Habitat loss often reduces the number of species as well as functional diversity. Dramatic effects to species composition have also been shown, but changes to functional composition have so far been poorly documented, partly owing to a lack of appropriate indices. We here develop three new community indices (i.e. functional integrity, community integrity of ecological groups and community specialization) to investigate how habitat loss affects the diversity and composition of functional traits and species. We used data from more than 5000 individuals of 137 bird species captured in 57 sites in the Brazilian Atlantic Forest, a highly endangered biodiversity hotspot. Results indicate that habitat loss leads to a decrease in functional integrity while measures of functional diversity remain unchanged or are even positively affected. Changes to functional integrity were caused by (i) a decrease in the provisioning of some functions, and an increase in others; (ii) strong within-guild species turnover; and (iii) a replacement of specialists by generalists. Hence, communities from more deforested sites seem to provide different but not fewer functions. We show the importance of investigating changes to both diversity and composition of functional traits and species, as the effects of habitat loss on ecosystem functioning may be more complex than previously thought. Crucially, when only functional diversity is assessed, important changes to ecological functions may remain undetected and negative effects of habitat loss underestimated, thereby imperiling the application of effective conservation actions.
While fluctuating asymmetry (FA; small, random deviations from perfect symmetry in bilaterally symmetrical traits) is widely regarded as a proxy for environmental and genetic stress effects, empirical associations between FA and stress are often weak or heterogeneous among traits. A conceptually important source of heterogeneity in relationships with FA is variation in the selection history of the trait(s) under study, i.e. traits that experienced a (recent) history of directional change are predicted to be developmentally less stable, potentially through the loss of canalizing modifiers. Here we applied X-ray photography on museum specimens and live captures to test to what extent the magnitude of FA and FA-stress relationships covary with directional shifts in traits related to the flight apparatus of four East-African rainforest birds that underwent recent shifts in habitat quality and landscape connectivity. Both the magnitude and direction of phenotypic change varied among species, with some traits increasing in size while others decreased or maintained their original size. In three of the four species, traits that underwent larger directional changes were less strongly buffered against random perturbations during their development, and traits that increased in size over time developed more asymmetrically than those that decreased. As we believe that spurious relationships due to biased comparisons of historic (museum specimens) and current (field captures) samples can be ruled out, these results support the largely untested hypothesis that directional shifts may increase the sensitivity of developing traits to random perturbations of environmental or genetic origin.
SUMMARYIt remains largely unknown which factors affect the innate immune responses of free-living birds. Nevertheless, the degree of innate immunity may play a crucial role in an individual's survival as it procures the first defence against pathogens. We manipulated the ectoparasite load of great tit (Parus major) nests by infesting them with hen fleas (Ceratophyllus gallinae) before egg laying. We subsequently quantified natural antibody (NAb) concentration and complement activation in nestlings and adult females during breeding and post-breeding periods. NAb concentrations increased in nestlings and adult females breeding in flea-infested nest boxes during the nestling provisioning period, but not in breeding females during incubation. In contrast, parasite abundance did not affect levels of complement activity in females. NAb levels of nestlings were already fully developed at the end of the nestling stage, but complement activation was only observed post-fledging. Concentrations of NAbs and complement activation of adult females were significantly lower during the breeding season compared with post-breeding levels, but did not differ between incubation and chick rearing. Further experimental studies in species that vary in life-history strategies will allow us to unravel the mechanisms underlying the observed variation in innate immune defences.
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