Showing papers by "Francisco S. Tortosa published in 2014"

Is the effect of farming practices on songbird communities landscape dependent? A case study of olive groves in southern Spain

Abstract: Extensive farming practices and landscape heterogeneity promote biodiversity in agroecosystems. However, the effect of such practices might be landscape dependent; specifically, the effect might be greatest where the loss of heterogeneity has been the largest. In recent decades, agricultural intensification and landscape simplification have dramatically affected the Mediterranean region, where olive groves are one of the predominant crops. For instance, in Spain from 1996 to 2008, the amount of land dedicated to olive groves increased by 300,000 ha (12 %). In conventional olive farming, herbicides are applied intensively to minimize competition between crops and swards for water; however, to prevent erosion, many farmers are maintaining swards within crops. This practice likely benefits farmland biodiversity, although the heterogeneity of the surrounding landscape might influence the extent of these effects. This study assessed the effects of herbaceous cover on the abundance and species richness of songbird communities in six matched pairs of olive groves (ground cover or bare ground) in homogeneous and heterogeneous landscapes over a 3-year period. We predicted that (1) the presence of ground cover and landscape heterogeneity would have a positive effect on songbird communities, and (2) the effect would be greatest in homogeneous environments. Although bird community composition differed among landscape types and farming practices in the olive groves in southern Spain, the effect of ground cover was not landscape dependent. The presence of ground cover had a positive effect on the abundance and richness of songbirds, including sensitive species, but landscape heterogeneity did not have an effect. This study underscores the important role of agricultural practices in preserving farmland bird communities, while it also suggests that landscape heterogeneity might not be very important in Mediterranean perennial farming systems. The positive effects of ground cover can be important for preserving the wintering quarters of numerous European bird species, including species of conservation concern.

Predation of simulated red-legged partridge nests in big game estates from South Central Spain

Abstract: Over the past few decades, the wild boar has been undergoing an expansion in Europe, which may have negatively affected small game populations and particularly red-legged partridges. We aim to evaluate the red-legged partridge nest predation by wild boar at high boar abundances by placing artificial nests in nine big game estates. Predation rates were compared between nests placed in fenced controlled plots with no wild boar access (but accessible to other predators) and open plots in which the wild boar gains access. The proportion of nests and eggs predated was significantly lower in wild boar exclusion areas, recording a predation rate of 50 % for the nests and 38 % for the eggs in these areas, whereas in the presence of wild boar, the predation rate was 80 % for the nests and 58 % for the eggs. Moreover, the wild boar was identified as the main nest predator in unfenced areas, accounting for 36 and 48 % of the predated nests and eggs respectively. This study sheds light on the wild boar predation on nests of the red-legged partridges.

The high abundance of wild ungulates in a Mediterranean region: is this compatible with the European rabbit?

Abstract: The landscape in southern Iberia has, over the last four decades, altered as a result of the land abandonment, while the abundance of wild boar Sus scrofa and red deer Cervus elaphus has simultaneously increased, and some key prey species such as the European rabbit Oryctolagus cuniculus have declined. In this work we explore: 1) the relationships between big game species (red deer and wild boar) and rabbit abundance, and 2) whether these relationships could have effects on food quality (total nitrogen available in the pasture and percentage of leguminosae) and food availability of (herbaceous cover). We therefore selected nine big game estates with a range of abundance as regards ungulates and similar Mediterranean habitat. Wild boar abundance was statistically negative in relation to rabbit abundance, while no significant statistical relationships between rabbit abundance and habitat structure and forage quality were evidenced. However, wild boar abundance, but not that of red deer, was negatively assoc...

Effect of wild ungulate density on invertebrates in a Mediterranean ecosystem

Abstract: Efecto de la densidad de ungulados silvestres sobre los invertebrados en un ecosistema Mediterraneo En las ultimas decadas, la abundancia y distribucion de determinadas especies de caza mayor, especialmente el ciervo rojo (Cervus elaphus) y el jabali (Sus scrofa), han aumentado en la zona centromeridional de Espana como resultado de las estrategias de gestion cinegetica. La alta densidad de estas especies de ungulados puede afectar a la abundancia de los invertebrados epigeos. Estudiamos la relacion entre la abundancia de las especies de caza mayor y la biodiversidad, la riqueza de taxones, la biomasa de invertebrados y su frecuencia en nueve fincas de caza, y se comparo con las zonas de exclusion de ungulados. De por si, la exclusion de ungulados afecto a la riqueza de invertebrados, ya que se encontraron valores mas bajos en las parcelas abiertas, mientras que las mayores diferencias en la diversidad de invertebrados entre parcelas abiertas y cercadas se encontraron en zonas con una alta densidad de jabalies. Donde la densidad de jabalies era alta, el numero de invertebrados disminuyo, mientras que donde era baja, el ciervo rojo tuvo un efecto positivo en la abundancia de invertebrados. Asi, las parcelas cercadas parecian ofrecer refugio a los invertebrados, sobre todo donde los jabalies eran abundantes. Este estudio apoya la idea de que las poblaciones con una alta densidad de ungulados perjudican a la estructura de las comunidades faunisticas, probablemente debido a la disminucion de la disponibilidad de alimentos como consecuencia del sobrepastoreo, la modificacion de las condiciones de los micronichos ecologicos y la depredacion directa. Sin embargo, los efectos dependieron del grupo de invertebrados, ya que las especies saprofitas podrian beneficiarse de la alta abundancia de ungulados. Nuestros resultados reflejan la necesidad de controlar la densidad de las poblaciones de ungulados en condiciones mediterraneas en el suroeste de Europa y de establecer parcelas de exclusion de ungulados.

