Large-Scale Changes in Community Composition: Determining Land Use and Climate Change Signals

Human land use and climate change are regarded as the main driving forces of present-day and future species extinction. They may potentially lead to a profound reorganisation of the composition and structure of natural communities throughout the world. However, studies that explicitly investigate both forms of impact—land use and climate change—are uncommon. Here, we quantify community change of Dutch breeding bird communities over the past 25 years using time lag analysis. We evaluate the chronological sequence of the community temperature index (CTI) which reflects community response to temperature increase (increasing CTI indicates an increase in relative abundance of more southerly species), and the temporal trend of the community specialisation index (CSI) which reflects community response to land use change (declining CSI indicates an increase of generalist species). We show that the breeding bird fauna underwent distinct directional change accompanied by significant changes both in CTI and CSI which suggests a causal connection between climate and land use change and bird community change. The assemblages of particular breeding habitats neither changed at the same speed and nor were they equally affected by climate versus land use changes. In the rapidly changing farmland community, CTI and CSI both declined slightly. In contrast, CTI increased in the more slowly changing forest and heath communities, while CSI remained stable. Coastal assemblages experienced both an increase in CTI and a decline in CSI. Wetland birds experienced the fastest community change of all breeding habitat assemblages but neither CTI nor CSI showed a significant trend. Overall, our results suggest that the interaction between climate and land use changes differs between habitats, and that comparing trends in CSI and CTI may be useful in tracking the impact of each determinant

Ensambles de aves diurnas a través de un gradiente de perturbación en un paisaje en el sureste de México

In order to assess of a Mexican tropical landscape like birds shelter, in the 2008 we evaluated richness, abundance, distribution and foraging guilds of birds in eight landscape units, nested within two ecomosaics. Of 218 species identified, 207 were recorded during dry season and 119 in the rain season. Species composition differed between the two ecomosaics, (a) heterogeneous agriculture matrix and (b) rain forest remnant, and among their nested landscape units. Shannon-Wiener index was similar (from 3.20 to 4.44) among landscape units, and mean species richness varied from 76 to 118species, while avian communities were equally distributed (Pielou: 0.71 to 0.91). At the landscape scale, the two ecomosaics play complementary roles in maintaining high bird diversity, providing habitat for high value conservation species like Tinamus major, Crypturellus soui, Crax rubra, Amazona farinosa, Odonthophorus guttatus, Chondrohierax uncinatus, Platyrinchus cancrominus, Onycorhynchus coronatus and Manacus candei. Foraging guilds frequencies differ by landscape units. For example in pasturelandswith spare trees, perch hunters and cattle-associated birds were abundant, while insectivores gleaning from soil, bark and foliage were common into the forest. Species like Lipaugus unirufus, Pipramentalis and Shiffornis turdinus could be ecological indicators of conserved forest conditions while Sporophila americana, S. torqueola, Pitangus sulphuratus, Cyanocorax morio and Crotophaga sulcirostris favor disturbed native forest habitat. Current patterns of landscape management constitute a potential model of sustainable management for both agricultural production and bird conservation. However this management model is threatened by external and internal drivers of extensive cattle ranching, the abandonment of swidden systems and gradual extraction of wood from local forests.Con el objetivo de evaluar la diversidad de aves que se presentan en un paisaje del trópico mexicano, en el año 2008 se evaluó la riqueza, abundancia y distribución de las aves y sus gremios de forrajeo en ocho unidades del paisaje agrupadas en dos ecomosaicos. De las 218 especies identificadas, 207 estuvieron presentes en la estación seca y 119 en la de lluvias. Se encontró que la composición de avifauna difiere entre los ecomosaicos (a) matriz agropecuaria heterogénea y (b) bosque tropical perennifolio,así como entre las unidades de paisaje anidadas en ellos. La riqueza varió de 76 a 118 especies entre unidades del paisaje, mientras que el índice de diversidad de Shannon-Wiener resultó similar (de 3.20 a 4.44), y las comunidades de aves se distribuyeron equitativamente (Pielou: 0.71 a 0.91). En el paisaje se configura un escenario complementario entre ecomosaicos y una diversidad de aves muy alta, incluyendo especies importantes para la conservación como Tinamus major, Crypturellus soui, Crax rubra, Amazona farinosa, Odontophorus guttatus, Chondrohierax uncinatus, Platyrinchus cancrominus, Onycorhynchus coronatus y Manacus candei. Los gremios de forrajeo de aves se separan en función de las características ambientales de las unidades de paisaje por ejemplo, en los potreros con árboles dispersos predominan cazadoras desde percha y especies asociadas al ganado, mientras que en el bosquepredominan los insectívoros que buscan sus presas en el suelo, corteza y follaje. Algunas especies como Lipaugus unirufus, Pipra mentalis y Schiffornis turdinus pueden funcionar como indicadoras ecológicas del bosque conservado, mientras otras como Sporophila americana, S. torqueola, Pitangus sulphuratus, Myozetetes similis, Cyanocorax morio y Crotophaga sulcirostris lo son para el estado perturbado del bosque nativo. El paisaje actual conformado por remanentes de bosque y una matriz agropecuaria con arbolado, posibilita la conservación biológica de aves, constituyendo un modelo potencial para su refugio y manejo sustentable. Sin embargo, la expansión de la ganadería extensiva, el abandono del sistema de rotación milpa-acahual y la extracción gradual de madera del bosque en el ejido, pone en riesgo la diversidad de la avifauna en la zona de estudio.

