Jaap van der Meer

Physiologically Inspired Regression Models for Estimating and Predicting Nutrient Stores and Their Composition in Birds

Regression models are presented that can be helpful in estimating and predicting the amount and fat and lean composition of nutrient stores in birds, when carcass data on body mass, fat mass, and body size are available. It is assumed that birds will show a breakpoint in composition during starvation, because stores, the nutrients accumulated in anticipation of shortage, have a different composition from that of the structural part of the body. The models differ only in the assumptions on the sources of variation in the data. One model, for example, assumes that all variation is due to unexplained variation in the mass of the structural part of the body. Another model assumes that the only variation is in the composition of the stores. It is shown that these models may yield completely different results. Examples suggest that the most reliable assumption on the source of variation differs among bird species. The need for ancillary information to verify the assumptions is emphasized. Prevailing methods, such as regressing fat mass on body mass and size, or regressing fat mass on condition indices such as body mass divided by size, are shown to be based on questionable assumptions, or to lack any theoretical justification, respectively. Their use should be abandoned.

Facilitation on an intertidal mudflat : the effect of siphon nipping by flatfish on burying depth of the bivalve Macoma balthica

During deposit feeding on benthic micro-algae, the siphon of buried tellinid bivalves like Macoma balthica is vulnerable to nipping by plaice Pleuronectes platessa and other flatfish. We experimentally tested the hypothesis that siphon nippers facilitate predation on the entire bivalve (by shorebirds, for example) by inducing a decrease in burying depth. Three experiments in May and in September, during which likely siphon nippers (juvenile plaice P. platessa) were allowed to feed on M. balthica siphons, demonstrated that the bivalves indeed lost siphon mass and came closer to the surface. However, the strength of the burying response and the speed of recovery of siphons after nipping varied greatly between experiments, partly as a consequence of body condition-related differences in initial burying depth. Our experimental study confirms that siphon nippers can enhance the availability of bivalve prey to probing predators, and will thus facilitate avian predation on intertidal flats.

Dredging for edible cockles (Cerastoderma edule) on intertidal flats : short-term consequences of fisher patch-choice decisions for target and non-target benthic fauna

Intertidal flats in the Dutch Wadden Sea are protected by national and international treaties. Still, mechanical dredging for edible cockles Cerastoderma edule was allowed in 74% of 1200 km(2) of interticlal flats. Cumulatively, between 1992 and 2001, 19% of the intertidal area was affected by mechanical cockle-dredging at least once. On the basis of a grid of 2650 stations sampled annually, we evaluate the extent to which cockle-dredging from 1998 to 2003 was selective with respect to non-target macrozoobenthic intertidal fauna. In all 4 years that comparisons could be made, to-be-dredged areas contained greater diversity of macrobenthic animals than areas that remained undredged. Targeted cockles were 2.5 times more abundant in areas that were to be dredged shortly, but other species also occurred in higher densities in these areas. Small amphipods and some bivalves occurred less in to-be-dredged areas than elsewhere. In terms of short-term responses to dredging, four non-target species showed a significant decrease in abundance 1 year after dredging. Only Tellina tenuis showed an increase a year after dredging.

Sampling design of monitoring programmes for marine benthos : a comparison between the use of fixed versus randomly selected stations

Abstract Three possible sampling designs for monitoring programmes were compared for both bias and variance of the associated estimators of year-to-year change. The statistical power of the accompanying univariate analysis of variance models was also analysed. The analysis was based on species abundance data from monitoring programmes for soft-bottom marine benthos in The Netherlands. The first design, with random selection of stations in each year, revealed larger variance and smaller power than the second design, in which stations are sampled randomly in the first year and revisited in succeeding years. The third design, with fixed non-randomly selected stations, yielded the largest power, but gives biased estimates of the year-to-year changes. These results suggest the following rule-of-thumb for monitoring programmes focusing on the abundance of marine benthic species: revisit many randomly selected stations, and make little effort per station.

Conservation Physiology of Marine Fishes: State of the Art and Prospects for Policy

The state of the art of research on the environmental physiology of marine fishes is reviewed from the perspective of how it can contribute to conservation of biodiversity and fishery resources. A major constraint to application of physiological knowledge for conservation of marine fishes is the limited knowledge base; international collaboration is needed to study the environmental physiology of a wider range of species. Multifactorial field and laboratory studies on biomarkers hold promise to relate ecophysiology directly to habitat quality and population status. The ‘Fry paradigm’ could have broad applications for conservation physiology research if it provides a universal mechanism to link physiological function with ecological performance and population dynamics of fishes, through effects of abiotic conditions on aerobic metabolic scope. The available data indicate, however, that the paradigm is not universal, so further research is required on a wide diversity of species. Fish physiologists should interact closely with researchers developing ecological models, in order to investigate how integrating physiological information improves confidence in projecting effects of global change; for example, with mechanistic models that define habitat suitability based upon potential for aerobic scope or outputs of a dynamic energy budget. One major challenge to upscaling from physiology of individuals to the level of species and communities is incorporating intraspecific variation, which could be a crucial component of species’ resilience to global change. Understanding what fishes do in the wild is also a challenge, but techniques of biotelemetry and biologging are providing novel information towards effective conservation. Overall, fish physiologists must strive to render research outputs more applicable to management and decision-making. There are various potential avenues for information flow, in the shorter term directly through biomarker studies and in the longer term by collaborating with modellers and fishery biologists.

