Wild geese of the Yangtze River: their ecology and conservation Yong Zhang Thesis committee Promotor Prof. Dr H.H.T. Prins Professor of Resource Ecology Wageningen University Co-promotors Dr W.F. de Boer Associate Professor, Resource Ecology Group Wageningen University Prof. Dr Lei Cao Professor of Ecology Chinese Academy of Sciences Other members Prof. Dr P.J.H. Reijnders, Wageningen University Dr B.S. Ebbinge, Wageningen University Dr M.J.J.E. Loonen, University of Groningen Dr B.A. Nolet, Netherlands Institute of Ecology, Wageningen This research was conducted under the auspices of the C. T. de Wit Graduate School of Production Ecology & Resource Conservation Wild geese of the Yangtze River: their ecology and conservation Yong Zhang Thesis submitted in fulfilment of the requirements for the degree of doctor at Wageningen University by the authority of the Rector Magnificus Prof. Dr. A.P.J. Mol, in the presence of the Thesis Committee appointed by the Academic Board to be defended in public on Thursday 7 January 2016 at 11.00 a.m. in the Aula. Yong Zhang Wild geese of the Yangtze River: their ecology and conservation 146 pages. PhD Thesis, Wageningen University, Wageningen, NL (2016) With references, with summaries in Dutch and English ISBN: 978-94-6257-604-9 Table of Contents Chapter 1 General introduction…………………………………….……………………1 Chapter 2 Experimental evidence shows the importance of behavioural plasticity and body size under competition in waterfowl……………………………………………….9 Chapter 3 Elevation and sward height gradient facilitate coexistence of goose species through allometric responses in wetlands………………………….…………………...33 Chapter 4 Individual-area relationship best explains goose species density in wetlands………………………………………………………………………………...45 Chapter 5 Effect of protection status and ecological variables on Anatidae species population sizes in wetlands of the Yangtze River…………………………………….61 Chapter 6 Synthesis…………………………………………………………………….97 References…………………...…………………………………..….............................112 Summary……………………...……………………………………………………….133 Samenvating……………………………………………………………………….…..136 Affiliation of Co-authors…………………………………………...………………....139 Acknowledgements……………………………………………......………………….140 Curriculum vitae……………………………………………….…………………...…142 List of Publications……………………………………………………………………143 PE&RC PhD Education Certificate…...……………………………............................145 Chapter 1 General introduction Yong Zhang 1 Chapter 1 General introduction One of the fundamental issues in ecology and conservation biology is to explain and predict the distribution of organisms. Where animals can be found is determined by their movement decisions; these decisions are in turn based on the interplay between their needs and what the environment is offering them as determined by meteorological factors, water availability, availability of food resources, human disturbance or predation risk. Despite exhaustive research efforts during the past decades, this issue remains incompletely understood, partly because distribution and abundance of animals can be determined by a variety of abiotic and biotic factors that interact and operate at different spatial scales. Moreover, biotic interactions, such as top-down and bottom-up processes, operate across trophic levels (Krebs et al. 1995), and within the same trophic level, competitive and facilitative interactions take place at the same time (Schoener 1983, Reiter and Andersen 2013, Tombre et al. 2013). The foragers’ spatial distribution is, among other factors, a consequence of adaptive foraging behaviour when foraging in a heterogeneous environment. The selection of these areas is described in, for instance, the optimal foraging theory. The optimal foraging theory (Emlen 1966, MacArthur and Pianka 1966) assumes that a predator selects preys which maximize its profitability. Thus, animals will either try to maximize energy intake or minimize time spent to obtain a fixed amount of energy (Bergman et al. 2001, Fryxell et al. 2004). For example, ungulates modified their behaviour according to a time-minimizing strategy (Kie 1999). Great tits (Parus major) exploited patchily distributed prey following the optimal forage theory (Cowie 1977). Starlings (Sturnus vulgaris) used different foraging modes to maximize the net rate of energy gain per unit of time (Bautista et al. 2001). The ideal free distribution is frequently employed when studying animal habitat selection and distribution. This theory states that individual animals will aggregate in various patches proportionate to the amount of resources available in each patch (Fretwell and Calver 1969). For instance, ovenbird (Seiurus aurocapilla) density was adjusted to match the habitat condition with changing habitat size, supporting the