Competencia por el alimento entre el cormorán moñudo, el cormorán grande y la pesca artesanal: un caso de estudio

The Mediterranean shag (Phalacrocorax aristotelis desmarestii) and the great cormorant (P. carbo sinensis) are syntopic birds in an area encompassing Grosa Island and the Mar Menor coastal lagoon (SE Spain, western Mediterranean) during the breeding season of the former and the wintering period of the latter. Diet composition of both birds was studied through pellet analysis and otolith identification. Competition for fish resources between these two seabirds and with local artisanal fisheries was assessed. Shags preyed preferentially on small pelagic fish, and great cormorants mainly consumed demersal fish. Shag diet consisted of marine fish strictly, but great cormorant fed in all the available environments in the study area, including marine, transitional (coastal lagoon) and freshwater reservoirs. The great dissimilarity observed between shag and great cormorant diet composition showed no competition between them. The low shag population density and fishing effort in their foraging area suggested no competition with fisheries. Conversely, great cormorant population density in the study area was very high, and they foraged on fish of high commercial value. However, competition between great cormorant and artisanal fisheries only affected some of the less abundant species fished.El cormorán moñudo (Phalacrocorax aristotelis desmarestii) y el cormorán grande (P. carbo sinensis) son especies sintópicas en el entorno de Isla Grosa y la laguna costera del Mar Menor (SE de España, Mediterráneo occidental) durante la época de reproducción del primero que coincide con la invernada del segundo. Se estudia la composición de la dieta de ambas especies mediante la identificación de otolitos en sus egagrópilas, y se evalúa la competencia entre ambas especies y con la pesca artesanal local. El cormorán moñudo se alimentó mayoritariamente de pequeños peces pelágicos, y el cormorán grande consumió principalmente peces demersales. La dieta del cormorán moñudo consistió estrictamente de peces marinos, mientras que el cormorán grande capturó peces en los diferentes ambientes acuáticos de la zona de estudio, incluyendo especies marinas, de lagunas costeras e incluso de embalses de agua dulce. La gran disimilitud observada entre la composición de la dieta de ambas aves nos indica que no existe competencia por el alimento entre ellas. Asimismo, la baja densidad poblacional de cormorán moñudo y su esfuerzo pesquero en la zona de estudio tampoco demuestran competencia con la pesca artesanal local. Por el contrario, la abundancia de cormorán grande en la zona de estudio es muy alta, y se alimentaron principalmente de especies de alto valor comercial para los pescadores locales. No obstante, solo se observó competencia con la pesca artesanal local por alguna especie de pez de las menos abundantemente capturadas por los pescadores

Data from: Evaluating temporal turnover in avian species richness in a Mediterranean semiarid region: different responses to elevation and forest cover

<p><span><strong>Aim</strong>.</span><span> When studying the effects of global change on biodiversity, it is far more common for the effects of climate change and land-use changes to be assessed separately rather than jointly. However, the effects of land-use changes in recent decades on species richness in areas affected by climate change have been less studied. </span><span>We assess the temporal turnover in species richness of an avian community between a historical period and a modern one as a consequence of global change.</span></p> <p><span><strong>Location</strong>. </span><span>Semiarid Mediterranean ecosystem (Southeastern Spain). </span></p> <p><span><strong>Method</strong>.</span><span> We fitted a hierarchical multi-species occupancy </span><span>model for each period (</span><span>1991-1992, and 2012-2017)</span><span>, obtaining avian species-specific estimates of occupancy probability in relation to environmental covariates </span><span>(elevation and forest cover)</span><span>. </span><span>We analyze the relationships between changes in the bird community and environmental variables, analysing the temporal turnover of the species richness and the richness-based species-exchange ratio.</span> </p> <p><span><strong>Results</strong>.</span> <span>The estimated species richness accounting for detectability was higher than observed species richness, and decreased in the </span><span>more recent </span><span>period. Following our hypotheses, we observed a dual pattern of species richness increase associated with different elevations, showing different species turnover rates due to the joint effects of climate change and land-use change. There is a trend toward greater species richness with higher elevations that is associated with climate change, where the species turnover rate is low. Also, species richness increased towards lower elevations, but with a high turnover rate. The latter can be due to species expansions through</span><span>ou</span><span>t new habitat configurations in bordering forest systems associated with anthropic land-use changes. </span></p> <p><span><strong>Conclusions</strong>.</span><span> Our study is of great interest to understand the temporal turnover of avian species richness associated with areas experiencing both climate and land-use change.</span></p><p>Funding provided by: Spanish Ministry of Economy and Competitiveness*<br>Crossref Funder Registry ID: <br>Award Number: IJC2019-039145-I</p><p><span>This field work was developed as a basis for assessing the state of the region's forest heritage and the effects of global change on its biodiversity</span><span>, concentrated in two periods: a "historical period" (years 1991 and 1992) and a "modern period" (years 2012 and 2017). The survey protocol was characterized by transects of 1 kilometer length, which were distributed across all the forested areas in the study area in a random fashion and were surveyed once during a breeding period (May-July)</span><span>. Each transect survey was conducted by walking and recording the number of each species detected (by sight or song/call) along it. A total of 377 1-km transects were conducted for the historical period as part of a forestry plan in the region, developing a new avian survey of 198 transects with a similar protocol for the modern period.</span></p> <p><span>We considered the 1-km transects of each bird survey as nested within a "site", i.e., as spatial observations replicated within the site, thus enabling estimation of detection probability in an occupancy model</span><span>. We defined sites as cells in a grid that covers our study area</span><span>. We selected cell size to be 2x2 km, based on the species in our bird community (most of them passerines with small home ranges</span><span>)</span><span>, which may be suitable for evaluating the effects of environmental covariates on bird species occupancy at a regional scale</span><span>. </span><span>Therefore, a total of 377 and 198 1-km spatial transects were conducted and grouped in 226 and 139 sites for the historical and modern periods, respectively. </span></p&gt