Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Underrepresentation of dietary‐specialist larval Lepidoptera in small forest fragments: Testing alternative mechanisms
Title: Underrepresentation of dietary‐specialist larval Lepidoptera in small forest fragments: Testing alternative mechanisms
Abstract Growing evidence suggests that organisms with narrow niche requirements are particularly disadvantaged in small habitat patches, typical of fragmented landscapes. However, the mechanisms behind this relationship remain unclear. Dietary specialists may be particularly constrained by the availability of their food resources as habitat area shrinks. For herbivorous insects, host plants may be filtered out of small habitat fragments by neutral sampling processes and deterministic plant community shifts due to altered microclimates, edge effects and browsing by ungulates.We examined the relationship between forest fragment area and the abundance of dietary‐specialist and dietary‐generalist larval Lepidoptera (caterpillars) and their host plants in the northeastern USA. We surveyed caterpillars and their host plants over 3 years in equal‐sized plots within 32 forest fragments varying in area between 3 and 1014 ha. We tested whether the abundances and species richness of dietary specialists increased more than those of dietary generalists with increasing fragment area and, if so, whether the difference could be explained by reduced host plant availability or increased browsing by white‐tailed deer (Odocoileus virginianus).The overall abundance of dietary specialists was positively related to fragment area; the relationship was substantially weaker for dietary generalists. There was notable variation among species within diet breadth groups, however. There was no effect of fragment area on the diversity of dietary‐specialist or dietary‐generalist caterpillars. Deer activity was not related to the abundances of either dietary‐generalist or dietary‐specialist caterpillars.Plant community composition was strongly associated with fragment area. Larger fragments were more likely to include host plants for both dietary‐specialist and dietary‐generalist caterpillars. Deer activity was correlated with decreased host plant availability for both groups, with a slightly stronger impact on host plants of dietary specialists. Although dietary specialists were more likely to lack host plants in fragments, the relationship between fragment area and host availability did not depend on caterpillar diet breadth.This study provides further evidence that decreasing patch area disproportionately impacts specialist consumers. Because this relationship was derived from equal‐sized plots, it is robust to some criticisms levelled at fragmentation research. The mechanisms for specialist consumer declines, however, remain elusive.  more » « less
Award ID(s):
1557086
PAR ID:
10585042
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ; ; ; ;
Publisher / Repository:
Journal of Animal Ecology
Date Published:
Journal Name:
Journal of Animal Ecology
Volume:
94
Issue:
4
ISSN:
0021-8790
Page Range / eLocation ID:
786 to 799
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; (, Oecologia)
    Reduced ecological specialization is an emerging, general pattern of ecological networks in fragmented landscapes. In plant–herbivore interactions, reductions in dietary specialization of herbivore communities are consistently associated with fragmented landscapes, but the causes remain poorly understood. We propose several hypothetical bottom–up and top–down mechanisms that may reduce the specificity of plant–herbivore interactions. These include empirically plausible applications and extensions of theory based on reduced habitat patch size and isolation (considered jointly), and habitat edge effects. Bottom–up effects in small, isolated habitat patches may limit availability of suitable hostplants, a constraint that increases with dietary specialization. Poor hostplant quality due to inbreeding in such fragments may especially disadvantage dietary specialist herbivores even when their hostplants are present. Size and isolation of habitat patches may change patterns of predation of herbivores, but whether such putative changes are associated with herbivore dietary specialization should depend on the mobility, size, and diet breadth of predators. Bottom–up edge effects may favor dietary generalist herbivores, yet top–down edge effects may favor dietary specialists owing to reduced predation. An increasingly supported edge effect is trophic ricochets generated by large grazers/browsers, which remove key hostplant species of specialist herbivores. We present empirical evidence that greater deer browsing in small forest fragments disproportionately reduces specialist abundances in lepidopteran assemblages in northeastern USA. Despite indirect evidence for these mechanisms, they have received scant direct testing with experimental approaches at a landscape scale. Identifying their relative contribu 
    more » « less
  2. ; ; ; ; ; (, Oecologia)
    Abstract An animal’s diet breadth is a central aspect of its life history, yet the factors determining why some species have narrow dietary breadths (specialists) and others have broad dietary breadths (generalists) remain poorly understood. This challenge is pronounced in herbivorous insects due to incomplete host plant data across many taxa and regions. Here, we develop and validate machine learning models to predict pollen diet breadth in bees, using a bee phylogeny and occurrence data for 682 bee species native to the United States, aiming to better understand key drivers. We found that pollen specialist bees made an average of 72.9% of their visits to host plants and could be predicted with high accuracy (mean 94%). Our models predicted generalist bee species, which made up a minority of the species in our dataset, with lower accuracy (mean 70%). The models tested on spatially and phylogenetically blocked data revealed that the most informative predictors of diet breadth are plant phylogenetic diversity, bee species’ geographic range, and regional abundance. Our findings also confirm that range size is predictive of diet breadth and that both male and female specialist bees mostly visit their host plants. Overall, our results suggest we can use visitation data to predict specialist bee species in regions and for taxonomic groups where diet breadth is unknown, though predicting generalists may be more challenging. These methods can thus enhance our understanding of plant-pollinator interactions, leading to improved conservation outcomes and a better understanding of the pollination services bees provide. 
