Culemborg, Netherlands
Culemborg, Netherlands

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Bleeker K.,Wageningen University | Bleeker K.,University of Agder | De Jong K.,University of Cologne | Van Kessel N.,Bureau Waardenburg Bv | And 3 more authors.
PLoS ONE | Year: 2017

Alternative reproductive tactics are characterized by the occurrence of discrete alternative morphs that differ in behavioural, morphological and physiological traits within the same sex. Although much effort has been made to describe the behaviour, morphology and physiology of such alternative morphs, less effort has been invested investigating how much overlap there is in the characteristics of such morphs in natural populations. We studied random population samples of the invasive Round Goby Neogobius melanostomus from five different localities in the river Rhine system in the Netherlands. We found two morphologically and physiologically distinct male morphs which likely represent alternative reproductive tactics. Almost all mature males under 9.35 cm total length had a gonadosomatic index > 3%, suggestive of a sneaker tactic, while nearly all males above 9.35 cm has a gonadosomatic index of < 3%, suggestive of a parental tactic. Cheek size and eye diameter alone were sufficient to distinguish the two morphs. Gonads had a different relationship with size in the two morphs, indicating separate growth trajectories. The gonad mass of sneaker morphs would be ca. 7.5 times as high as the gonad mass of parental morphs of the same total length after extrapolation. Few (9%) intermediates were found, suggesting that the expression of alternative reproductive tactics is determined before the first breeding season. This contrasts with studies on other goby species, which show evidence of plastic tactics that can be affected by social circumstances. We conclude that it is possible to distinguish two alternative male morphs in the Dutch Round Goby population using morphological measurements alone. Although behavioural observations are needed to provide conclusive evidence, the difference in GSI between these morphs indicates that these morphs reflect alternative reproductive tactics. © 2017 Bleeker et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Lensink R.,Bureau Waardenburg BV | De Jong J.W.,Bureau Waardenburg BV | Kleyheeg-Hartman J.C.,Bureau Waardenburg BV
Limosa | Year: 2015

This paper describes the use of aerial photographs as a novel technique for surveying gulls breeding and resting on roofs in a large city, The Hague in the west of the Netherlands. The survey, conducted in 2010, was commissioned by the city as a basis for (evaluation of) a policy to reduce nuisance perceived by citizens due to increasing numbers of breeding gulls. The aerial photographs were taken with a laptop-operated camera mounted under a small airplane, that flew parallel transects over the city at an altitude of c. 2000 feet (Fig. 2). A first set of flights in late April yielded few breeding gulls but showed that a resolution of 3×3 cm on the ground was needed to distinguish gulls and gull nests. A second set was flown during the egg stage at the end of May, with a further flight in early June to fill in gaps between the transects of photos that arose through displacement and movements of the airplane due to wind and turbulence. Based on the coordinates of each picture, pictures were stitched together digitally to strips, which were scanned visually for breeding, resting and flying gulls. Nests were identified on the basis of behaviour of the gulls (pairs) and colour of the nest site. 422 pairs of breeding gulls were located; 30% Lesser Blackbacked Gull Larus fuscus and 70% Herring Gull L argentatus. More than 95% of ail nests were found on flat roofs with gravel. Breeding was concentrated in some parts of the city. After correction for the 39% of the area not photographed, the estimate for the entire city is 603 pairs (Tab. 2), but up to 20% of pairs may have been missed on the photographs, due to structures obstructing the view, shading, or blurring of pictures. We thus estimate that 600-720 breeding pairs were present in the city, as well as 4000-5000 non-breeding individuals of both species combined. There was only a weak positive relationship between the estimated number of breeding pairs in different city districts and the number of gulls seen resting there (Tab. 3), whereas the latter was strongly correlated with the number of flying gulls (Tab. 4, Fig. 4). Between 2000 and 2010 the number of breeding gulls in The Hague had increased by >20% yearly. These figures contrast with the national trends, a decrease in Herring Gull since the 1980s and a stabilisation in Lesser Black-backed Gull. Roof breeding may increase due to high breeding success, caused by a scarcity of predators and a wide spacing of nests which probably limits intraspecific predation.

Parmentier I.,Free University of Colombia | Harrigan R.J.,University of California at Los Angeles | Buermann W.,University of California at Los Angeles | Mitchard E.T.A.,University of Edinburgh | And 35 more authors.
Journal of Biogeography | Year: 2011

