The spatial complexity of seed movement: Animal‐generated seed dispersal patterns in fragmented landscapes revealed by animal movement models

Abstract

Large animals provide crucial seed dispersal services, yet face continued threats and are susceptible to changes in landscape composition and configuration. Thus, there is a growing imperative to improve understanding of animal‐generated seed dispersal using models that incorporate spatial complexity in a realistic, yet tractable, way. We developed a spatially explicit agent‐based seed dispersal model, with disperser movements informed by biotelemetry data, to evaluate how landscape composition and configuration affect seed dispersal patterns. We illustrated this approach for the world's second largest ratite, the emu (Dromaius novaehollandiae), a highly mobile generalist frugivore considered an important long‐distance disperser for many plant species across Australia. When animal movement is unrestricted, model parameters related to seed gut passage largely determine seed dispersal kernels. However, as habitat loss and fragmentation increase, the extent of long‐distance dispersal events is reduced and seed shadows became progressively more aggregated. This effect is due to the emu not being able to move between disconnected parts of the landscape, with small changes in habitat structure causing decreased long‐distance dispersal. We simulated seed dispersal patterns generated by three commonly used generic models of animal movement – unbiased and biased correlated random walks and Lévy walks – to evaluate how different representations of movement affect estimations of animal movements and emergent seed dispersal patterns. Simulated movements informed by the emu biotelemetry data resulted in longer median seed dispersal distances than do the three generic models. Synthesis. Changes in landscape composition and configuration can dramatically alter patterns of zoochorous seed dispersal as they influence animal movement. However, when models are used to simulate the patterns of seed dispersal, decisions about how animal movement is represented also affect estimates of seed dispersal.

The integrated role of resource memory and scent-based territoriality in the emergence of home-ranges

“…Another potential area of application is in animal-mediated seed dispersal research, which has identified the need to integrate frugivory and disperser movement (Côrtes & Uriarte 2013). A recent study highlighted the implications of using generic phenomenological movement representations (e.g., correlated random-walk) on dispersal model outcomes, and suggested more processbased movement approaches (Nield et al 2019).…”

Modeling mycorrhizal fungi dispersal by the mycophagous swamp wallaby (Wallabia bicolor)

“…In contrast, differences in dispersal distance and disperser effectiveness between species have been studied among frugivorous bird and seed‐harvesting ant assemblages. Any further examination of mammal‐mediated fungal spore dispersal should consider the relatively large body of literature produced on seed dispersal (e.g., Cousens, Hill, French, & Bishop, 2010; Jones & Muller‐Landau, 2008; Lehouck et al., 2009; Levin et al., 2003; Levey et al., 2008; Muller‐Landau et al., 2008; Nield et al., 2020; Spiegel & Nathan, 2007; Will & Tackenberg, 2008).…”

Diet composition of reintroduced Red-and-Green Macaws (Ara chloropterus) reflects gradual adaption to life in the wild

“…Although germination experiments would need the be conducted in order to confirm that the transported seeds are actually viable, we can expect that at least a portion of them will contribute to plant recruitment (Tella et al 2020). In a fragmented landscape like the wetlands, where ground connectivity between forest patches is restricted by flooded terrain, seed dispersal by terrestrial vertebrates is likely limited (Nield et al 2020). In this scenario, the presence of large bodied frugivorous birds such as the macaws can become vital to maintain gene flow between forest fragments, in particular of plant species with large seeds which cannot be transported by smaller birds (Baños-Villalba et al 2017).…”