizierten, ungeladenen Substanzen aus Knoblauchhederich-Blätter nachweisbar. Wirtspfanzen-Beziehungen von monophagen Insekten werden diskutiert im Zusammenhang mit der Eigenart des Glukosinolat-Inhaltes ihrer Wirtspflanzen.

     

Spatial metrics effect of forest fragmentation on forest bird abundance and site occupancy probability: the influence of patch size and isolation

The persistence of species taxa within fragmented habitats is dependent on the source–sink metapopulation processes, and forest patch size and isolation are key factors. Unveiling species–patch area and/or species–patch isolation relationships may help provide crucial information for species and landscape management. In this study, relationship between forest patch size and isolation with abundance and occupancy probability of forest-dependent birds was investigated. This study was based within a coastal landscape that faces deleterious human activities such as clearing for agriculture. The study aimed to answer the question of whether the size and extent of isolation of forest patches influence abundance and/or occupancy probability of forest-specialist and generalist birds. Two bird species, namely Tiny Greenbul Phyllastrephus debilis subsp. rabai and Yellow-bellied Greenbul Chlorocichla flaviventris, were used as models. Birds were surveyed using distance sampling methods, and spatial metrics were measured from satellite imagery. Focal forest size and distance between forest patches were the most influential metrics whereby abundance and occupancy probabilities increased with increasing patch size, but were negatively influenced by increasing gaps between patches. These findings provide evidence of the existence of patch size/ isolation–occupancy relationships characterised by higher occupancy rate of large patches and distance-dependent dispersal, which decreased with increasing gaps between patches. Controlling deleterious human activities that reduce forest size should be a priority for the long-term conservation of forest-dependent birds.     

Feeding group responses of a Neotropical termite assemblage to rain forest fragmentation

Biomass collapse and its associated microclimatic stresses within recently isolated rain forest fragments may negatively affect species diversity of most resident taxa. However, for some decomposer organisms, increased resource availability via accompanying tree die-off may effect positive responses, at least for a time, with implications for rates of nutrient cycling and greenhouse gas release. This study investigates the early effects of forest fragmentation on a Neotropical termite assemblage. Numbers of encounters (surrogate for relative abundance) and species richness of wood and leaf-litter feeders, soil feeders, and the whole assemblage, were studied across true forest islands and mainland sites at a hydroelectric reservoir in French Guiana. Results showed no overall effect of fragmentation on either total termite encounters or species richness. However, numbers of encounters and species richness of wood and leaf-litter feeders showed positive responses to forest fragmentation. By contrast, soil feeders showed a negative response for numbers of encounters and no significant effect for species richness. Environmental data suggest that increased tree die-off, and other edge effects associated with biomass collapse, were underway at the time of sampling. Resulting increase in resource availability may therefore explain the positive influence on wood and leaf-litter feeders. A possible decrease in predation pressure from ants with decrease in island size was not tested for, but was a likely effect of the flooded matrix habitat. Fragmentation effects on soil feeder encounters may be due to the energetic and microclimatic constraints of feeding lower down the humification gradient of termite food substrates, but were not sufficient to affect species richness. The patterns revealed suggest that rates of wood decomposition following tree die-off, and of soil nutrient cycling, under different rain forest fragmentation scenarios, merit further study.     

Inferring wildlife poaching in southeast Asia with multispecies dynamic occupancy models

Determining the ‘space race’ between co-occurring species is crucial to understand the effects of interspecific interactions on the extinction risk of species threatened by poachers and predators. Dynamic two-species occupancy models provide a flexible framework to decompose complex species interaction patterns, while accounting for imperfect detection. These models can describe poachers–wildlife interactions, as they allow estimating occupancy, extinction and colonisation probabilities of wildlife conditional on the occurrence of poachers and vice versa. We applied our model to a case study on wildlife poaching in the eastern plains of Cambodia. We used co-occurrence data extracted from the database of the SMART partnership to study the distribution dynamics between poachers and six ungulate species pooled together into the tiger prey guild. We used four years of survey data reporting the locations of snares and of presence signs of the ungulates recorded by rangers during their monthly multi-patrolling sessions. Our results showed that a substantial proportion of the sites occupied by ungulate species went extinct over the years of the study while the proportion of sites colonised by poachers increased. We also showed, for the first time, that spatio-temporal heterogeneity in the patrolling effort explains a great deal of the variation in the detection of poachers and ungulates. Our approach provides practitioners with a flexible and robust tool to assess conservation status of species and extinction risk of wildlife populations. It can assist managers in better evaluating, learning and adapting the patrolling strategies of rangers.     

Ecological traits modulate bird species responses to forest fragmentation in an Amazonian anthropogenic archipelago

Aim

We assessed patterns of avian species loss and the role of morpho‐ecological traits in explaining species vulnerability to forest fragmentation in an anthropogenic island system. We also contrasted observed and detectability‐corrected estimates of island occupancy, which are often used to infer species vulnerability.

