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1. High variation in handling times confers 35‐year stability to predator feeding rates despite community change

   https://doi.org/10.1002/ecy.3954  

   Novak, Mark ( January 2023 , Ecology)

   Historical resurveys of ecological communities are important for placing the structure of modern ecosystems in context. Rarely, however, are snapshot surveys alone sufficient for providing direct insight into the rates of the ecological processes underlying community functioning, either now or in the past. In this study, I used a statistically reasoned observational approach to estimate the feeding rates of a New Zealand intertidal predator,Haustrum haustorium, using diet surveys performed at several sites by Robert Paine in 1968–1969 and by me in 2004. Comparisons between time periods reveal a remarkable consistency in the predator's prey‐specific feeding rates, which contrasts with the changes I observed in prey abundances, the predator's body‐size distribution, and the prey's proportional contributions to the predator's apparent diet. Although these and additional changes in the predator's per‐capita attack rates seem to show adaptive changes in its prey preferences, they do not. Rather, feeding‐rate stability is an inherently statistical consequence of the predator's high among‐prey variation in handling times which determine the length of time that feeding events will remain detectable to observers performing diet surveys. Though understudied, similarly high among‐prey variation in handling (or digestion) times is evident in many predator species throughout the animal kingdom. The resultant disconnect between a predator's apparent diet and its actual feeding rates suggests that much of the temporal, biogeographic, and seemingly context‐dependent variation that is often perceived in community structure, predator diets, and food‐web topology may be of less functional consequence than assumed. Qualitative changes in ecological pattern need not represent qualitative changes in ecological process.

    

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2. Gradual and Discrete Ontogenetic Shifts in Rattlesnake Venom Composition and Assessment of Hormonal and Ecological Correlates

   https://doi.org/10.3390/toxins12100659  

   Schonour, Richard B. ; Huff, Emma M. ; Holding, Matthew L. ; Claunch, Natalie M. ; Ellsworth, Schyler A. ; Hogan, Michael P. ; Wray, Kenneth ; McGivern, James ; Margres, Mark J. ; Colston, Timothy J. ; et al ( October 2020 , Toxins)

   null (Ed.)

   Ontogenetic shifts in venom occur in many snakes but establishing their nature as gradual or discrete processes required additional study. We profiled shifts in venom expression from the neonate to adult sizes of two rattlesnake species, the eastern diamondback and the timber rattlesnake. We used serial sampling and venom chromatographic profiling to test if ontogenetic change occurs gradually or discretely. We found evidence for gradual shifts in overall venom composition in six of eight snakes, which sometimes spanned more than two years. Most chromatographic peaks shift gradually, but one quarter shift in a discrete fashion. Analysis of published diet data showed gradual shifts in overall diet composition across the range of body sizes attained by our eight study animals, while the shifts in abundance of different prey classes varied in form from gradual to discrete. Testosterone concentrations were correlated with the change in venom protein composition, but the relationship is not strong enough to suggest causation. Venom research employing simple juvenile versus adult size thresholds may be failing to account for continuous variation in venom composition lifespan. Our results imply that venom shifts represent adaptive matches to dietary shifts and highlight venom for studies of alternative gene regulatory mechanisms. 

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3. Head shape predicts isotopic diet in anoles and day geckos

   https://doi.org/10.1111/1365-2435.14331  

   Figueira, Tyler J. ; Kennedy‐Gold, Stevie ; Piantoni, Carla ; Screen, Robyn M. ; Wright, Amber N. ( April 2023 , Functional Ecology)

   Trophic morphology affects resource acquisition; therefore, species differences in such traits may be informative for inferring resource use overlap and potential species interactions.

   In lizards, head size and shape determine the size and hardness of prey that can be consumed. Lizards with large differences in head morphology are expected to overlap less in prey use than lizards with more similar traits.

   Stable isotopes are increasingly being used to describe diet, yet how traditional functional traits affect isotopic diet is often not clear a priori.

   We measured head size, head shape, 𝛿¹⁵N, and 𝛿¹³C under controlled resource availability in an enclosure experiment using introduced lizards in Hawaiʻi to test whether functional traits predict isotopic diet.

   Brown anolesAnolis sagreihad the tallest and narrowest heads, the highest values of 𝛿¹³C, and the lowest values of 𝛿¹⁵N. Gold dust day geckosPhelsuma laticaudahad the shortest and widest heads, the lowest values of 𝛿¹³C, and the highest values of 𝛿¹⁵N. Green anolesAnolis carolinensiswere intermediate in both diet and morphology.