ideal 2 General Introduction free distribution (Hache et al. 2013). However, the ideal despotic distribution, whereby more experienced or competitive individuals occupy the habitat where they can maximize their fitness and thereby force the other individuals into the lower quality area (Petit and Petit 1996, Calsbeek and Sinervo 2002), tends to receive more support than the ideal free distribution (Rodenhouse et al. 1997, Piper 2011). Hence, when the resources are limited, interference competition becomes an important factor affecting animal habitat selection. Interference competition usually incorporates a social component, some individuals being denied access to resources by the (often aggressive) actions of others (Van Dijk et al. 2012). Through social interactions and aggressive encounters between competitors, the “superior species” may control the best patches whereas subordinates are forced to sub-optimal habitat where they experience a reduction in intake rate (Smith et al. 2001, Vahl 2006). For instance, the “subordinate species”, Greenland white-fronted geese (Anser albifrons flavirostris), shifted to sub- optimal feeding patches with lower food quality and increased their foraging time under competition with “superior” Canada geese (Branta canadensis) (Kristiansen and Jarrett 2002). The authors predicted that the Greenland white-fronted geese could compensate for the lower energy intake in this way. Hence, interference competition is an important mechanism that determines differences in feeding patch selection and intake rate in competing species. The ideal free distribution should also take spatial differences in resource quality and quantity into account. Hassall and Lane (2005) argued that goose species should not follow the predictions derived from the ideal free distribution because they are constrained by nitrogen content of the forage. Moreover, the availability of food resources often exhibit typical spatial and temporal variation in terms of quality and quantity (Fryxell et al. 2005) that can also affect the spatial distribution and abundance of geese. In general, foods with a higher protein content and a lower fibre content have a higher digestibility (Prop and Vulink 1992) and are hence more attractive to especially smaller bodied species, whereas larger species prefer a higher intake rate, are less sensitive to variation in forage quality, and therefore select taller swards (Durant et al. 2003, Durant et al. 2004, Heuermann et al. 2011). Several theories with regard to foraging behaviour (what to eat?) and decisions with regard to location choice (where to eat?) have been formulated based on the researches on different herbivores, such as cattle, sheep, goats and geese. The intake rate 3 Chapter 1 maximization theory predicts that herbivores select patches offering the highest dry matter intake rate (Kenney and Black 1984). However, forage quality generally decreases with increasing biomass (Prins et al. 1998). When the swards grow, their quality will become poorer as the fibre content increases (Prop and Vulink 1992) and the nutrient content decreases (Hassall et al. 2001). For this reason, the forage maturation hypothesis has been formulated (Riddington et al. 1997, Heuermann et al. 2011). According to this hypothesis, herbivores should select the patches with intermediate plant biomass because under these conditions the patches not only offer higher dry matter intake but also higher nutrient intake. This hypothesis was confirmed by studies on geese (Riddington et al. 1997, Heuermann et al. 2011). Durant et al. (2004) showed that Anatidae species with different body sizes selected different feeding patches. When foraging together in a heterogeneous environment, larger species foraged on taller swards, while smaller species selected lower swards, although both species could maximize their protein intake. However, another study showed that there was no significant relationship between forage quality and grazing intensity based on results obtained from geese foraging on semi-natural areas (Si et al. 2011). The authors of the latter paper discussed that this absence of an effect of forage quality is perhaps because the grasses in their study area had such a high nutrient content that the nutrient requirements of these geese were always satisfied. So, intake rate maximization might not offer the best strategy, as animal often face a trade-off between foraging quality and quantity, mediated by body size. The allometric scaling laws (Bell 1970, Jarman 1974) predict that animals differing in body size respond differently to environmental factors based on physiologic and digestive constraints of body size. Hence, predictions derived from foraging theories suggest that herbivores select their habitat