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Research Interests: Biology, Medicine, Energy Metabolism, Cell Division, Humans, and 15 moreEnergy demand, Calorie restriction, Mathematical Computing, Energy Expenditure, Mathematical Model, Neoplasm Invasiveness, Immunocompromised host, Neoplasms, Growth rate, Cachexia, Age Factors, Body Weight, Cell Proliferation, Energy Intake, and Doubling Time
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Analysis of transect counts to monitor population size in endangered insects The case of the El Segundo blue butterfly, Euphilotes bernardino allyni
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Normative data are needed to create a reference that indicates optimal development of weight in relation to height and age, particularly in the face of the unfolding obesity epidemic. The body-mass index (BMI) has some serious... more
Normative data are needed to create a reference that indicates optimal development of weight in relation to height and age, particularly in the face of the unfolding obesity epidemic. The body-mass index (BMI) has some serious limitations: it is a relatively poor predictor of current and future fatness. Currently, however, there are few available alternatives, with the possible exception of waist circumference or skinfolds. The use of cross-sectional references to construct a BMI-reference curve is problematic when there are period and cohort effects. Ideally, a reference would be based on longitudinal data in populations with little underweight, overweight, and obesity. In the meantime cross-sectional data in appropriate populations could be used to construct BMI percentiles linking BMI values at age 5 to those at age 18 (or 21) that would correspond with adult BMI values reflecting optimal health (e.g., that would correspond to adult BMI values between 21 and 23 kg/m2).
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... These either stress the importance of reduced selection for early male emergence or the impor-tance of selection for large male size. * E-mail: cor@bio.vu.nl. Am. Nat. 1996. Vol. 147, pp. 946-965. © 1996 by The University of Chicago.... more
... These either stress the importance of reduced selection for early male emergence or the impor-tance of selection for large male size. * E-mail: cor@bio.vu.nl. Am. Nat. 1996. Vol. 147, pp. 946-965. © 1996 by The University of Chicago. 0003-0147/96/4706-0004$02.00. ...
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... 0.684%). 0.132) x; (P < The difference in body mass apparently is a difference inlean body mass, which indicates a difference in growth. This also appears in Fig. 4 from the difference h by se, in final length. ith body size, es ...
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In this article, I analyse how photoadaption affects the photosynthesis-irradiance curve in phytoplankton. Four parameters are presumably affected by photoadaption: (1) the size of a photosynthetic unit; (2) the number of photosynthetic... more
In this article, I analyse how photoadaption affects the photosynthesis-irradiance curve in phytoplankton. Four parameters are presumably affected by photoadaption: (1) the size of a photosynthetic unit; (2) the number of photosynthetic units per cell; (3) the average turnover time of a photosynthetic unit; and (4) the chlorophyll-specific absorption cross-section. Prezelin&#39;s well-known conceptual model of photoadaption deals with variation in size and number of photosynthetic units, but not with the other two parameters. Prezelin&#39;s model predicts that the photosynthesis-irradiance curve is differentially affected by variations in size or number of photosynthetic units. By contrast, my analysis shows that if photoadaptional variation in the turnover time is also accounted for, only the cellular chlorophyll concentration is relevant; variation in the size vs. number of photosynthetic units is immaterial. The photoadaptional response of the chlorophyll-specific absorption cross-section allows a simple description consistent with experimental data. I use this description to derive a single expression for the rate of photosynthesis as dependent on irradiance and the cellular chlorophyll concentration. This model for the photosynthesis-irradiance-curve accounts for the photoadaptional alterations of all four parameters. Copyright 1997 Academic Press Limited
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The carbon cell quota of light-limited microalgae often increases with average photon flux density. Models of light-limited microalgal growth do not account for this phenomenon, however. In this paper we present a model of the carbon... more
The carbon cell quota of light-limited microalgae often increases with average photon flux density. Models of light-limited microalgal growth do not account for this phenomenon, however. In this paper we present a model of the carbon budget of phytoplankton, which accounts for the variation in carbon cell quota with photon flux density. We distinguish two components in the cell, permanent
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Many models of microalgal growth focus on steady state carbon budgets. This approach can be very useful if one&#39;s primary purpose is to predict growth on the basis of a limited set of measurements. However, it is less likely to be... more
Many models of microalgal growth focus on steady state carbon budgets. This approach can be very useful if one&#39;s primary purpose is to predict growth on the basis of a limited set of measurements. However, it is less likely to be successful if one purports to understand the regulation of growth in response to variations in, for instance, the nutrient
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Growth of birds is described by a variety of mathematical equations. These equations generally lack a biological motivation. As a result, it remains unclear why growth in different species should be described by different equations. In... more
Growth of birds is described by a variety of mathematical equations. These equations generally lack a biological motivation. As a result, it remains unclear why growth in different species should be described by different equations. In this article, we argue that the gradual development of endothermy affects the growth of birds. Hence, differences in the growth curve may result from differences in the thermal ontogeny. We assume that birds would grow according to the von Bertalanffy growth equation, if their temperature were constant. Using the deviations from this growth curve, we reconstruct the time course of the temperature of growing birds. This reconstruction well describes data on the ontogeny of the body temperature in birds.
