Foraging costs and accessibility as determinants of giving‐up densities in a swan‐pondweed system

Nolet, Bart A.; Fuld, Verinne N.; Rijswijk, Marielle E.C. Van

doi:10.1111/j.0030-1299.2006.13463.x

Cited by 57 publications

(54 citation statements)

References 43 publications

(71 reference statements)

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“…The birds usually arrive in the Lauwersmeer area in October and forage on the tubers of sago pondweed (Beekman et al 1991, Nolet et al 2001. The total time spent on tuber foraging in the Lauwersmeer is typically short, as after two to four weeks of massive swan presence numbers quickly drop as a fixed giving-up density of pondweed tubers is then attained (Nolet et al , 2006a. In the autumns (2003)(2004)(2005)(2006) preceding aboveground sampling in summer, 4000, 5500, 2800, and 1200 swan-days (swan days are the sum of daily swan counts) were recorded in the Babbelaar, respectively (Nolet et al 2006b; A. Gyimesi and B.…”

Section: Study System and Sitementioning

confidence: 99%

Compensatory growth in an aquatic plant mediates exploitative competition between seasonally tied herbivores

Hidding¹,

Nolet

Boer

et al. 2009

Ecology

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Abstract. The degree to which vertebrate herbivores exploitatively compete for the same food plant may depend on the level of compensatory plant growth. Such compensation is higher when there is reduced density-dependent competition in plants after herbivore damage. Whether there is relief from competition may largely be determined by the life-history stage of plants under herbivory. Such stage-specific compensation may apply to seasonal herbivory on the clonal aquatic plant sago pondweed (Potamogeton pectinatus L.). It winters in sediments of shallow lakes as tubers that are foraged upon by Bewick's Swans (Cygnus columbianus bewickii Yarrell), whereas aboveground biomass in summer is mostly consumed by ducks, coots, and Mute Swans. Here, tuber predation may be compensated due to diminished negative density dependence in the next growth season. However, we expected lower compensation to summer herbivory by waterfowl and fish as density of aboveground biomass in summer is closely related to photosynthetic carbon fixation. In a factorial exclosure study we simultaneously investigated (1) the effect of summer herbivory on aboveground biomass and autumn tuber biomass and (2) the effect of tuber predation in autumn on aboveground biomass and tuber biomass a year later. Summer herbivory strongly influenced belowground tuber biomass in autumn, limiting food availability to Bewick's Swans. In contrast, tuber predation in autumn by Bewick's Swans had a limited and variable effect on P. pectinatus biomass in the following growth season. Whereas relief from negative density dependence largely eliminates effects of belowground herbivory by swans, aboveground herbivory in summer limits both above-and belowground plant biomass. Hence, there was an asymmetry in exploitative competition, with herbivores in summer reducing food availability for belowground herbivores in autumn, but not the other way around.

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Section: Study System and Sitementioning

confidence: 99%

Compensatory growth in an aquatic plant mediates exploitative competition between seasonally tied herbivores

Hidding¹,

Nolet

Boer

et al. 2009

Ecology

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“…Predation risk also affects site use, in particular for small to medium-sized birds, and is often traded-off against food availability (Clark and Butler 1999;Guillemain et al 2007;Pomeroy et al 2006;Duijns et al 2009;Cresswell 1994). These are also the factors known to affect giving-up densities (GUDs), i.e., the food densities remaining after animals have left a food patch (Brown 1988;Nolet et al 2006a). Hence, GUDs at a stopover site have been proposed to reflect the long-term fuelling rates along the migration route (Van Gils and Tijsen 2007).…”

Section: Introductionmentioning

confidence: 99%

“…In Lauwersmeer, an important autumn staging site of Bewick's Swans in the Netherlands, within-year (i.e., spatial) variation in GUD was related to water depth (Nolet et al 2001b), largely due to differences in food accessibility and to a much lesser extent by differences in foraging costs (Nolet et al 2006a). Because accessibility is directly influenced by water levels, we hypothesize that inter-annual (i.e., temporal) variation in GUD at the stopover site is related to yearly differences in initial food density and water level.…”

