Retrodicting patch use by foraging swans in a heterogeneous environment using a set of functional responses

Effective conservation of important bird areas requires insight in the number of birds an area can support, and how this carrying capacity changes with habitat modifications. When food depletion is the dominant mechanism of competition, it should in principle be possible to calculate the total time foragers can spend per patch from their functional response (intake rate as a function of food density). However, in the field there are likely to be factors modulating the functional response. In this study previously published results of experiments on captive Bewick's swans were used to obtain functional responses of swans digging for tubers of Fennel pondweed on different foraging substrates: sandy and clayey sediment, and in shallow and deep water. In a field study, four 250×250 m sections belonging to different types (sandy–shallow, clayey–shallow, sandy–deep and clayey–deep) were delineated. Here tubers were sampled with sediment corers in three years, both before and after swan exploitation in autumn, and swans were observed and mapped from a hide in two of these years. Giving-up tuber biomass densities varied among sections. Substitution of these giving-up densities in the derived patch-type-specific functional responses yielded the quitting net energy intake rates in the four sections. As expected from the marginal value theorem, the quitting net energy intake rates did not vary among sections. Moreover, the observed foraging pressure (total foraging time per area) per patch type was in quantitative agreement with the integrated functional responses. These results suggest that in spatially heterogeneous environments, patch exploitation by foragers can be predicted from their functional responses after accounting for foraging substrate.

Burial depth distribution of fennel pondweed tubers (Potamogeton pectinatus) in relation to foraging by Bewick's swans

Deep burial in the sediment of tubers of fennel pondweed (Potamogeton pectinatus) has been explained in terms of avoidance by escape against consumption by Bewick's swans (Cygnus columbianus bewickii) in autumn. We therefore expected changes in foraging pressure to ultimately result in a change in the tuber distribution across sediment depth. A trade-off underlies this idea: deep tubers are less accessible to swans but must be larger to meet the higher energy demands of sprouting in spring. To test this prediction, we compared tuber burial depth over a gradient of foraging pressure both across space and across time. Tuber samples were obtained after aboveground plant senescence but before arrival of Bewick's swans. First, we compared the current tuber bank depth profile in a shallow lake with high foraging pressure, the Lauwersmeer, with that in two wetlands with moderate and low foraging pressure. Second, we compared the current tuber burial in the Lauwersmeer with that in the early 1980s when exploitation by swans had just started there. In accordance with our hypothesis, we found significantly deeper burial of tubers under high consumption risk compared to low consumption risk, both when comparing sites and comparing time periods. Since tubers in effect only survive to the next spring, the observed differences in burial depth among sites and over time cannot be a direct result of tuber losses due to consumption by swans. Rather, these observations suggest adaptive responses in tuber burial related to foraging pressure from Bewick's swans in the recent past. We thus propose that fennel pondweed exhibits flexible avoidance by escape, of a kind rarely described for plants, where both phenotypic plasticity and genotype sorting may contribute to the observed differences in tuber burial.

Swan foraging shapes spatial distribution of two submerged plants, favouring the preferred prey species

Compared to terrestrial environments, grazing intensity on belowground plant parts may be particularly strong in aquatic environments, which may have great effects on plant-community structure. We observed that the submerged macrophyte, Potamogeton pectinatus, which mainly reproduces with tubers, often grows at intermediate water depth and that P. perfoliatus, which mainly reproduces with rhizomes and turions, grows in either shallow or deep water. One mechanism behind this distributional pattern may be that swans prefer to feed on P. pectinatus tubers at intermediate water depths. We hypothesised that when swans feed on tubers in the sediment, P. perfoliatus rhizomes and turions may be damaged by the uprooting, whereas the small round tubers of P. pectinatus that escaped herbivory may be more tolerant to this bioturbation. In spring 2000, we transplanted P. perfoliatus rhizomes into a P. pectinatus stand and followed growth in plots protected and unprotected, respectively, from bird foraging. Although swan foraging reduced tuber biomass in unprotected plots, leading to lower P. pectinatus density in spring 2001, this species grew well both in protected and unprotected plots later that summer. In contrast, swan grazing had a dramatic negative effect on P. perfoliatus that persisted throughout the summer of 2001, with close to no plants in the unprotected plots and high densities in the protected plots. Our results demonstrate that herbivorous waterbirds may play a crucial role in the distribution and prevalence of specific plant species. Furthermore, since their grazing benefitted their preferred food source, the interaction between swans and P. pectinatus may be classified as ecologically mutualistic.

Hampered foraging and migratory performance in swans infected with low-pathogenic avian influenza A virus

It is increasingly acknowledged that migratory birds, notably waterfowl, play a critical role in the maintenance and spread of influenza A viruses. In order to elucidate the epidemiology of influenza A viruses in their natural hosts, a better understanding of the pathological effects in these hosts is required. Here we report on the feeding and migratory performance of wild migratory Bewick's swans (Cygnus columbianus bewickii Yarrell) naturally infected with low-pathogenic avian influenza (LPAI) A viruses of subtypes H6N2 and H6N8. Using information on geolocation data collected from Global Positioning Systems fitted to neck-collars, we show that infected swans experienced delayed migration, leaving their wintering site more than a month after uninfected animals. This was correlated with infected birds travelling shorter distances and fuelling and feeding at reduced rates. The data suggest that LPAI virus infections in wild migratory birds may have higher clinical and ecological impacts than previously recognised.