Herbaceous ground cover reduces nest predation in olive groves

Abstract: Capsule Bare ground increases artificial nest predation in olive groves.Aims To assess the effect of different soil management regimes on nest predation rates in olive groves.Methods We performed nest predation experiments with artificial nests during the breeding season in 2013, in two areas of southern Spain. Each artificial nest (n = 300) contained three quail Coturnix eggs, two of which were unmanipulated and the third one was emptied and injected with plaster. Predators were identified by marks on eggs filled with plaster.Results Ground nests were significantly more depredated, irrespective of the presence of ground cover; tree nests were less depredated in fields with ground cover. There was a clear difference in nest predators of ground and tree nests. Rodents were the most frequent predators of tree nests.Conclusion Lower predation rates of tree nests in orchards with ground cover are probably linked to a change in the foraging behaviour of rodents, which in these more complex habitats might be re...

Role of prey and intraspecific density dependence on the population growth of an avian top predator

Abstract: Exploring predator–prey systems in diverse ecosystems increases our knowledge about ecological processes. Predator population growth may be positive when conspecific density is low but predators also need areas with prey availability, associated with competition, which increases the risk of suffering losses but stabilises populations. We studied relationships between European rabbits Oryctolagus cuniculus (prey) and adult eagle owls Bubo bubo (predators) in south-western Europe. We assessed models explaining the predator population growth and stability. We estimated the abundance of rabbits and adult eagle owls during three years in eight localities of central-southern Spain. We explored models including rabbit and adult eagle owl abundance, accounting for yearly variations and including the locality as a random variable. We found that population growth of adult eagle owls was positive in situations with low conspecific abundance and tended to be negative but approaching equilibrium in situations of higher conspecific abundance. Population growth was also positively related to previous summer rabbit density when taking into account eagle owl conspecific abundance, possibly indicating that rabbits may support recruitment. Furthermore, abundance stability of adult eagle owls was positively related to previous winter–spring rabbit density, which could suggest predator population stabilisation through quick territory occupation in high-quality areas. These results exemplify the trade-off between prey availability and abundance of adult predators related to population growth and abundance stability in the eagle owl–rabbit system in south-western Europe. Despite rabbits have greatly declined during the last decades and eagle owls locally specialise on them, eagle owls currently have a favourable conservation status. As eagle owls are the only nocturnal raptor with such dependence on rabbits, this could point out that predators may overcome prey decreases in areas with favourable climate and prey in the absence of superior competitors with similar foraging mode.

High rabbit abundance proves detrimental to the population growth rate in European rabbit (Oryctolagus cuniculus L.) extensive breeding enclosures

Abstract: The European rabbit ( Oryctolagus cuniculus L.) is a key prey species in Mediterranean ecosystems that has declined in its natural ranges as a result of diseases and loss of habitat. This situation has led to the production of wild rabbits in enclosures in which they can acclimate and breed. The efficiency of these enclosures as extensive breeding systems is defined by their population growth rate (PGR). The aim of this study is to analyse the effect of rabbit abundance on the PGR. This has been done by creating general linear models to explain autumn and spring PGR with the use of rabbit abundance estimates, enclosure size, aerial predation and previous PGR as possible explanatory variables. Rabbit abundance and enclosure size negatively affected the autumn PGR, while only rabbit abundance affected the spring PGR in the best-fit models. It is suggested that maintaining rabbit densities at fewer than 30 rabbits per hectare might help to optimise the efficiency inside enclosures.

The role of cover crop and hedges in intensive olive orchards: Preventing soil erosion and promoting biodiversity

Abstract: Trabajo presentado en el ELS 2014 Conference ("The Earth Living Skin: Soil, Life and Climate Changes", celebrada en Castellaneta (Italia) del 22 al 25 de septiembre de 2014.