Peter Hobbelen
Post-Doctoral Research Associate
Department of Forest and Wildlife Ecology
University of Wisconsin-Madison
Contact information:
218 Russell Laboratory
1630 Linden Drive
Madison, WI 53706
phone: +1-608-263-7595
fax: +1-608--262-6099
email: hobbelen@wisc.edu
Education:
2001-2005 PhD-ecotoxicology. Department of Animal Ecology, Vrije Universiteit Amsterdam, the Netherlands.
1995-2000. MSc-theoretical and population biology. Wageningen University and Research Centre (WUR), Wageningen, the Netherlands.
Research interests:
I am very interested in the development of mathematical models that integrate data to understand and predict the dynamics of populations and communities of organisms and how these depend on biotic and abiotic factors like infectious diseases, climate change and pollution. I am also very interested in the relation between the structure and functioning of ecosystems.
Current Postdoctoral research (Oct 2007-Jan 2008)
context
Endemic Hawaiian honeycreepers (Drepanidinae) face one of the highest extinction rates in the world. The introduction of avian malaria (Plasmodium relictum) and its vector, the Southern House mosquito (Culex quinquefasciatus), are considered to be the primary factors contributing to population declines and changes in the geographic and altitudinal distribution of these birds.
Tropical Montane Cloud Forests are an important habitat for Hawaiian honeycreepers and occur up to approximately 2000 m altitude on the island of Hawaii. The parts of the forest that are located at higher elevations form a disease free refuge for the Hawaiian honeycreepers due to the prevailing low temperatures that prevent the colonization by mosquitoes and the transmission of avian malaria. In areas that are suitable for colonization by mosquitoes, malaria transmission is seasonal at mid-elevations and year-round at low elevations.
A possible management strategy to reduce the transmission of avian malaria to birds is the reduction of mosquito populations. The Southern House mosquito breeds in cavities in the forest and in rock pools in streambeds. The cavities in the forest are created by introduced feral pigs (Sus scrofa). Pig removal is therefore a promising strategy to reduce mosquito populations and therefore the transmission of avian malaria to Hawaiian honeycreepers. Another possible management strategy involves the translocation of Hawaiian honey creepers from certain populations at low elevations that developed resistance against the disease to other areas. Computer modeling can help to determine the efficacy and efficiency of these management strategies.
research aims
The aims of this study were to determine the effects of pig removal and translocation of disease-resistant individuals of endemic Hawaiian honey creepers on the transmission of avian malaria to endemic Hawaiian honey creepers and the resulting consequences for their population dynamics.
methods
An existing continuous time model consisting of ordinary differential equations will be further developed and expanded with gamma distributed sojourn times in developmental and infectious stages. The model includes one vector and 4 host species and distinguishes between juvenile and adult stages, subdivided into different disease stages.
Previous Postdoctoral research (Oct 2005 – Sep 2007)
context
This research is closely linked to my current research project (described above) and assessed the impact of a native biological predator, the beautiful Hawaiian damselfly (Megalagrion calliphya), on the population dynamics of the Southern House mosquito (Culex quinquefasciatus) an important vector of avian malaria. Instead of my current research project, which focuses on the control of mosquito populations that breed in cavities in forests, this project focused on mosquitoes that breed in rock pools in stream beds that are occupied by both M. calliphya and C. quinquefasciatus larvae. Temperature is an important driver of the population dynamics of poikilothermic predator-prey systems and therefore it was expected that the ability of M. calliphya to control C. quinquefasciatus populations would change along an altitudinal gradient in the Tropical Montane Cloud Forest on the island of Hawaii and could also be affected by global warming.
research aims
The objectives of this study were to determine the impact of the predation of C. quinquefasciatus larvae by M. calliphya larvae on the population dynamics of adult C. quinquefasciatus along an altitudinal gradient in Hawaii for the current climate and with predicted global warming.
methods
Continuous time population models for M. calliphya and C. quinquefasciatus consisting of delay differential equations with variable time delays were developed to address the research questions.
PhD project (Mar 2001-Feb 2005)
context
Although the levels of pollutants in European rivers decreased due to environmental policy by governments, most floodplain soils of these rivers are still highly polluted, due to the binding of polluted particles to the soil matrix. This led to concern about possible effects of these pollutants on soil dwelling organisms that play an important role in the cycling of elements in ecosystems.
research aims
The aim of my PhD-project was to determine the bioavailability of heavy metals in polluted floodplain soils and the effects of bioavailable metal concentrations on the structure and functioning of detritivore communities (earthworms, isopods and millipedes).
methods
I used a combination of field and laboratory experiments and mathematical modelling to answer the research aims.