Statistical analysis of the dichotomous preference test

Abstract This paper presents a general framework of statistical models for the analysis of the dichotomous preference test. It links the different approaches followed so far by students of animal feeding behaviour. A cardinal rank model, originating in econometry, is additionally placed in the same framework. This model proves to be a useful alternative when simpler models that are inspired by foraging theories fail. It is shown that the current approaches can lead to erroneous conclusions. An experimental test of the prefenence of guillemots, Uria aalge, for different size classes of sprats, Sprattus sprattus, illustrates the proposed model selection procedure.

Sorption of polychlorinated biphenyls by north sea sediments

Abstract The sediment-water partition coefficients ( K d ) of 32 polychlorinated biphenyls (PCBs) and penta- and hexachloro benzene were determined for 37 spiked sediment samples from the southern North Sea, the German Bight and the Norwegian Channel. Organic-carbon contents for these sediments were in the range 0.02–2.4%. Log( K d ) values were in the range 1.4 to 5.3. The largest difference between the organic-carbon normalised partition coefficients ( K oc ) for individual components amounted to a factor of 10. K oc values for coarse sediments were generally lower than values for fine sediments. The solids concentration effect was evaluated using the Non-Settling Particles model, the Solute Complexation model, the Implicit Adsorbate model, and the Particle Interaction model. The latter three models could be rejected on the basis of the experimental evidence. The validity of ordinary least-squares regression for estimating slope and intercept of log( K oc )-log( KK ow ) relations is discussed. Differences in sediment characteristics cause changes in the intercept of log( K oc )-log( K ow ) relations, but not in the slope. KK oc values of PCB isomers are inversely related to the number of chlorine atoms in the ortho position relative to the inter-ring bond. The validity of the data for estimating field values of sorption coefficients is discussed.

Intertidal fish traps as a tool to study long-term trends in juvenile flatfish populations☆

Abstract The suitability of intertidal fish traps (fykes, komfykes and koms) to study long-term trends in juvenile flatfish (plaice, flounder, dab and sole) was analysed with respect to effects of location, type of trap and fishing duration. For all species, catches by the three different types of fykes and on the three locations studied differed considerably, but the patterns over time were approximately the same. The results further suggest that komfykes have the highest catches of flatfish and koms the lowest. The similarity in fluctuations of catches between fish traps and between locations suggest that they may be suitable for the study of long-term changes in flatfish populations. For all species, increasing fishing duration from 24 to even up to 96 h hardly resulted in higher catches.

Indirect effects of invasive species affecting the population structure of an ecosystem engineer

Species invasion is of increasing concern as non-native species often have negative impacts on ecosystems that they were introduced to. Invaders negatively affect the abundance of native species due to direct interactions like predation and competition. Additionally, invaders may benefit native biota by imposing indirect effects on resident species interactions. Invaders indirectly affect resident species via both density-mediated indirect interactions (DMIIs) and trait-mediated indirect interactions (TMIIs). Previous studies on these different indirect interactions have largely examined the effects on structuring ecological systems, with paying little attention to the role of body size. Here, we experimentally demonstrate that an invasive habitat modifier of European coastal waters, the Pacific oyster (Crassostrea gigas), alters the population structure of native mussels (Mytilus edulis) by modifying the size specific predator-prey interaction between the mussels and the shore crab (Carcinus maenas). In laboratory split-plot experiments, the presence of Pacific oysters reduced the mortality of unconditioned mussels as well as mussels that were acclimatized in presence of predatory cues, while being exposed to predation by crabs of two different size classes. The reduction in mortality was size-dependent both in terms of the predators and the prey. The presence of oysters notably reduced mussel mortality in presence of small crabs, while the mortality rate in presence of big crabs was less affected. Mussels that benefited the most by the presence of oysters were those of recruitment stages, smaller than 20 mm in shell length. Our results suggest that oysters cause a strong shift in the population structure of M. edulis, reducing particularly the mortality of smaller sized mussels.

Mapping species abundance by a spatial zero-inflated Poisson model: a case study in the Wadden Sea, the Netherlands.

Abstract The objective of the study was to provide a general procedure for mapping species abundance when data are zero‐inflated and spatially correlated counts. The bivalve species Macoma balthica was observed on a 500×500 m grid in the Dutch part of the Wadden Sea. In total, 66% of the 3451 counts were zeros. A zero‐inflated Poisson mixture model was used to relate counts to environmental covariates. Two models were considered, one with relatively fewer covariates (model “small”) than the other (model “large”). The models contained two processes: a Bernoulli (species prevalence) and a Poisson (species intensity, when the Bernoulli process predicts presence). The model was used to make predictions for sites where only environmental data are available. Predicted prevalences and intensities show that the model “small” predicts lower mean prevalence and higher mean intensity, than the model “large”. Yet, the product of prevalence and intensity, which might be called the unconditional intensity, is very similar. Cross‐validation showed that the model “small” performed slightly better, but the difference was small. The proposed methodology might be generally applicable, but is computer intensive.