   As a result of isotopic diet overlap, green anoles have reduced competitor‐free resource space in the presence of both of the other lizard species.

   Head shape was the best predictor of diet and the only trait that explained variation within as well as among species. Head size was sexually dimorphic, and therefore the weaker diet correlations with this trait may be explained by sexual selection.

   Breadth in morphospace did not correlate with isotopic diet breadth, nor did the amount of overlap in morphospace predict the amount of overlap in isotopic diet space.

   While lizards were able to locally depress prey in experimental enclosures, no shifts in diet were detected in response to the presence of heterospecifics.

   The generality of head shape in predicting isotopic diet, and whether it does so independent of habitat use, warrants additional study. Head shape provides a potentially fruitful avenue for trait‐based approaches to studying ecology and evolution in lizards.

   Read the freePlain Language Summaryfor this article on the Journal blog.

    

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4. Variation in brown rat cranial shape shows directional selection over 120 years in New York City

   https://doi.org/10.1002/ece3.6228  

   Puckett, Emily E. ; Sherratt, Emma ; Combs, Matthew ; Carlen, Elizabeth J. ; Harcourt‐Smith, William ; Munshi‐South, Jason ( April 2020 , Ecology and Evolution)

   Urbanization exposes species to novel environments and selection pressures that may change morphological traits within a population. We investigated how the shape and size of crania and mandibles changed over time within a population of brown rats (Rattus norvegicus) living in Manhattan, New York, USA, a highly urbanized environment. We measured 3D landmarks on the cranium and mandible of 62 adult individuals sampled in the 1890s and 2010s. Static allometry explained approximately 22% of shape variation in crania and mandible datasets, while time accounted for approximately 14% of variation. We did not observe significant changes in skull size through time or between the sexes. Estimating the P‐matrix revealed that directional selection explained temporal change of the crania but not the mandible. Specifically, rats from the 2010s had longer noses and shorter upper molar tooth rows, traits identified as adaptive to colder environments and higher quality or softer diets, respectively. Our results highlight the continual evolution to selection pressures. We acknowledge that urban selection pressures impacting cranial shape likely began in Europe prior to the introduction of rats to Manhattan. Yet, our study period spanned changes in intensity of artificial lighting, human population density, and human diet, thereby altering various aspects of rat ecology and hence pressures on the skull.

    

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5. Bird predation and landscape context shape arthropod communities on broccoli

   https://doi.org/10.1093/ornithapp/duac005  

   Taylor, Joseph M. ; Smith, Olivia M. ; Edworthy, Max ; Kennedy, Christina M. ; Latimer, Christopher E. ; Owen, Jeb P. ; Wilson-Rankin, Erin E. ; Snyder, William E. ( February 2022 , Ornithological Applications)

   Birds increase crop yields via consumption of pests in some contexts but disrupt pest control via intraguild predation in others. Landscape complexity acts as an inconsistent mediator, sometimes increasing, decreasing, or not impacting pest control. Here, we examined how landscape context and seasonal variation mediate the impact of birds on arthropod pests and natural enemies, leaf damage, and yields of broccoli (Brassica oleracea) on highly diversified farms that spanned the USA west coast. Our study had two complementary components: a bird exclusion experiment and molecular diet analysis of 357 fecal samples collected from the most commonly captured bird species that also foraged in Brassica fields—American Goldfinch (Spinus tristis), American Robin (Turdus migratorius), Savannah Sparrow (Passerculus sandwichensis), Song Sparrow (Melospiza melodia), and White-crowned Sparrow (Zonotrichia leucophrys). Bird access yielded higher, rather than lower, numbers of pest aphids and increased their parasitism, while no other arthropods examined were consistently impacted. Independent of bird presence, percent natural cover in the landscape sometimes increased and sometimes decreased densities of arthropods in the mid-growth period, with diminishing impacts in the late-growth period. Herbivore feeding damage to broccoli leaves decreased with increasing amounts of natural land cover and in the late-growth period. Molecular diet analysis revealed that Brassica pests and predatory arthropods were relatively uncommon prey for birds. Landscape context did not alter the prey items found in bird diets. Altogether, our bird-exclusion experiment and molecular diet analysis suggested that birds have relatively modest impacts on the arthropods associated with broccoli plantings. More broadly, the limited support in our study for net natural pest control services suggests that financial incentives may be required to encourage the adoption of bird-friendly farming practices in certain cropping systems.

    

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