Field experiments: The field work started with a pilot-experiment in order to determine important detritivore groups and heavy metal species that potentially affected the functioning of these groups. Next, a large field experiment was started using 15 field sites that constituted a gradient in heavy metal pollution. Aim of this field experiment was to determine which metal pools were important for the uptake of heavy metals in detritivores and to determine the influence of metal pollution on the structure and functioning of the detritivore community. The structure of the detritivore community was determined by collecting data on species richness, species densities and biomass. The functioning of the detritivore community was determined using different indicators of litter decomposition. Correlation tests and linear regression were used to determine metal pools that could be important for the uptake of heavy metals by detritivores. Multivariate analysis (PCA, RDA) was used to study relations between metal pollution and the structure and functioning of the detritivore community
Lab experiments: results from the field experiments showed that, in specific, one earthworm species (Lumbricus rubellus) influenced the decomposition of litter. Therefore, a bioassay was set up to determine the effects of heavy metals on the litter consumption of this species and to determine the possibility of long-term exposed earthworms being adapted to heavy metal pollution.
Modelling study: in order to determine the validity of extrapolating results of the bioassay mentioned above to field conditions, a mechanistic Dynamic Energy Budget model was used to predict the influence of different temperature and food density scenarios on the effects of Cu on the food consumption of earthworms.
MSc-projects (1998-2000)
I wrote two theses for the fulfillment of my MSc degree. The first thesis was in the field of theoretical biology and aimed to determine the influence of food density and predation on the burying depth of the bivalve Macoma balthica, using a Dynamic Energy Budget modelling approach. The second thesis was in the field of population biology and aimed to determine the influence of the type and number of overnight refuges that is used by the South Australian sleepy lizard (Tiliqua rugosa) on its tick load by conducting and analysing field experiments.
Scientific publications
1. Hobbelen, P.H.F., Samuel, M.D., Foote, D., Tango, L., La Pointe, D.A. Potential impacts of climate change on a predator-prey system: mosquitoes, damselflies and avian malaria in Hawaii. Submitted.
2. Rozema, J. Notten. M., Aerts, R., Van Gestel, K., Hobbelen, P., Hamers, T. Do high levels of diffuse and chronic metal pollution in sediments of the Rhine and Meuse floodplains affect structure and functioning of terrestrial ecosystems? Submitted.
3. Hobbelen, P.H.F., Van Gestel, C.A.M., 2007. Using dynamic energy budget modelling to predict the influence of temperature and food density on the effect of Cu on earthworm mediated litter consumption. Ecological Modelling 202, 373-384.
4. Veltman, K., Huijbregts, M.A.J., Vijver, M.G., Peijnenburg, W.J.G.M., Hobbelen, P.H.F., Koolhaas, J.E., Van Gestel, C.A.M., Van Vliet, P.C.J., Hendriks, J.A., 2007. Metal accumulation in the earthworm Lumbricus rubellus. Model predictions compared to field data. Environmental Pollution 146, 428-436.
5. Hobbelen, P.H.F., Koolhaas, J.E., Van Gestel, C.A.M., 2006. Bioaccumulation of heavy metals in the earthworms Lumbricus rubellus and Aporrectodea caliginosa in relation to total and available metal concentrations. Environmental Pollution 144, 639-646.
6. Hobbelen, P.H.F., Van den Brink, P.J., Hobbelen, J.F., Van Gestel, C.A.M., 2006. Effects of heavy metals on the structure and functioning of detritivores in a contaminated floodplain area. Soil Biology & Biochemistry 38, 1596-1607.
7. Hobbelen, P.H.F., Koolhaas, J.C. and Van Gestel, C.A.M., 2006. Effects of heavy metals on litter consumption by the earthworm Lumbricus rubellus in field soils. Pedobiologia 50, 51-60.
8. Hobbelen, P.H.F., Koolhaas, J.C. and Van Gestel, C.A.M., 2004. Risk assessment of heavy metal pollution for detritivores in floodplain soils in the Biesbosch, the Netherlands, taking bioavailability into account. Environmental Pollution 129,409-419