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1. Contrasting latitudinal gradients of body size in helminth parasites and their hosts

   https://doi.org/10.1111/geb.12894  

   Dallas, Tad ; Gehman, Alyssa‐Lois M. ; Aguirre, A. Alonso ; Budischak, Sarah A. ; Drake, John M. ; Farrell, Maxwell J. ; Ghai, Ria ; Huang, Shan ; Morales‐Castilla, Ignacio ; Keith, ed., Sally ( February 2019 , Global Ecology and Biogeography)

   We examined body size scaling relationships for two developmental life stages of parasitic helminths (egg and adult) separately in relationship to latitude (i.e. Bergmann's rule), temperature and temperature seasonality. Given that helminth eggs experience environmental conditions more directly, whereas adults live inside infected host individuals, we predict stronger environmentally driven gradients of body size for eggs than for adults.

   Global.

   Present day.

   Parasitic helminths.

   We compiled egg size and adult body size data (both minimum and maximum) for 265 parasitic helminth species from the literature, along with species latitudinal distribution information using an extensive global helminth occurrence database. We then examined how the average helminth egg and adult body size of all helminth species present (minimum and maximum separately) scaled with latitude, temperature and temperature variability, using generalized linear models.

   Both the egg size and the adult body size of helminths tended to decrease towards higher latitudes, although we found the opposite body size scaling pattern for their host species. Helminth sizes were also positively correlated with temperature and negatively, but more weakly, with temperature seasonality.

   Instead of following the body size patterns of their hosts, helminth parasites are more similar to other ectotherms in that they follow the converse Bergmann's rule. This pattern did not differ between helminth developmental stages, suggesting that mean annual temperature and seasonality are unlikely to be related mechanistically to body size variation in this case.

    

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2. The biotic interactions hypothesis partially explains bird species turnover along a lowland Neotropical precipitation gradient

   https://doi.org/10.1111/geb.13047  

   Gomez, Juan Pablo ; Ponciano, José Miguel ; Londoño, Gustavo A. ; Robinson, Scott K. ; Fleishman, ed., Erica ( December 2019 , Global Ecology and Biogeography)

   We evaluated the influence of climate on the structure of bird communities along precipitation gradients. We hypothesize that mechanisms responsible for community turnover along precipitation gradients are similar to mechanisms operating along temperature and latitudinal gradients. We tested the hypothesis that environmental conditions affect community composition in dry forests, whereas biotic interactions affect community composition in wet forests.

   Low‐elevation forests along a precipitation gradient in Colombia where precipitation ranges from 700–4,000 mm annually but elevation and temperature remain constant.

   Present day.

   Neotropical forest birds.

   We sampled at 291 points in nine study areas (localities) across thec. 3,000‐mm precipitation range. In each locality, we obtained climatic characteristics and phylogenetic, morphological and physiological proxy data to test predictions about the evolutionary relationships and distribution of traits.

   Bird communities changed abruptly along the precipitation gradient and differed between dry and wet forests. Analyses of phylogenetic relationships, trait space, and observations at nests suggested that environmental filtering is more important in dry than in wet forests, especially for breeding. In contrast, we found little evidence that competition was more important in wet than in dry forests. Nest predation or competition for nest space, however, may be more critical in wetter forests.

   The two distinct bird communities we documented suggest that lowland precipitation gradients, across which temperature is constant, can be as important as temperature gradients in generating high beta diversity. We conclude that breeding in bird communities might be crucial for determining community assembly along environmental gradients. Given that recent population declines in tropical birds have been attributed to changes in precipitation, by understanding the mechanisms underlying community assembly along precipitation gradients our study may improve our ability to understand those declines and predict the effects of climate change on Neotropical avifauna.

    

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3. The island biogeography of the eBird citizen‐science programme

   https://doi.org/10.1111/jbi.14026  

   La Sorte, Frank A. ; Somveille, Marius ( December 2020 , Journal of Biogeography)

   Island biotas face an array of unique challenges under global change. Monitoring and research efforts, however, have been hindered by the large number of islands, their broad distribution and geographical isolation. Global citizen‐science initiatives have the potential to address these deficiencies. Here, we determine how the eBird citizen‐science programme is currently sampling island bird assemblages annually and how these patterns are developing over time.

   Global.

   Birds.