Aim Our aim was to evaluate the extent to which we can predict and map tree alpha diversity across broad spatial scales either by using climate and remote sensing data or by exploiting spatial autocorrelation patterns. Location Tropical rain forest, West Africa and Atlantic Central Africa. Methods Alpha diversity estimates were compiled for trees with diameter at breast height ≥10cm in 573 inventory plots. Linear regression (ordinary least squares, OLS) and random forest (RF) statistical techniques were used to project alpha diversity estimates at unsampled locations using climate data and remote sensing data [Moderate Resolution Imaging Spectroradiometer (MODIS), normalized difference vegetation index (NDVI), Quick Scatterometer (QSCAT), tree cover, elevation]. The prediction reliabilities of OLS and RF models were evaluated using a novel approach and compared to that of a kriging model based on geographic location alone. Results The predictive power of the kriging model was comparable to that of OLS and RF models based on climatic and remote sensing data. The three models provided congruent predictions of alpha diversity in well-sampled areas but not in poorly inventoried locations. The reliability of the predictions of all three models declined markedly with distance from points with inventory data, becoming very low at distances >50km. According to inventory data, Atlantic Central African forests display a higher mean alpha diversity than do West African forests. Main conclusions The lower tree alpha diversity in West Africa than in Atlantic Central Africa may reflect a richer regional species pool in the latter. Our results emphasize and illustrate the need to test model predictions in a spatially explicit manner. Good OLS or RF model predictions from inventory data at short distance largely result from the strong spatial autocorrelation displayed by both the alpha diversity and the predictive variables rather than necessarily from causal relationships. Our results suggest that alpha diversity is driven by history rather than by the contemporary environment. Given the low predictive power of models, we call for a major effort to broaden the geographical extent and intensity of forest assessments to expand our knowledge of African rain forest diversity. © 2011 Blackwell Publishing Ltd.

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.

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 | Lloyd J.,University of Leeds | Lloyd J.,James Cook University | Lewis S.L.,University of Leeds | And 90 more authors.
Biogeosciences | Year: 2012

Aboveground tropical tree biomass and carbon storage estimates commonly ignore tree height (H). We estimate the effect of incorporating H on tropics-wide forest biomass estimates in 327 plots across four continents using 42 656 H and diameter measurements and harvested trees from 20 sites to answer the following questions: ; 1. What is the best H-model form and geographic unit to include in biomass models to minimise site-level uncertainty in estimates of destructive biomass? ; 2. To what extent does including H estimates derived in (1) reduce uncertainty in biomass estimates across all 327 plots? ; 3. What effect does accounting for H have on plot- and continental-scale forest biomass estimates? ; The mean relative error in biomass estimates of destructively harvested trees when including H (mean 0.06), was half that when excluding H (mean 0.13). Power- and Weibull-H models provided the greatest reduction in uncertainty, with regional Weibull-H models preferred because they reduce uncertainty in smaller-diameter classes (≤40 cm D) that store about one-third of biomass per hectare in most forests. Propagating the relationships from destructively harvested tree biomass to each of the 327 plots from across the tropics shows that including H reduces errors from 41.8 Mg ha-1 (range 6.6 to 112.4) to 8.0 Mg ha-1 (-2.5 to 23.0). For all plots, aboveground live biomass was -52.2 Mg ha-1 (-82.0 to -20.3 bootstrapped 95% CI), or 13%, lower when including H estimates, with the greatest relative reductions in estimated biomass in forests of the Brazilian Shield, east Africa, and Australia, and relatively little change in the Guiana Shield, central Africa and southeast Asia. Appreciably different stand structure was observed among regions across the tropical continents, with some storing significantly more biomass in small diameter stems, which affects selection of the best height models to reduce uncertainty and biomass reductions due to H. After accounting for variation in H, total biomass per hectare is greatest in Australia, the Guiana Shield, Asia, central and east Africa, and lowest in east-central Amazonia, W. Africa, W. Amazonia, and the Brazilian Shield (descending order). Thus, if tropical forests span 1668 million km2 and store 285 Pg C (estimate including H), then applying our regional relationships implies that carbon storage is overestimated by 35 Pg C (31-39 bootstrapped 95% CI) if H is ignored, assuming that the sampled plots are an unbiased statistical representation of all tropical forest in terms of biomass and height factors. Our results show that tree H is an important allometric factor that needs to be included in future forest biomass estimates to reduce error in estimates of tropical carbon stocks and emissions due to deforestation. © 2012 Author(s).

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).

PubMed | National University of Colombia, Brown University, Manchester Metropolitan University, Instituto Federal do Espirito Santo and 110 more.
Type: Journal Article | Journal: Proceedings of the National Academy of Sciences of the United States of America | Year: 2015

The high species richness of tropical forests has long been recognized, yet there remains substantial uncertainty regarding the actual number of tropical tree species. Using a pantropical tree inventory database from closed canopy forests, consisting of 657,630 trees belonging to 11,371 species, we use a fitted value of Fishers alpha and an approximate pantropical stem total to estimate the minimum number of tropical forest tree species to fall between 40,000 and 53,000, i.e., at the high end of previous estimates. Contrary to common assumption, the Indo-Pacific region was found to be as species-rich as the Neotropics, with both regions having a minimum of 19,000-25,000 tree species. Continental Africa is relatively depauperate with a minimum of 4,500-6,000 tree species. Very few species are shared among the African, American, and the Indo-Pacific regions. We provide a methodological framework for estimating species richness in trees that may help refine species richness estimates of tree-dependent taxa.

Slik J.W.F.,CAS Xishuangbanna Tropical Botanical Garden | Paoli G.,Daemeter Consulting | Mcguire K.,Barnard College | Barroso J.,Federal University of Acre | And 58 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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