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Culemborg, Netherlands

van Kessel N.,Natuurbalans Limes Divergens BV | van Kessel N.,Radboud University Nijmegen | van Kessel N.,Bureau Waardenburg BV | Dorenbosch M.,Natuurbalans Limes Divergens BV | And 5 more authors.
Aquatic Invasions | Year: 2016

Invasions by alien species may cause a decline in populations of vulnerable protected species through interference and resource competition. During the last decade, four invasive goby species of Ponto-Caspian origin have displayed rapid dispersal in The Netherlands. High densities of these species have been recorded in large rivers and hydrologically connected water bodies such as canals and floodplain lakes. In the River Meuse, alien tubenose goby (Proterorhinus semilunaris), round goby (Neogobius melanostomus) and bighead goby (Ponticola kessleri) occupy similar habitat to native, protected river bullhead (Cottus perifretum), i.e., coarse substrates with large pebbles, and groyne stones and riprap that protect river banks against erosion and preserve river channels. In the years following the arrival in 2011 of N. melanostomus in the River Meuse, a rapid decline in native C. perifretum average density from twenty to one individual per 100 m2 was observed, most likely due to predation and competition for shelter and/or food. C. perifretum density also declined at sites colonized by Ponticola kessleri and/or Proterorhinus semilunaris only. However, when compared to sites where N. melanostomus was present, C. perifretum density remained relatively high. Similar effects on other native benthic fish species may occur in the near future due to the presence of alien gobies. Compliance with ecological status objectives relating to the European Habitats Directive and Water Framework Directive may not be achievable due to the loss of protected and endangered native fish species in areas invaded by alien gobies. © 2016 The Author(s).

de Gelder S.,National Institute of Nutrition And Seafood Research | van der Velde G.,Radboud University Nijmegen | Platvoet D.,Office Plancius | Leung N.,Radboud University Nijmegen | And 3 more authors.
Basic and Applied Ecology | Year: 2016

Invasions of alien gammarid species have led to reduced abundance of many native gammarid species and earlier gammarid invaders. Intra-guild predation (IGP) has been suggested as the main mechanism causing such species displacements. This study elucidates a mechanism for species displacement that is based on competition for shelter, viz. species excluding each other from a shelter place. Preferences of Dikerogammarus villosus and Gammarus roeselii for shelter space were studied in laboratory experiments. In contrast with night conditions both species showed a strong preference for shelter sites under daytime conditions so that all experiments were carried out under permanent light conditions. Single individuals of D. villosus sheltered more than those of G. roeselii. Intraspecific competition experiments with different size classes and sexes showed that in contrast with D. villosus, the size class had a significant effect on the mean sheltering proportion of individuals of G. roeselii. When both species were brought together in a basin with a shelter site to test interspecific competition, individuals of G. roeselii were actively pushed out of their shelters within 24. h, while D. villosus showed no change in shelter. This led to a significantly increased predation risk for G. roeselii, which was confirmed in an experiment in which a benthic fish was added. IGP only manifested itself after 48. h, indicating that competition for shelter preceded IGP. When shelter opportunities are in short supply, shelter exclusion may be one of the initial mechanisms for gammarid species displacements. Invasionen von neobiotischen Gammariden haben zu einer Reduzierung der Artenvielfalt von einheimischen und früher eingewanderten Gammariden geführt. Bisher wurde Gildeninterne Prädation (intra-guild predation, IGP) als Hauptursache für diese Artenverschiebung genannt. Diese Studie beschreibt einen anderen Mechanismus für Artenverschiebung, der auf Konkurrenz um Lebensräume basiert, wobei verschiedene Arten einander an der Nutzung von Unterschlüpfen hindern. In Laborexperimenten wurden die Präferenzen für Unterschlüpfe von Dikerogammarus villosus und Gammarus roeselii untersucht. Beide Arten bevorzugten Unterschlüpfe bei Tagesbedingungen, weswegen alle Experimente unter Dauerlichtverhältnissen durchgeführt wurden. Einzelne D. villosus-Individuen suchten mehr Schutz als G. roeselii-Individuen. Intraspezifische Konkurrenzexperimente mit verschiedenen Größenklassen und Geschlechtern zeigten, dass, im Gegensatz zu D. villosus, die Größenklasse einen signifikanten Einfluss auf den durchschnittlichen Anteil der G. roeselii-Individuen, die Schutz suchten, hatte. Um die Konkurrenz zwischen verschiedenen Arten zu testen wurden beide Arten zusammen in einem Becken gehalten. G. roeselii-Individuen wurden innerhalb von 24 Stunden aktiv aus ihren Unterschlüpfen verscheucht, während D. villosus keine Unterschiede zeigte. Dies führte zu einem signifikant erhöhten Prädationsrisiko für G. roeselii, welches in einem Experiment unter Anwesenheit einer benthische Fischart bestätigt wurde. Gildeninterne Prädation (IGP) trat erst nach 48 Stunden auf, was darauf hinweist, dass der Wettbewerb um Unterschlüpfe vor IGP stattfindet. Wenn nur wenige Unterschlüpfe vorhanden sind, kann die Verdrängung aus diesen Schutzorten einer der Mechanismen für Artenverschiebungen bei Gammariden sein. © 2016 Gesellschaft für Ökologie.

