Spatial Pattern of Adult Trees and the Mammal‐Generated Seed Rain In

Ecography 33: 545Á555, 2010 doi: 10.1111/j.1600-0587.2009.06052.x # 2010 The Authors. Journal compilation # 2010 Ecography Subject Editor: Kevin Burns. Accepted 21 July 2009 Spatial pattern of adult trees and the mammal-generated seed rain in the Iberian pear Jose M. Fedriani, Thorsten Wiegand and Miguel Delibes J. M. Fedriani and M. Delibes, Estacioń Biolo´gica de Donãna (CSIC), Avda. Ame´rico Vespucio s/n, Isla de la Cartuja, ES-41092 Sevilla. Á T. Wiegand, UFZ Helmholtz Centre for Environmental Research Á UFZ, Dept of Ecological Modeling, PF 500136, DE-04301 Leipzig, Germany. The degree to which plant individuals are aggregated or dispersed co-determines how a species uses resources, how it is used as a resource, and how it reproduces. Quantifying such spatial patterns, however, presents several methodological issues that can be overcome by using spatial point pattern analyses (SPPA). We used SPPA to assess the distribution of P. bourgaeana adult trees and their seeds (within fecal samples) dispersed by three mammals (badger, fox, and wild boar) within a 72-ha plot across a range of spatial scales. Pyrus bourgaeana trees in our study plot (n75) were clearly aggregated with a critical spatial scale of ca 25 m, and approximately nine randomly distributed tree clusters were identified. As expected from their marking behaviors, the spatial patterns of fecal deposition varied widely among mammal species. Whereas badger feces and dispersed seeds were clearly clustered at small spatial scales (B10 m), boar and fox feces were relatively scattered across the plot. A toroidal shift null model testing for independence indicated that boars tended to deliver seeds to the vicinity of adult trees and thus could contribute to the maintenance and enlargement of existing tree clusters. Badgers delivered feces and seeds in a highly clumped pattern but unlike boars, away from P. bourgaeana neighborhoods; thus, they are more likely to create new tree clusters than boars. The strong tree aggregation is likely to be the result of one or several non-exclusive processes, such as the spatial patterning of seed delivery by dispersers and seedling establishment beneath mother trees. In turn, the distinctive distribution of P. bourgaeana in Donãna appeared to interact with the foraging behavior of its mammalian seed dispersers, leading to neighbourhood-specific dispersal patterns and fruit-removal rates. Our study exemplifies how a detailed description of patterns generates testable hypotheses concerning the ecology of zoochorous. Pyrus bourgaeana dispersers were unique and complementary in their spatial patterning of seed delivery, which likely confers resilience to their overall service and suggests lack of redundancy and expendability of any one species. Patchiness, or the degree to which plant individuals are recovering this ‘‘hidden’’ information (Wiegand et al. aggregated or dispersed, co-determines how a species uses 2003, 2007, 2009, Wiegand and Moloney 2004, Grimm resources, how it is used as a resource, and how it reproduces et al. 2005, McIntire and Fajardo 2009). However, too (Condit et al. 2000, Wiegand et al. 2007). For instance, the simple or imprecise analytical tools have often hindered spatial distribution of plants can influence the movements of linking the observed patterns to processes (McIntire and frugivores leading to neighbourhood-specific dispersal pat- Fajardo 2009 and references therein). terns and fruit-removal rates where isolated plants are less One of the most important methodological issues in this often visited than plants growing in clusters (Carlo and respect is the use of oversimplified null models which does Morales 2008). In turn, seed dispersers often influence the not allow the characterization of the different features of spatial distribution of plants by establishing the initial spatial patterns in enough detail for meaningful inference template on which post-dispersal processes act (e.g. seed (Schurr et al. 2004, Wiegand and Moloney 2004, Wiegand survival, germination, seedling survival, establishment; et al. 2007, McIntire and Fajardo 2009). However, spatial Fragoso 1997, Russo and Augspurger 2004). Therefore, patterns have many features that can be revealed when plant-frugivore interactions can be seen as a dynamic two- appropriate techniques are used. For example, earlier way process in which the interacting organisms (plants and applications of spatial pattern analysis in ecology have seed dispersers) mutually affect their spatial patterns at a compared the observed patterns only with random patterns. range of scales. The emerging spatial patterns, e.g. the This approach can reveal the range of scales with significant pattern of adult plants and the pattern of seed dispersal, are