    more » « less
  3. ; ; (, G3: Genes, Genomes, Genetics)
    Whitehead, A (Ed.)
    Abstract Bees are palynivorous insects that vary widely in the number of plant families from which they collect pollen. Their evolutionary history has been marked by multiple transitions in diet breadth between specialists that only visit specific plant genera (narrow diet breadth) and generalists that visit multiple large plant families (broad diet breadth). Understanding the evolution of sensory systems associated with changes in the detection, discrimination, and gustation of different pollen in bees can shed light on the underlying genetic mechanisms associated with transitions between narrow and broad diet breadths. We conducted a comparative study of three families of insect olfactory receptor genes (odorant receptors (ORs), gustatory receptors (GRs), and ionotropic receptors (IRs)) linked to diet breadth across 51 bee species. We calculated rates of gene gains and losses and identified genes experiencing positive selection across specialist and generalist bees. Our results show that broad generalists exhibit high rates of OR gene losses and GR gene gains. We observed accelerated rates of evolution in seven orthologous groups of genes across specialists and one group in generalists. Several orthogroups showed diversification in putative ligand-binding domains of proteins, indicating potential shifts in functional properties of the receptors. Taken together, these results indicate that dietary specialization in bees requires chemosensory system diversification of existing genes while dietary generalization is associated with the loss of ORs and gain of GRs. Our study provides important insights into the genetic architecture underlying shifts in niche occupancy across insects. 
    more » « less
  4. ; ; ; ; (, Insect Conservation and Diversity)
    Abstract Wild bees are widely believed to be in decline, yet most species remain unassessed for IUCN extinction risk. Geographic range size is used in risk assessments under the assumption that species with smaller ranges are more vulnerable to anthropogenic impacts. Narrow diet breadth can also increase vulnerability but is not currently incorporated into assessments.Niche breadth theory predicts a positive association between range size and diet breadth, which could concentrate risk among dietary specialists, but this relationship is not well established for bees and may differ among taxa.Here, we combined pollen‐use data from natural history collections with global occurrence records to test the relationship between diet breadth and range size across bees and among bee families. We assigned diet breadth using three metrics (categorical, numerical and phylogenetic) and estimated range size as the extent of occurrence for 633 species from six families.Across bees, range size increased with diet breadth, and diet specialists tended to occupy smaller ranges. These results suggest that range size and diet breadth jointly contribute to increased vulnerability in bees, indicating that some specialist species may merit conservation prioritisation.Our findings support the integration of trait‐based approaches for assessing extinction risk and highlight the high value of natural history data in identifying patterns of vulnerability among pollinators. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; (, Proceedings of the National Academy of Sciences)
    Characterizing niche space is critical for predicting species interactions and responses to environmental change. To enhance our understanding of dietary niche breadth, we used DNA metabarcoding to examine how diets of a widespread, model herbivore (woodrats, genusNeotoma) respond to changing resources and the extent to which dietary specialization is conserved across space and time. We used diet data from 13 species, 57 populations, and over 500 individuals to examine predictors of niche breadth and interindividual diet variation at a landscape scale. Then, to test whether these patterns are conserved across scales, we explored the same questions using a single population sampled over 5 y and mark-recapture data from individuals sampled at least three times. We found that woodrats exhibited a continuum of dietary specialization that included species-level dietary generalists and specialists. Specialist species maintained narrow population-level niche breadths with little evidence of interindividual diet variation. In contrast, generalist species consisted of populations with varying degrees of dietary specialization and interindividual diet variation. Across sampling scales, increased population-level niche breadth was explained by both increased interindividual diet variation and increased diet richness. These results are consistent with the Niche Variation Hypothesis and suggest that diet breadth is constrained by costs of both specialization and generalization. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Text Encoded Conversion
  • XML
  • Save / Share this Record
  • Send to Email