Feldpausch T.R.,University of Leeds | Banin L.,University of Leeds | Phillips O.L.,University of Leeds | Baker T.R.,University of Leeds | And 59 more authors.
Biogeosciences | Year: 2011

Tropical tree height-diameter (H:D) relationships may vary by forest type and region making large-scale estimates of above-ground biomass subject to bias if they ignore these differences in stem allometry. We have therefore developed a new global tropical forest database consisting of 39 955 concurrent H and D measurements encompassing 283 sites in 22 tropical countries. Utilising this database, our objectives were:

1. to determine if H:D relationships differ by geographic region and forest type (wet to dry forests, including zones of tension where forest and savanna overlap).

2. to ascertain if the H:D relationship is modulated by climate and/or forest structural characteristics (e.g. stand-level basal area, A).

3. to develop H:D allometric equations and evaluate biases to reduce error in future local-to-global estimates of tropical forest biomass.

Annual precipitation coefficient of variation (PV), dry season length (SD), and mean annual air temperature (TA) emerged as key drivers of variation in H:D relationships at the pantropical and region scales. Vegetation structure also played a role with trees in forests of a high A being, on average, taller at any given D. After the effects of environment and forest structure are taken into account, two main regional groups can be identified. Forests in Asia, Africa and the Guyana Shield all have, on average, similar H:D relationships, but with trees in the forests of much of the Amazon Basin and tropical Australia typically being shorter at any given D than their counterparts elsewhere. The region-environment-structure model with the lowest Akaike's information criterion and lowest deviation estimated stand-level H across all plots to within amedian −2.7 to 0.9% of the true value. Some of the plot-to-plot variability in H:D relationships not accounted for by this model could be attributed to variations in soil physical conditions. Other things being equal, trees tend to be more slender in the absence of soil physical constraints, especially at smaller D. Pantropical and continental-level models provided less robust estimates of H, especially when the roles of climate and stand structure in modulating H:D allometry were not simultaneously taken into account. © 2011 Author(s).

Lewis S.L.,University College London | Lewis S.L.,University of Leeds | Sonke B.,University of Yaounde I | Sunderland T.,Center for International Forestry Research | And 78 more authors.
Philosophical Transactions of the Royal Society B: Biological Sciences | Year: 2013

We report above-ground biomass (AGB), basal area, stemdensity and wood mass density estimates from 260 sample plots (mean size: 1.2 ha) in intact closed-canopy tropical forests across 12 African countries. Mean AGB is 395.7 Mg dry mass ha-1 (95% CI: 14.3), substantially higher than Amazonian values, with the Congo Basin and contiguous forest region attaining AGB values (429 Mg ha-1) similar to those of Bornean forests, and significantly greater than East or West African forests. AGB therefore appears generally higher in palaeo- comparedwithneotropical forests.However, mean stem density is low(426±11 stems ha-1 greater than or equal to 100 mm diameter) compared with both Amazonian and Bornean forests (cf. approx. 600) and is the signature structural feature of African tropical forests. While spatial autocorrelation complicates analyses, AGB shows a positive relationship with rainfall in the driest nine months of the year, and an opposite association with the wettest three months of the year; a negative relationship with temperature; positive relationship with clay-rich soils; and negative relationshipswith C:Nratio (suggesting a positive soil phosphorus- AGB relationship), and soil fertility computed as the sum of base cations. The results indicate that AGB is mediated by both climate and soils, and suggest that the AGB of African closed-canopy tropical forests may be particularly sensitive to future precipitation and temperature changes. © 2013 The Authors.

Slik J.W.F.,CAS Xishuangbanna Tropical Botanical Garden | Paoli G.,Daemeter Consulting | Mcguire K.,Barnard College | Amaral I.,A+ Network | And 63 more authors.
Global Ecology and Biogeography | Year: 2013

Aim: Large trees (d.b.h.≥70cm) store large amounts of biomass. Several studies suggest that large trees may be vulnerable to changing climate, potentially leading to declining forest biomass storage. Here we determine the importance of large trees for tropical forest biomass storage and explore which intrinsic (species trait) and extrinsic (environment) variables are associated with the density of large trees and forest biomass at continental and pan-tropical scales. Location: Pan-tropical. Methods: Aboveground biomass (AGB) was calculated for 120 intact lowland moist forest locations. Linear regression was used to calculate variation in AGB explained by the density of large trees. Akaike information criterion weights (AICc-wi) were used to calculate averaged correlation coefficients for all possible multiple regression models between AGB/density of large trees and environmental and species trait variables correcting for spatial autocorrelation. Results: Density of large trees explained c. 70% of the variation in pan-tropical AGB and was also responsible for significantly lower AGB in Neotropical [287.8 (mean)±105.0 (SD) Mg ha-1] versus Palaeotropical forests (Africa 418.3±91.8 Mg ha-1; Asia 393.3±109.3 Mg ha-1). Pan-tropical variation in density of large trees and AGB was associated with soil coarseness (negative), soil fertility (positive), community wood density (positive) and dominance of wind dispersed species (positive), temperature in the coldest month (negative), temperature in the warmest month (negative) and rainfall in the wettest month (positive), but results were not always consistent among continents. Main conclusions: Density of large trees and AGB were significantly associated with climatic variables, indicating that climate change will affect tropical forest biomass storage. Species trait composition will interact with these future biomass changes as they are also affected by a warmer climate. Given the importance of large trees for variation in AGB across the tropics, and their sensitivity to climate change, we emphasize the need for in-depth analyses of the community dynamics of large trees. © 2013 John Wiley & Sons Ltd.

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