Esta es la versión de autor del artículo publicado en: This is an author produced version of a paper published in:Behavioral Ecology and Sociobiology 69.9 (2015): 1493-1500 DOI: http://dx.doi.org/10.1007/s00265-015-1961-6 Copyright: © 2015 Springer VerlagEl acceso a la versión del editor puede requerir la suscripción del recurso Access to the published version may require subscriptionThe intensity of male-male interactions declines in highland songbird populations AbstractElevation gradients are associated with sharp environmental clines that play a crucial role in the phenotypic diversification of animal populations. In a variety of organisms, the reproductive output of females declines with elevation in parallel to the drop in environmental productivity and shortening of the breeding season. Little evidence is available on male traits associated with reproductive activities, such as territorial defence and signalling, which may decline because of the low economic defendability of resources and the selective advantage of investing in parental rather than mating (e.g. signalling, chasing intruders) effort in such conditions. Along a broad elevational gradient, we investigated variation in the intensity of territorial defence and sexual signalling in males of the water pipit Anthus spinoletta exposed to song playbacks simulating the territorial intrusion of a conspecific. We found that birds from the lower limits of the species distribution approached song stimuli more closely than those from the upper limits. Moreover, physically challenging songs (broad frequency bandwidths and fast trills) elicited a closer approach, and low elevation birds uttered songs ending with the broadest bandwidths. Other responses to the intrusion, such as the number of songs uttered or the latency to approach, exhibited seasonal or spatial variation irrespective of elevation. This study illustrates the decline of some trait associated with aggressive territorial behaviours during male-male conflicts along elevation, and points to the allocation in sexual signalling and motor constraints to signal production, as potential mechanisms underlying it.

Predator-prey interactions play a key role in the success and impacts of invasive species. However, the effects of invasive preys on native predators have been poorly studied. Here, we first reviewed hypotheses describing potential relationships between native predators and invasive preys. Second, we examined how an invasive prey, the Argentine ant (Linepithema humile), affected a native terrestrial amphibian community. In the field, we looked at the structure of the amphibian community in invaded versus uninvaded areas and characterized amphibian trophic ecology. The amphibian community sampled seemed to show a species-dependent response in abundance to invasion: adults of the natterjack toad (Bufo calamita), the species demonstrating the highest degree of ant specialization, were less abundant in invaded areas. Although available ant biomass was significantly greater in invaded than in uninvaded areas (only Argentine ants occurred in the former), amphibians consumed relatively fewer ants in invaded areas. In the lab, we quantified amphibian consumption of Argentine ants versus native ants and assessed whether consumption patterns could have been influenced by prior exposure to the invader. The lab experiments corroborated the field results: amphibians preferred native ants over Argentine ants, and prior exposure did not influence consumption. Differences in preference explained why amphibians consumed fewer Argentine ants in spite of their greater relative availability; they might also explain why the most ant-specialized amphibians seemed to avoid invaded areas. Our results suggest the importance to account for predator feeding capacities and dietary ranges to understand the effects of invasive species at higher trophic levels.

Invasive species have major impacts on biodiversity and are one of the primary causes of amphibian decline and extinction. Unlike other top ant invaders that negatively affect larger fauna via chemical defensive compounds, the Argentine ant (Linepithema humile) does not have a functional sting. Nonetheless, it deploys defensive compounds against competitors and adversaries. We estimated levels of ant aggression toward 3 native terrestrial amphibians by challenging juveniles in field ant trails and in lab ant foraging arenas. We measured the composition and quantities of toxin in L. humile by analyzing pygidial glands and whole‐body contents. We examined the mechanisms of toxicity in juvenile amphibians by quantifying the toxin in amphibian tissues, searching for histological damages, and calculating toxic doses for each amphibian species. To determine the potential scope of the threat to amphibians, we used global databases to estimate the number, ranges, and conservation status of terrestrial amphibian species with ranges that overlap those of L. humile. Juvenile amphibians co‐occurring spatially and temporally with L. humile die when they encounter L. humile on an ant trail. In the lab, when a juvenile amphibian came in contact with L. humile the ants reacted quickly to spray pygidial‐gland venom onto the juveniles. Iridomyrmecin was the toxic compound in the spray. Following absorption, it accumulated in brain, kidney, and liver tissue. Toxic dose for amphibian was species dependent. Worldwide, an estimated 817 terrestrial amphibian species overlap in range with L. humile, and 6.2% of them are classified as threatened. Our findings highlight the high potential of L. humile venom to negatively affect amphibian juveniles and provide a basis for exploring the largely overlooked impacts this ant has in its wide invasive range.

The consequences of ant invasions on ecosystems may only become apparent after long periods. In addition, predicting how sensitive native fauna will respond is only possible if the underlying proximate mechanisms of their impact are identified. We studied the attraction of the native and invasive ant community to artificial bird nests. Further, we studied reproduction of a wild native songbird over five consecutive breeding seasons in relation to the presence of an invasive ant species. We analysed biometric, reproductive and individual blood parameters of great tits Parus major breeding in invaded as compared to uninvaded sites by Argentine ants Linepithema humile . Great tits bred preferably in uninvaded territories by the Argentine ant. Moreover, Argentine ants were more abundant at nests in invaded sites, than any native ant species were at uninvaded sites. Further, Argentine ants recruited at the artificial nests more intensively and responded to a larger variety of nest contents than native species. Although breeding success and adult condition did not vary in relation to invasion status, offspring quality was negatively affected by the presence of Argentine ants. Nestlings reared in invaded sites were lighter, with lower wing/tarsus length ratio and had a reduced nutritional condition and altered oxidative stress balance as measured from several blood parameters. The interspersed distribution and small distance between invaded vs. uninvaded territories suggest that ant presence affects nestling condition through direct interference at the nest. Our results highlight Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporationthe importance of evaluating the proximate effects like physiological parameters of the native fauna, when studying invasive ant-native bird interactions. Response to Reviewers:Reviewer #1: This is an excellent manuscript that deserves to be published. Congratulations on producing a fine scientific work! Response: Thank you very much. I recommend that you include a paragraph somewhere in the Introduction or Methods section that summarizes the native range and introduced range of the Argentine Ant and the native range of the Great Tit. This paragraph should also tell when the Argentine Ant was first introduced into Spain and what date it invaded the Doñana Biological Reserve. Because most of the readers of this journal study alien invasive species and biological invasions, they will want to know such information and it will help them to quickly orientate themselves to the species and the concepts studied. I realize that a few readers already know this information, but I would guess that many do not. Remember, Biological Invasions is a global journal with readers around the world, many living in areas where the Argentine Ant or Great Tit, or both species, do not occur.Response. We have now restructured the last two paragraphs of the introduction to address this issue (Ln 99-109, 110-122), following both reviewers' advice.Reviewer #2: Overall, this study will be of ...