Love thy neighbour?-Spatial variation in density dependence of nest survival in relation to predator community

Aim: In many species, density-dependent effects on reproduction are an important driver of population dynamics. However, it is rarely considered that the direction of density dependence is expected to vary over space and time depending on anti-predator behaviour and predator community. Aggregation may allow for effective group mobbing against avian nest predators while aggregation may also attract mammalian predators, causing negative density dependence. We aim to quantify spatial variation in the effect of conspecific breeding density on nest survival in a mobbing bird species (Eurasian oystercatcher; Haematopus ostralegus) and identify whether this variation in density dependence can be explained by the predator community. Location: Country-wide (The Netherlands). Methods: We integrated reproductive data with breeding territory maps of Eurasian oystercatchers and occupancy maps of avian and mammalian predator species across the Netherlands for a 10-year period. Results: Spatial variation in the composition of the predator community explained the effects of neighbour density, showing decreasing nest survival when both conspecific density and mammalian dominance increased. Also, heterospecific density (from breeding godwits and lapwing) has an additional effect on the oystercatcher nest survival. Strikingly, this pattern did not extend to mammal-free island populations. Main conclusions: Our study provides evidence that both the strength and sign of density dependence can vary spatially within species, implying that it is dangerous to generalize results from a single local population to large-scale management implications and modelling exercises. The study also suggests that conservation actions that aim to attract breeding birds should be prioritized in areas with fewer mammalian predators, but this idea requires further testing on island populations

Interactive effects of plant species diversity and elevated CO2 on soil biota and nutrient cycling

Terrestrial ecosystems consist of mutually dependent producer and decomposer subsystems, but not much is known on how their interactions are modified by plant diversity and elevated atmospheric CO2 concentrations. Factorially manipulating grassland plant species diversity and atmospheric CO2 concentrations for five years, we tested whether high diversity or elevated CO2 sustain larger or more active soil communities, affect soil aggregation, water dynamics, or nutrient cycling, and whether plant diversity and elevated CO2 interact. Nitrogen (N) and phosphorus (P) pools, symbiotic N2 fixation, plant litter quality, soil moisture, soil physical structure, soil nematode, collembola and acari communities, soil microbial biomass and microflora community structure (phospholipid fatty acid [PLFA] profiles), soil enzyme activities, and rates of C fluxes to soils were measured. No increases in soil C fluxes or the biomass, number, or activity of soil organisms were detected at high plant diversity; soil H2O and aggregation remained unaltered. Elevated CO2 affected the ecosystem primarily by improving plant and soil water status by reducing leaf conductance, whereas changes in C cycling appeared to be of subordinate importance. Slowed-down soil drying cycles resulted in lower soil aggregation under elevated CO2. Collembola benefited from extra soil moisture under elevated CO2, whereas other faunal groups did not respond. Diversity effects and interactions with elevated CO2 may have been absent because soil responses were mainly driven by community-level processes such as rates of organic C input and water use; these drivers were not changed by plant diversity manipulations, possibly because our species diversity gradient did not extend below five species and because functional type composition remained unaltered. Our findings demonstrate that global change can affect soil aggregation, and we advocate that soil aggregation should be considered as a dynamic property that may respond to environmental changes and feed back on other ecosystem functions

Temporal trend of the community specialisation index of the entire Dutch breeding bird fauna (bold line) and for breeding bird communities in forests, farmland, dunes and coast, heath and wetland between 1984 and 2009.

<p>Temporal trend of the community specialisation index of the entire Dutch breeding bird fauna (bold line) and for breeding bird communities in forests, farmland, dunes and coast, heath and wetland between 1984 and 2009.</p