   We compiled occurrence information of non‐marine bird species across the world's islands (n = 21,813) over an 18‐year period (2002–2019) from eBird. We estimated annual survey completeness and species richness across islands, which we examined in relation to six geographical and four climatic features.

   eBird contained bird occurrence information forca. 20% of the world's islands (n = 4,205) withca. 8% classified as well surveyed annually (n = 1,644). eBird participants tended to survey larger islands that were more distant from the mainland. These islands had lower proximity to other islands and contained a broader range of elevations. Temperature, precipitation and temperature seasonality were at intermediate levels. Precipitation seasonality was at low and intermediate levels. Islands located between 10 and 60° N latitude and 20 and 40° S latitude were overrepresented, and islands located in Southeast Asia were underrepresented. From 2002 to 2019, the number of islands surveyed annually increased byca. 96.4 islands/year. During this period, island size decreased, distance from mainland did not change, proximity to other islands increased and elevation range decreased.

   The eBird programme tends to survey larger islands containing intermediate climates that are more isolated from the mainland and other islands. These findings provide a framework to support the informed application of the eBird database in avian island biogeography. Our findings emphasize citizen science as an empirical resource to support long‐term ecological research, conservation and monitoring efforts across remote regions of the globe.

    

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4. Intraspecific variation in incubation behaviours along a latitudinal gradient is driven by nest microclimate and selection on neonate quality

   https://doi.org/10.1111/1365-2435.13772  

   Lundblad, Carl G. ; Conway, Courtney J. ; Sandercock, ed., Brett ( March 2021 , Functional Ecology)

   The strategies by which animals allocate reproductive effort across their lifetimes vary, and the causes of variation in those strategies are actively debated. In birds, most research has focused heavily on variation in clutch size and fecundity, but incubation behaviour and other functionally related traits have received less attention. Variation in incubation period duration is notable because time‐dependent sources of clutch mortality should impose strong directional selection to minimize the incubation period. However, life‐history theory predicts multiple mechanisms by which inter‐ and intraspecific variation in incubation behaviours may be adaptive.

   We conducted one of the first studies of intraspecific latitudinal variation in avian incubation behaviours across a large portion of a single species’ range. We placed motion‐activated nest cameras inside burrowing owl nests at five study sites to quantify variation in daily nest attentiveness, cumulative nest attendance and incubation period duration. We tested predictions of two alterative hypotheses that have been proposed to explain variation in incubation periods: theparental risk tolerance hypothesisand theneonate quality hypothesis.

   Daily nest attentiveness, cumulative nest attendance and incubation period duration in burrowing owls were all positively correlated with latitude. Burrowing owls reduced their daily nest attentiveness at low latitudes and on days when the average nest temperature was within the range that is optimal for embryo development. Further, longer incubation periods were most strongly associated with greater cumulative nest attendance instead of reduced daily nest attentiveness.

   These results support predictions of theneonate quality hypothesis:longer incubation periods result from stronger selection on neonate quality rather than selection to reduce reproductive effort in response to low extrinsic mortality risk. However, some owls facultatively reduced their daily nest attentiveness, and this result supports the general hypothesis that incubation decisions reflect a trade‐off between reproduction and self‐maintenance, and that the optimal solution to that trade‐off varies systematically in response to latitudinal gradients in adult mortality.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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5. Temporal changes in the individual size distribution modulate the long‐term trends of biomass and energy use of North American breeding bird communities

   https://doi.org/10.1111/geb.13777  

   Diaz, Renata M. ; Ernest, S. K. Morgan ( October 2023 , Global Ecology and Biogeography)

   The frequency of different body sizes in an ecological community (the individual size distribution, or ISD) is a key link between the number of individual organisms present in a community and community function—total biomass or total energy use. If the ISD changes over time, the dynamics of community function may become decoupled from trends in abundance. Understanding how, and how often, the ISD modulates the relationship between abundance, biomass and energy use is of critical importance to understand biodiversity trends in the Anthropocene. Here, we conduct the first macroecological‐scale analysis of this type for avian communities.

   North America, north of Mexico.

   1989–2018.

   Breeding birds.

   We used species' traits to generate annual ISDs for bird communities in the North American Breeding Bird Survey. We compared the long‐term trends in total biomass and energy use to the trends generated from a null model of an unchanging ISD.

   Trends in biomass have been evenly split between increases and decreases, but the trends predicted by the null model were dominated by decreases. A substantial number of communities have undergone a shift in the ISD favouring larger bodied species, resulting in a less negative trend in biomass than would be expected had the ISD remained static. Trends in energy use more closely paralleled the null model.

   Taking changes in the ISD into account qualitatively changes the continental‐scale picture of how biomass and energy use have changed over the past 30 years. For North American breeding birds, shifts in species composition favouring larger bodied species may have partially offset declines in standing biomass driven by losses of individuals over the past 30 years.

    

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