Animal–plant–microbe interactions : direct and indirect effects of swan foraging behaviour modulate methane cycling in temperate shallow wetlands

Wetlands are among the most important ecosystems on Earth both in terms of productivity and biodiversity, but also as a source of the greenhouse gas CH₄. Microbial processes catalyzing nutrient recycling and CH₄ production are controlled by sediment physico-chemistry, which is in turn affected by plant activity and the foraging behaviour of herbivores. We performed field and laboratory experiments to evaluate the direct effect of herbivores on soil microbial activity and their indirect effects as the consequence of reduced macrophyte density, using migratory Bewick’s swans (Cygnus columbianus bewickii Yarrell) feeding on fennel pondweed (Potamogeton pectinatus L.) tubers as a model system. A controlled foraging experiment using field enclosures indicated that swan bioturbation decreases CH₄ production, through a decrease in the activity of methanogenic Archaea and an increased rate of CH₄ oxidation in the bioturbated sediment. We also found a positive correlation between tuber density (a surrogate of plant density during the previous growth season) and CH₄ production activity. A laboratory experiment showed that sediment sterilization enhances pondweed growth, probably due to elimination of the negative effects of microbial activity on plant growth. In summary, the bioturbation caused by swan grazing modulates CH₄ cycling by means of both direct and indirect (i.e. plant-mediated) effects with potential consequences for CH₄ emission from wetland systems.

Explanations for variation in cognitive ability : behavioural ecology meets comparative cognition

Sara Shettleworth has played a defining role in the development of animal cognition and its integration into other parts of biology, especially behavioural ecology. Here we chart some of that progress in understanding the causes and importance of variation in cognitive ability and highlight how Tinbergen's levels of explanation provide a useful framework for this field. We also review how experimental design is crucial in investigating cognition and stress the need for naturalistic experiments and field studies. We focus particularly on the example of the relationship among food hoarding, spatial cognition and hippocampal structure, and review the conflicting evidence for sex differences in spatial cognition. We finish with speculation that a combination of Tinbergen and Shettleworth-style approaches would be the way to grapple with the as-yet unanswered questions of why birds mimic heterospecifics.

Distribution, ecology and conservation of small mammals in fire-prone landscapes

Management of fire for biodiversity conservation is a global issue. This research provides new insights into the distribution of mammals in fire-prone eco-systems. A key outcome of this thesis is that understanding the role of fire over broad spatial scales and long time periods will benefit ecological and conservation management.

Permanent genetic resources added to molecular ecology resources database 1 August 2010 – 30 September 2010

This article documents the addition of 229 microsatellite marker loci to the Molecular Ecology Resources Database. Loci were developed for the following species: Acacia auriculiformis · Acacia mangium hybrid, Alabama argillacea, Anoplopoma fimbria, Aplochiton zebra, Brevicoryne brassicae, Bruguiera gymnorhiza, Bucorvus leadbeateri, Delphacodes detecta, Tumidagena minuta, Dictyostelium giganteum, Echinogammarus berilloni, Epimedium sagittatum, Fraxinus excelsior, Labeo chrysophekadion, Oncorhynchus clarki lewisi, Paratrechina longicornis, Phaeocystis antarctica, Pinus roxburghii and Potamilus capax. These loci were cross-tested on the following species: Acacia peregrinalis, Acacia crassicarpa, Bruguiera cylindrica, Delphacodes detecta, Tumidagena minuta, Dictyostelium macrocephalum, Dictyostelium discoideum, Dictyostelium purpureum, Dictyostelium mucoroides, Dictyostelium rosarium, Polysphondylium pallidum, Epimedium brevicornum, Epimedium koreanum, Epimedium pubescens, Epimedium wushanese and Fraxinus angustifolia.

Fire, energy, and the ecology of reptiles in semi-arid Australia

‬Fire dependent ecosystems cover over half of the world's land surface. Understanding the factors that determine the distribution of fauna in these systems is essential to biodiversity conservation. This thesis explores the ecology of reptiles in a fire-prone region.

Changing philosophies and tools for statistical inferences in behavioral ecology

Recent developments in ecological statistics have reached behavioral ecology, and an increasing number of studies now apply analytical tools that incorporate alternatives to the conventional null hypothesis testing based on significance levels. However, these approaches continue to receive mixed support in our field. Because our statistical choices can influence research design and the interpretation of data, there is a compelling case for reaching consensus on statistical philosophy and practice. Here, we provide a brief overview of the recently proposed approaches and open an online forum for future discussion (https://bestat.ecoinformatics.org/). From the perspective of practicing behavioral ecologists relying on either correlative or experimental data, we review the most relevant features of information theoretic approaches, Bayesian inference, and effect size statistics. We also discuss concerns about data quality, missing data, and repeatability. We emphasize the necessity of moving away from a heavy reliance on statistical significance while focusing attention on biological relevance and effect sizes, with the recognition that uncertainty is an inherent feature of biological data. Furthermore, we point to the importance of integrating previous knowledge in the current analysis, for which novel approaches offer a variety of tools. We note, however, that the drawbacks and benefits of these approaches have yet to be carefully examined in association with behavioral data. Therefore, we encourage a philosophical change in the interpretation of statistical outcomes, whereas we still retain a pluralistic perspective for making objective statistical choices given the uncertainties around different approaches in behavioral ecology. We provide recommendations on how these concepts could be made apparent in the presentation of statistical outputs in scientific papers.

Feeding ecology of benthic invertebrates in an intermittently open estuary

Abundances of benthic invertebrates in the Hopkins River estuary were not affected by connection to the ocean, but by freshwater discharge and sediment properties. The bivalve Soletellina alba was identified as a suspension feeder. Invertebrate food sources were derived mainly from estuarine organic matter, but also contained marine and freshwater/terrestrial plants despite reduced river flow during drought conditions.