Recovery of Potamogeton pectinatus L. stands in a shallow eutrophic lake under extreme grazing pressure

Hilt, Sabine

doi:10.1007/s10750-006-0167-3

Cited by 38 publications

(34 citation statements)

References 15 publications

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“…By means of the modelling study presented here, we can now generalize this finding for a range of bird densities and nutrient loadings. The range of chosen bird densities during summer that we used in our study (5-50 coots ha -1 ) encompasses densities as reported from field observations (Lauridsen et al, 1993;Sondergaard et al, 1996;Hilt, 2006). When bird herbivory was added at such densities to the food web, the critical nutrient loading (CNL) during eutrophication was lower than the CNL in the situation where birds were absent.…”

Section: Discussionmentioning

confidence: 99%

“…3), that is at the point where the resilience of the clearwater state breaks down (the clear-water state ceases to be a basin of attraction). Therefore, herbivory by birds has a synergistic effect with mechanisms that erode the resilience of the clear-water state during eutrophication, in particular shading by phytoplankton and periphyton in the case of freshwater lakes (Weisner et al, 1997;Hilt, 2006;Hidding et al, 2010). For very low nutrient loadings, however, bird impact decreased with increasing nutrient loading.…”

Section: Discussionmentioning

confidence: 99%

“…the relative change of macrophyte biomass compared to the situation without birds, has been used in many field studies with exclosure experiments (e.g. Perrow et al, 1997;Hilt, 2006;Hidding et al, 2010). The outcomes of these experiments were extremely variable, with bird impact ranging from zero or a few percent difference to 100% difference (i.e.…”

Section: Discussionmentioning

confidence: 99%

“…Grazing waterbirds, such as coots, swans, and ducks, can visit lakes in large numbers and feed on roots and shoots of submerged macrophytes. Some studies found that herbivory by birds decreased macrophyte biomass severely, even up to 100% (Sondergaard et al, 1996;Hilt, 2006;Wood et al, 2012;Bakker & Nolet, 2014), while others found that the removed biomass is compensated by macrophyte regrowth (Mitchell & Wass, 1996;Perrow et al, 1997;Hansson et al, 2010). This apparent contradiction may arise from the varying conditions under which these studies have been conducted, such as the macrophyte and the bird species under consideration, or the experimental set-up (Perrow et al, 1997;Bakker et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

“…It has been hypothesized that the impact of grazing birds on macrophytes varies with the nutrient status of the lake (Perrow et al, 1997;Weisner et al, 1997;Hansson et al, 2010;Bakker & Nolet, 2014). Possible mechanisms for this could be that under eutrophic conditions plants have a higher nutrient content relative to their carbon content, making them more preferred food (Bakker & Nolet, 2014), and that plants have less tolerance to grazing due to increased periphyton growth on the macrophytes (Weisner et al, 1997;Hilt, 2006;Hidding et al, 2010). These mechanisms could lead to a higher impact of herbivory by birds under more eutrophic but still transparent conditions.…”

Section: Introductionmentioning

confidence: 99%

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The impact of bird herbivory on macrophytes and the resilience of the clear-water state in shallow lakes: a model study

et al. 2016

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Shallow lakes have the potential to switch between two alternative stable states: a clear macrophyte-dominated and a turbid phytoplankton-dominated state. Observational and experimental studies show that in some lakes herbivory by birds may severely decrease macrophyte biomass, while in other lakes, the removed biomass by herbivory is compensated by regrowth. These contradictory outcomes might arise because of interplay between top-down control by bird herbivory and bottom-up effects by nutrient loading on macrophytes. Here, we use the ecosystem model PCLake to study top-down and bottom-up control of macrophytes by coots and nutrient loading. Our model predicted that (1) herbivory by birds lowers the critical nutrient loading at which the regime shift occurs; (2) bird impact on macrophyte biomass through herbivory increases with nutrient loading; and (3) improved food quality enhances the impact of birds on macrophytes, thus decreasing the resilience of the clear-water state even further. The fact that bird herbivory can have a large impact on macrophyte biomass and can facilitate a regime shift implies that the presence of waterfowl should be taken into account in the estimation of critical nutrient loadings to be used in water quality management.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The impact of bird herbivory on macrophytes and the resilience of the clear-water state in shallow lakes: a model study

et al. 2016

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Nonlinear effects of food aggregation on interference competition in mallards