aggregation, but does not provide further information such therefore expected to conserve signals from the underlying as the number of clusters, the average size of clusters, or if processes, and precise spatial pattern analysis can help the pattern is likely to be a superposition of independent 545 patterns with different characteristics (Wiegand et al. 2007, consecutive fruiting seasons to address four objectives: 2009). However, clustered patterns may be the rule rather 1) to characterize the spatial distribution of adult trees, than the exception (Condit et al. 2000, Wiegand et al. 2) to characterize the spatial distribution of seeds delivered 2007) and, especially in the case of plant populations by each disperser, 3) to assess the spatial relationship dispersed by several frugivores with contrasting behaviors between the distribution of adult trees and the seed rain (e.g. scatter- and clump-dispersal; Howe 1989), seed rain generated by each disperser, and 4) to find out if P. is expected to show a superposition of patterns. bourgaeana seeds were more frequent in mammal deposi- Spatial point pattern analysis (SPPA; Diggle 2003, Illian tion sites closer to adult P. bourgaeana trees. We then et al. 2008) deals with the statistical analysis of mapped discuss in light of our pattern analysis several hypotheses on point patterns, which comprise the coordinates and addi- the processes acting in this plant-frugivore system and the tional features of ecological objects. The assumption is that consequences of our results for dispersal service resilience the objects can be approximated as points (but see Wiegand and implications for conservation. et al. 2006) and that either all points are mapped within a given study site or a random sample of all points. Second- order statistics such as the pair correlation function or Methods Ripley’s K are the summary statistics of choice for describing the characteristics of point patterns (e.g. cluster- Study system and site ing) over a range of spatial scales (Stoyan and Stoyan 1994, Wiegand and Moloney 2004, Law et al. 2009). Addition- Pyrus bourgaeana (Rosaceae) is a monoecious small tree ally, they can be applied in conjunction with realistic null (typically 3Á6 m in height) distributed across the southern models to help in the identification of the underlying Iberian Peninsula and northern Morocco (Aldasoro et al. patterns (Schurr et al. 2004, Wiegand and Moloney 2004, 1996). Our focal population is located in the Donãna Wiegand et al. 2007, McIntire and Fajardo 2009). National Park (510 km2;3789?N, 6826?W; elevation In this study, we applied recent extensions of SPPA to 0Á80 m), on the west bank of the Guadalquivir River better understand the processes that determined the spatial estuary in southwestern Spain. In the Donãna area, pattern of adult trees in the Iberian pear, Pyrus bourgaeana, P. bourgaeana distribution is very fragmented, with trees in southwester Spain. In our study region, P. bourgaeana occurring at low densities (generallyB1 individual ha1) appears to be distributed in clusters (Fedriani and Delibes in several Mediterranean scrubland patches that are isolated 2009a) though no formal analyses of the spatial patterns from each other by marshes, sand dunes, or cultivations. have been undertaken for this species. The spatial structure The climate is Mediterranean sub-humid, characterized by of P. bourgaeana is likely to be the result of several non- dry, hot summers (JuneÁSeptember) and mild, wet winters exclusive processes, including edaphic variables (Clark et al. (NovemberÁFebruary). Annual rainfall varies widely, ran- 1999), establishment beneath mother trees (Chapman and ging during the last twenty-five years from 170 to 1028 mm Chapman 1995), and the pattern of seed delivery by its seed (mean9SD583.09221.1 mm). Though most rain dispersers (Russo and Augspurger 2004). Therefore, we also (Â80%) falls between OctoberÁMarch, there is a marked assessed the spatial patterns of P. bourgaeana seed rain interannual seasonal variability in rainfall. For example, the generated by its dispersers, as well as its potential relation- coefficients of variation for summer and winter rainfall were ship with the local patterning of adult tree distribution. The 93.3 and 54.4%, respectively, between 1984 and 2005. main local dispersers of P. bourgaeana are the Eurasian In our study population the understory is dominated by badger Meles meles, the wild boar Sus scrofa, and the red fox Pistacia lentiscus shrubs growing singly or in small clumps Vulpes vulpes (Fedriani and Delibes 2009a). Disperser- separated by unvegetated sandy substrate or sparse Hali- specific mobility (Spiegel and Nathan 2007), habitat mium halimifolium, Ulex spp., and Chamaerops humilis preferences (Jordano

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