11 results on '"Fokkema, W."'
Search Results
2. Ontogenetic niche shifts as a driver of seasonal migration
- Author
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Fokkema, W., van der Jeugd, H.P., Lameris, T.K., Dokter, A.M., Ebbinge, B.S., de Roos, A.M., Nolet, B.A., Piersma, T., Olff, H., Fokkema, W., van der Jeugd, H.P., Lameris, T.K., Dokter, A.M., Ebbinge, B.S., de Roos, A.M., Nolet, B.A., Piersma, T., and Olff, H.
- Abstract
Ontogenetic niche shifts have helped to understand population dynamics. Here we show that ontogenetic niche shifts also offer an explanation, complementary to traditional concepts, as to why certain species show seasonal migration. We describe how demographic processes (survival, reproduction and migration) and associated ecological requirements of species may change with ontogenetic stage (juvenile, adult) and across the migratory range (breeding, non-breeding). We apply this concept to widely different species (dark-bellied brent geese (Branta b. bernicla), humpback whales (Megaptera novaeangliae) and migratory Pacific salmon (Oncorhynchus gorbuscha) to check the generality of this hypothesis. Consistent with the idea that ontogenetic niche shifts are an important driver of seasonal migration, we find that growth and survival of juvenile life stages profit most from ecological conditions that are specific to breeding areas. We suggest that matrix population modelling techniques are promising to detect the importance of the ontogenetic niche shifts in maintaining migratory strategies. As a proof of concept, we applied a first analysis to resident, partial migratory and fully migratory populations of barnacle geese (Branta leucopsis). We argue that recognition of the costs and benefits of migration, and how these vary with life stages, is important to understand and conserve migration under global environmental change.
- Published
- 2020
3. Agricultural pastures challenge the attractiveness of natural saltmarsh for a migratory goose
- Author
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Dokter, A.M., Fokkema, W., Ebbinge, B.S., Olff, Han, van der Jeugd, H.P., Nolet, B.A., Dokter, A.M., Fokkema, W., Ebbinge, B.S., Olff, Han, van der Jeugd, H.P., and Nolet, B.A.
- Abstract
Broad‐scale land conversions and fertilizer use have dramatically altered the available staging area for herbivorous long‐distance migrants. Instead of natural land, these birds rely increasingly on pastures for migratory fuelling and stopover, often conflicting with farming practices. To predict and manage birds’ future habitat use, the relative advantages and disadvantages of natural (e.g. saltmarsh, intertidal) versus anthropogenic staging sites for foraging need to be understood. We compared the migratory staging of brent geese on saltmarsh and pasture sites in spring. Food quality (nitrogen and fibre content), antagonistic behaviour, and body weight were quantified at nearby sites in simultaneous seasons. Individuals were tracked with high‐resolution GPS and accelerometers to compare timing of migration and time budgets during fuelling. On pastures, birds rested more and experienced higher ingestion rates, similar or superior food quality and reduced antagonistic interactions than on saltmarsh. Brent geese using fertilized grasslands advanced their fuelling and migration schedules compared to those using saltmarsh. Pasture birds reached heavy weights earlier, departed sooner, and arrived in the Arctic earlier. Intertidal mudflats were frequently visited by saltmarsh birds during the day, and available food there (algae, some seagrass) was of higher quality than terrestrial resources. Availability of intertidal resources was an important factor balancing the otherwise more favourable conditions on pastures relative to saltmarsh. Synthesis and applications. Disadvantages of longer foraging effort, more antagonistic interactions and delayed fuelling schedules on traditional saltmarshes may cause geese to exchange this traditional niche in favour of pastures, especially in a warming climate that requires advancement of migratory schedules. However, due to its high quality, intertidal forage can complement terrestrial foraging, potentially removi
- Published
- 2018
4. Body stores persist as fitness correlate in a long-distance migrant released from food constraints
- Author
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Dokter, A.M., Fokkema, W., Bekker, S.K., Bouten, W., Ebbinge, B.S., Müskens, G., Olff, H., van der Jeugd, H.P., Nolet, B.A., Dokter, A.M., Fokkema, W., Bekker, S.K., Bouten, W., Ebbinge, B.S., Müskens, G., Olff, H., van der Jeugd, H.P., and Nolet, B.A.