Gyimesi

Rooij

Nolet

2010

Behav Ecol Sociobiol

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Previous studies of interference competition have shown an asymmetric effect on intake rate of foragers on clumped resources, with only subordinate individuals suffering. However, the food distributions in these studies were uniform or highly clumped, whereas in many field situations, food aggregation is intermediate. Here we investigated whether food distribution (i.e., uniform, slightly clumped, and highly clumped) affects the behavioral response of mallards foraging alone or competing with another. Although the amount of food was the same in all distributions, the mallards reached higher intake rates, visited fewer patches, and showed longer average feeding times in the highly clumped distribution. Competing mallards had lower intake rates on the slightly clumped than on the uniform or highly clumped food distributions. Subordinates generally visited more patches and had shorter feeding times per patch, but their intake rates were not significantly lower than those of dominants. Therefore, we propose that subordinates do not necessarily suffer from interference competition in terms of intake rate, but do suffer higher search costs. In addition, although dominants had significantly higher average feeding times on the best quality patches of the highly clumped food distribution, such an effect was not found in the slightly clumped distribution. These findings indicate that in environments where food is aggregated to a lesser extent, monopolization is not the best strategy for dominants. Our results suggest that interference experiments should use food distributions that resemble the natural situation animals are faced with in the field.

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Above- and below-ground vertebrate herbivory may each favour a different subordinate species in an aquatic plant community

et al. 2009

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At least two distinct trade-oVs are thought to facilitate higher diversity in productive plant communities under herbivory. Higher investment in defence and enhanced colonization potential may both correlate with decreased competitive ability in plants. Herbivory may thus promote coexistence of plant species exhibiting divergent life history strategies. How diVerent seasonally tied herbivore assemblages simultaneously aVect plant community composition and diversity is, however, largely unknown. Two contrasting types of herbivory can be distinguished in the aquatic vegetation of the shallow lake Lauwersmeer. In summer, predominantly above-ground tissues are eaten, whereas in winter, waterfowl forage on below-ground plant propagules. In a 4-year exclosure study we experimentally separated above-ground herbivory by waterfowl and large Wsh in summer from below-ground herbivory by Bewick's swans in winter. We measured the individual and combined eVects of both herbivory periods on the composition of the three-species aquatic plant community. Herbivory eVect sizes varied considerably from year to year. In 2 years herbivore exclusion in summer reinforced dominance of Potamogeton pectinatus with a concomitant decrease in Potamogeton pusillus, whereas no strong, unequivocal eVect was observed in the other 2 years. Winter exclusion, on the other hand, had a negative eVect on Zannichellia palustris, but the eVect size diVered considerably between years. We suggest that the colonization ability of Z. palustris may have enabled this species to be more abundant after reduction of P. pectinatus tuber densities by swans. Evenness decreased due to herbivore exclusion in summer. We conclude that seasonally tied above-and below-ground herbivory may each stimulate diVerent components of a macrophyte community as they each favoured a diVerent subordinate plant species.

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Recovery of Potamogeton pectinatus L. stands in a shallow eutrophic lake under extreme grazing pressure

Cited by 38 publications

References 15 publications

The impact of bird herbivory on macrophytes and the resilience of the clear-water state in shallow lakes: a model study

The impact of bird herbivory on macrophytes and the resilience of the clear-water state in shallow lakes: a model study

Nonlinear effects of food aggregation on interference competition in mallards

Above- and below-ground vertebrate herbivory may each favour a different subordinate species in an aquatic plant community

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