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... Experimental animals Juvenile specimens of L. stagnalis (shell height 8-10 mm) bred under standard conditions (van der Sleen et al ... cooperation in the immunocytochemical experiments, to Mrs. MJM Bergamin-Sassen for technical... more
... Experimental animals Juvenile specimens of L. stagnalis (shell height 8-10 mm) bred under standard conditions (van der Sleen et al ... cooperation in the immunocytochemical experiments, to Mrs. MJM Bergamin-Sassen for technical assistance, and to Mrs. Thea Laan for typing ...
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Microalgal growth models aim to predict growth rate as well as cellular composition, given the environmental conditions (such as temperature, nutrient availability, light, etc.). This generic purpose poses strong requirements to the... more
Microalgal growth models aim to predict growth rate as well as cellular composition, given the environmental conditions (such as temperature, nutrient availability, light, etc.). This generic purpose poses strong requirements to the structure of any model attempting to comply with it. First, cellular characteristics should be modelled, rather than taken as model input. Second, if one interprets ‘cellular composition’ as
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The ratio of chlorophyll a per cell and carbon per cell is considered to be a key quantity in phytoplankton growth. The quantity varies with nutrient and light availability. The aim of this paper is to predict how the chlorophyll a to... more
The ratio of chlorophyll a per cell and carbon per cell is considered to be a key quantity in phytoplankton growth. The quantity varies with nutrient and light availability. The aim of this paper is to predict how the chlorophyll a to carbon ratio varies in relation to environmental conditions. A cell-based model is presented, that allows the description of
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Research Interests: Modeling, Multidisciplinary, Ecological Modelling, Ecosystem Modelling, Weak interaction, and 14 moreFood web, Predation, Nutrient Enrichment, Theoretical Analysis, Nutrient, Intraguild Predation, Spectrum, Ecosystem, Trophic Interaction, Guild, Food Chain, Bifurcation Analysis, Interaction Strength, and Omnivore
ABSTRACT . 1The time course of abundance of adult insects emerging in discrete generations is modelled, assuming the absence of net migration and a constant death rate. The time till emergence is assumed to be logistically... more
ABSTRACT . 1The time course of abundance of adult insects emerging in discrete generations is modelled, assuming the absence of net migration and a constant death rate. The time till emergence is assumed to be logistically distributed.2The qualitative features of the model depend on one dimensionless parameter only, namely the product of the death rate and a dispersion measure for the symmetric emergence distribution.3The model is fitted to data on the abundance of five butterfly species. The tit is excellent; moreover, the estimated death rates are well within the range given in the literature (mostly 0.1–0.2 day-1). Death rates are generally obtained by mark-recapture methods. The present model gives the opportunity to evaluate some assumptions of these methods.
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ABSTRACT Results of experiments on egg development, size-dependent feeding, growth and starvation of the pond snail Lymnaea stagnalis (L.) were successfully represented by a model for energy budgets that has already proved to be... more
ABSTRACT Results of experiments on egg development, size-dependent feeding, growth and starvation of the pond snail Lymnaea stagnalis (L.) were successfully represented by a model for energy budgets that has already proved to be applicable to other animals. We studied the interference of the budget by changing the photoperiod. This perturbation affected the model parameter representing energy allocation to reproduction plus development as opposed to representing growth plus maintenance. These results give further support to the mechanistic assumptions on which the model is based and provide a basis for modelling the extensive physiological data already available for this animal.