- Abstract
Long-distance migratory birds rely on the acquisition of body stores to fuel their migration and reproduction. Breeding success depends on the amount of body stores acquired prior to migration, which is thought to increase with access to food at the fueling site. Here, we studied how food abundance during fueling affected time budgets and reproductive success. In a regime of plenty, we expected that 1) limitations on food harvesting would become lifted, allowing birds to frequently idle, and 2) birds would reach sufficient fuel loads, such that departure weight would no longer affect reproductive success. Our study system comprised brent geese (Branta b. bernicla) staging on high-quality agricultural pastures. Fueling conditions were assessed by a combination of high-resolution GPS tracking, acceleration-based behavioral classification, thermoregulation modeling, and measurements of food digestibility and excretion rates. Mark-resighting analysis was used to test for correlations between departure weight and offspring recruitment. Our results confirm that birds loafed extensively, actively postponed fueling in early spring, and took frequent digestion pauses, suggesting that traditional time constraints on harvest and fueling rates are absent on modern-day fertilized grasslands. Nonetheless, departure weight remained correlated with recruitment success. The persistence of this correlation after a prolonged stopover with access to abundant highquality food, suggests that between-individual differences in departure condition are not so much enforced by food quality and availability during stopover, but reflect individual quality and longer-lived life-history traits, such as health status and digestive capacity, which may be developed before the fueling period.
- Published
- 2018
5. Mires in the Maluti Mountains of Lesotho
- Author
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Grundling, P.-L., Linström, A., Fokkema, W., Grootjans, A.P., Grundling, P.-L., Linström, A., Fokkema, W., and Grootjans, A.P.
- Abstract
Contains fulltext : 149842.pdf (publisher's version ) (Open Access)
- Published
- 2015
6. Functional traits of trees on and off termite mounds:Understanding the origin of biotically-driven heterogeneity in savannas
- Author
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van der Plas, F., Howison, R., Reinders, J., Fokkema, W., Olff, H., van der Plas, F., Howison, R., Reinders, J., Fokkema, W., and Olff, H.
- Abstract
Questions In African savannas, Macrotermes termites contribute to small-scale heterogeneity by constructing large mounds. Operating as islands of high nutrient and water availability and low fire frequency, these mounds support distinct, diverse communities of trees that have been shown to be highly attractive to browsers. However, the distinct traits of tree species on termite mounds have hardly been studied, even though this may help to understand processes determining (1) their characteristic community structure and (2) attractiveness for browsers. Here, we compare functional trait and browser preference values between tree species on and off termite mounds. Location Hluhluwe-iMfolozi Park, Kwazulu-Natal, South Africa. Methods We recorded tree community compositions for 16 large Macrotermes natalensis mounds and 16 control plots of 100 m2 each in a paired design. For each observed tree species we measured 22 traits, related to water and nutrient use, fire tolerance, light competition and anti-herbivore defence, and compared average trait values between mound and control communities. Furthermore, we investigated the feeding preferences of ungulate browsers for the most common tree species and how this was linked to their associated traits. Results Termite mounds supported tree communities that were distinct from the surrounding savanna vegetation. Mounds hosted more evergreen and less leguminous tree species than control communities, and the dominant species were less mechanically defended, less nutritious, had larger leaves and lower wood density than the species dominating control plots. Browsers preferred leguminous tree species with high leaf N and P content, which were relatively rare on termite mounds. Conclusions Overall, we conclude that termite mounds in this savanna form small refuges for tree species that seem less adapted to fire (more evergreens), have low nutrient availability (less nitrogen fixers) and suffer from water stress (larger leaf sizes)
- Published
- 2013
7. Functional traits of trees on and off termite mounds: understanding the origin of biotically-driven heterogeneity in savannas
- Author
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Van der Plas, F., primary, Howison, R., additional, Reinders, J., additional, Fokkema, W., additional, and Olff, H., additional
- Published
- 2012
- Full Text
- View/download PDF
8. Natuurontwikkeling in het Laegieskampgebied [themanummer natuurontwikkeling]
- Author
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Mars, H. de, Fokkema, W., Alphen, J. van, Mars, H. de, Fokkema, W., and Alphen, J. van
- Published
- 1995
9. Functional traits of trees on and off termite mounds: understanding the origin of biotically-driven heterogeneity in savannas.