Location

Tucuruí Hydroelectric Reservoir, eastern Brazilian Amazonia.

Methods

We surveyed forest birds within 36 islands (3.4–2,551.5 ha) after 22 years of post‐isolation history. We applied species–area relationships to assess differential patterns of species loss among three data sets: all species, forest specialists and habitat generalists. After controlling for phylogenetic non‐independence, we used observed and detectability‐corrected estimates of island occupancy separately to build competing models as a function of species traits. The magnitude of the difference between these estimates of island occupancy was contrasted against species detectability.

Results

The rate of species loss as a function of island area reduction was higher for forest specialists than for habitat generalists. Accounting for the area effect, forest fragmentation did not affect the overall number of species regardless of the data set. Only the interactive model including natural abundance, habitat breadth and geographic range size was strongly supported for both estimates of island occupancy. For 30 species with detection probabilities below 30%, detectability‐corrected estimates were at least tenfold higher than those observed. Conversely, differences between estimates were negligible or non‐existent for all 31 species with detection probabilities exceeding 45.5%.

Main conclusions

Predicted decay of avian species richness induced by forest loss is affected by the degree of habitat specialisation of the species under consideration, and may be unrelated to forest fragmentation per se. Natural abundance was the main predictor of species island occupancy, although habitat breadth and geographic range size also played a role. We caution against using occupancy models for low‐detectability species, because overestimates of island occupancy reduce the power of species‐level predictions of vulnerability.

     

Assemblage-level responses of phyllostomid bats to tropical forest fragmentation: land-bridge islands as a model system

Aim Working within a system of high structural contrast between fragments and the surrounding matrix, we assessed patterns of species loss and changes in species composition of phyllostomid bats on artificial land‐bridge islands relative to mainland assemblages, and evaluated the responses of bats to forest edges. We further examined the relative influence of local‐scale characteristics (e.g. vegetation structure, island area) versus landscape attributes (e.g. forest cover, patch density) and the importance of spatial scale in determining phyllostomid species richness and composition on islands. Location Islands in Gatún Lake and adjacent mainland peninsulas in the Barro Colorado Nature Monument, Panama. Methods Bats were sampled over a 2‐year period on 11 islands as well as at forest‐edge and interior sites on adjacent mainland, resulting in > 8400 captures. Results The islands harboured a less diverse and structurally simplified phyllostomid bat fauna. Islands far from the mainland were especially species‐poor. This decline in species richness was associated with compositional shifts towards assemblages strongly dominated by frugivores with good dispersal abilities. Members of other ensembles, most importantly gleaning animalivores, were much less common or absent. Although overall species composition was not significantly altered, species richness at continuous forest‐edge sites was significantly lower compared with that at interior sites. Distance from the mainland and amount of forest cover in the landscape were the best predictors of species richness and assemblage composition. Responses were scale‐dependent. At the local scale, species richness was independent of island area but was correlated positively with distance from the mainland. In contrast, area effects became more important at larger spatial scales, suggesting that many species use multiple fragments. Main conclusions Our results underline the conservation value of small habitat remnants, which, even when embedded in a hostile matrix, can support a relatively diverse bat fauna, provided that there is a low degree of patch isolation and spatial proximity to larger tracts of continuous forest. Although the results at the assemblage level were inconclusive, we demonstrate that certain bat species and ensembles, particularly gleaning animalivores, exhibit high edge‐sensitivity. Our results point to habitat loss rather than changes in landscape configuration as the main process after isolation underlying phyllostomid bat responses, suggesting that conservation efforts should focus on habitat preservation instead of trying to minimize fragmentation per se at the expense of habitat amount.     

The phylogeny of acorn weevils (genus Curculio) from mitochondrial and nuclear DNA sequences: the problem of incomplete data

We considered the contribution of two mitochondrial and two nuclear data sets for the phylogenetic reconstruction of 22 species of seed beetles in the genus Curculio (Coleoptera: Cuculionidae). A phylogenetic tree from representatives found on various hosts was inferred from a combined data set of mitochondrial DNA cytochrome oxidase subunit I, mitochondrial cytochrome b, nuclear elongation factor 1alpha, and nuclear phosphoglycerate mutase, used for the first time as a molecular marker. Separate parsimony analyses of each data set showed that individual gene trees were mainly congruent and often complementary in the support of clades but the analysis was complicated by failure of PCR amplification of nuclear genes for many taxa and hence missing data entries. When the four gene partitions were combined in a simultaneous analysis despite the missing data, this increased the resolution and taxonomic coverage compared to the individual source trees. Alternative approaches of combining the information via supertree methodology produced a comparatively less resolved tree, and hence seem inferior to combining data matrices even in cases where numerous taxa are missing. The molecular data suggest a classification of the European species into two species groups that are in accordance with morphological characteristics but the data do no support any of the previously recognised American species groups.