Section: Introductionmentioning

confidence: 99%

Underuse of stopover site by migratory swans

Nolet

Gyimesi

2013

J Ornithol

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Many migratory birds use a chain of stopover sites to fuel their migration. Under time-minimizing migration, fuelling time and giving-up density at stopovers are predicted to depend on fuelling conditions. Fluctuations in food accessibility likely lead to changes in fuelling conditions, which should in turn be reflected in fuelling time and giving-up density. During their migration, Bewick's Swans Cygnus columbianus bewickii refuel on belowground tubers of Fennel Pondweed Potamogeton pectinatus in shallow lakes. We studied giving-up density and stopover use (expressed in bird-days) of Bewick's Swans at an autumn stopover site (Lauwersmeer, The Netherlands) during 1995-2008, as dependent on local environmental conditions. High water levels were hypothesized to restrict access to tuber stocks. High water levels at the stopover site were predicted to lead to higher giving-up densities and less bird-days spent at the stopover. Annual variation in givingup densities and number of bird-days was strongly associated with year-to-year differences in initial tuber biomass density and number of days with high water levels. As predicted, giving-up density increased and bird-days decreased with the number of days with high water level. We conclude that, in line with time-minimizing migration, changes in fuelling conditions may lead to underuse of a stopover site. Underuse of stopovers by migratory birds has been reported before but only in the sense that more food was left at stopover sites than at wintering sites. In contrast, in our case, dealing with a given stopover site, more food is left behind in some years than in other years.

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“…Jonzen et al (2002), Nolet et al (2006) and Raymond et al (2006) reported that tuber density of sago pondweed (Potamogeton pectinatus) affects the foraging of tundra swan (Cygnus columbianus bewickii) in Lake Lauwersmeer in the north of the Netherlands, while Sponberg & Lodge (2005) found that waterfowl in Lake Mattamuskeet, North Carolina, USA, gave up foraging when tuber density of wildcelery (Vallisneria americana) was below a certain threshold.…”

Section: Introductionmentioning

confidence: 99%

Will the Three Gorges Dam affect the underwater light climate of Vallisneria spiralis L. and food habitat of Siberian crane in Poyang Lake?

Leeuw²,

Skidmore³

et al. 2008

Hydrobiologia

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Almost 95% of the entire population of the Siberian crane (Grus leucogeranus) winter in Poyang Lake, China, where they forage on the tubers of the submerged aquatic macrophyte Vallisneria spiralis. The Three Gorges Dam on the Yangtze River may possibly affect this food source of the Siberian crane by affecting the light intensity reaching the top of the V. spiralis canopy. In this study, the photosynthetically active radiation at the top of the V. spiralis canopy (PAR tc ) in Lake Dahuchi was modeled from 1998 to 2006, and the potential impacts of changes in water level and turbidity on the underwater light climate of V. spiralis were analyzed. PAR tc was calculated from incident irradiance while the losses due to reflection at the water surface, absorption, and scattering within the water column were taken into consideration. The results indicated significant differences in PAR tc between years. Six years of water level and Secchi disk depth records revealed a seasonal switching of the lake from a turbid state at low water levels in autumn, winter, and spring to a clear state at high water levels during the monsoon in summer. The highest PAR tc occurred at intermediate water levels, which were reached when the Yangtze River forces Lake Dahuchi out of its turbid state in early summer and the water becomes clear. The intended operation of the Three Gorges Dam, which will increase water levels in May and June, may advance the moment when Lake Dahuchi switches from turbid to clear. We suggest that this might increase production of V. spiralis and possibly improve the food habitat conditions for wintering Siberian crane in Poyang Lake.

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Foraging costs and accessibility as determinants of giving‐up densities in a swan‐pondweed system

Cited by 57 publications

References 43 publications

Compensatory growth in an aquatic plant mediates exploitative competition between seasonally tied herbivores

Compensatory growth in an aquatic plant mediates exploitative competition between seasonally tied herbivores

Underuse of stopover site by migratory swans

Will the Three Gorges Dam affect the underwater light climate of Vallisneria spiralis L. and food habitat of Siberian crane in Poyang Lake?

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