- Author
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Plas, F., Howison, R., Reinders, J., Fokkema, W., Olff, H., and Bruun, Hans Henrik
- Subjects
INSECT societies ,SAVANNAS ,GRASSLANDS ,TERMITIDAE ,TERMITOMYCES ,MACROTERMES - Abstract
Questions In African savannas, Macrotermes termites contribute to small-scale heterogeneity by constructing large mounds. Operating as islands of high nutrient and water availability and low fire frequency, these mounds support distinct, diverse communities of trees that have been shown to be highly attractive to browsers. However, the distinct traits of tree species on termite mounds have hardly been studied, even though this may help to understand processes determining (1) their characteristic community structure and (2) attractiveness for browsers. Here, we compare functional trait and browser preference values between tree species on and off termite mounds. Location Hluhluwe-i Mfolozi Park, Kwazulu- Natal, South Africa. Methods We recorded tree community compositions for 16 large Macrotermes natalensis mounds and 16 control plots of 100 m
2 each in a paired design. For each observed tree species we measured 22 traits, related to water and nutrient use, fire tolerance, light competition and anti-herbivore defence, and compared average trait values between mound and control communities. Furthermore, we investigated the feeding preferences of ungulate browsers for the most common tree species and how this was linked to their associated traits. Results Termite mounds supported tree communities that were distinct from the surrounding savanna vegetation. Mounds hosted more evergreen and less leguminous tree species than control communities, and the dominant species were less mechanically defended, less nutritious, had larger leaves and lower wood density than the species dominating control plots. Browsers preferred leguminous tree species with high leaf N and P content, which were relatively rare on termite mounds. Conclusions Overall, we conclude that termite mounds in this savanna form small refuges for tree species that seem less adapted to fire (more evergreens), have low nutrient availability (less nitrogen fixers) and suffer from water stress (larger leaf sizes) than typical savanna trees. Surprisingly, despite their reputation as browsing hotspots, the tree species dominating mounds are less nutritious and less preferred by browsers than tree species of the surrounding savanna, which may be explained by the relatively nutrient-rich nature of this savanna or intraspecific trait differences. [ABSTRACT FROM AUTHOR]- Published
- 2013
- Full Text
- View/download PDF
10. Ontogenetic niche shifts as a driver of seasonal migration.
- Author
-
Fokkema W, van der Jeugd HP, Lameris TK, Dokter AM, Ebbinge BS, de Roos AM, Nolet BA, Piersma T, and Olff H
- Subjects
- Animals, Population Dynamics, Reproduction, Seasons, Animal Migration, Salmon
- Abstract
Ontogenetic niche shifts have helped to understand population dynamics. Here we show that ontogenetic niche shifts also offer an explanation, complementary to traditional concepts, as to why certain species show seasonal migration. We describe how demographic processes (survival, reproduction and migration) and associated ecological requirements of species may change with ontogenetic stage (juvenile, adult) and across the migratory range (breeding, non-breeding). We apply this concept to widely different species (dark-bellied brent geese (Branta b. bernicla), humpback whales (Megaptera novaeangliae) and migratory Pacific salmon (Oncorhynchus gorbuscha) to check the generality of this hypothesis. Consistent with the idea that ontogenetic niche shifts are an important driver of seasonal migration, we find that growth and survival of juvenile life stages profit most from ecological conditions that are specific to breeding areas. We suggest that matrix population modelling techniques are promising to detect the importance of the ontogenetic niche shifts in maintaining migratory strategies. As a proof of concept, we applied a first analysis to resident, partial migratory and fully migratory populations of barnacle geese (Branta leucopsis). We argue that recognition of the costs and benefits of migration, and how these vary with life stages, is important to understand and conserve migration under global environmental change.
- Published
- 2020
- Full Text
- View/download PDF
11. Analyzing time-ordered event data with missed observations.
- Author
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Dokter AM, van Loon EE, Fokkema W, Lameris TK, Nolet BA, and van der Jeugd HP
- Abstract
A common problem with observational datasets is that not all events of interest may be detected. For example, observing animals in the wild can difficult when animals move, hide, or cannot be closely approached. We consider time series of events recorded in conditions where events are occasionally missed by observers or observational devices. These time series are not restricted to behavioral protocols, but can be any cyclic or recurring process where discrete outcomes are observed. Undetected events cause biased inferences on the process of interest, and statistical analyses are needed that can identify and correct the compromised detection processes. Missed observations in time series lead to observed time intervals between events at multiples of the true inter-event time, which conveys information on their detection probability. We derive the theoretical probability density function for observed intervals between events that includes a probability of missed detection. Methodology and software tools are provided for analysis of event data with potential observation bias and its removal. The methodology was applied to simulation data and a case study of defecation rate estimation in geese, which is commonly used to estimate their digestive throughput and energetic uptake, or to calculate goose usage of a feeding site from dropping density. Simulations indicate that at a moderate chance to miss arrival events ( p = 0.3), uncorrected arrival intervals were biased upward by up to a factor 3, while parameter values corrected for missed observations were within 1% of their true simulated value. A field case study shows that not accounting for missed observations leads to substantial underestimates of the true defecation rate in geese, and spurious rate differences between sites, which are introduced by differences in observational conditions. These results show that the derived methodology can be used to effectively remove observational biases in time-ordered event data.
- Published
- 2017
- Full Text
- View/download PDF
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