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Appendix S1.
Extended explanation of the material and methods for the GIS-generated variables and field sampling.
We quantified the following variables in each patch (study unit):
UTMX and UTMY. X and Y coordinates, as the UTM of the centroid of each patch.
Elevation (m) and Slope (º). The mean value for each patch obtained using a Digital Elevation Model (DEM) with 30m-pixel size (Junta de Andalucía, Consejería de Medio Ambiente).
Area (ha). As an estimate of patch size. Calculated from the patch polygon generated by photo interpretation.
Normalized Perimeter. The actual perimeter of patch divided by that of a circle with the same area, as an indicator of patch shape.
Landscape Irradiance. We created the limit angles responsible for the shading models, taking into account latitude, sun position, incidence angles, projected shades and the distance from the Earth to the sun. We then calculated the total solar radiation for a typical day per patch, and multiplied it by the number of days per month. Finally, we obtained the total radiation per patch (in KJ/ (m2·micrometer)(2 bytes/pixel)) by adding up the radiation of all the pixels on each patch. For further analysis we used total summer radiation, using the sum of the data from June, July and August. We selected this period because it corresponds to the summer drought, the main cause of one-year-old seedling mortality in Q. ilex (Gómez 2004; Puerta-Piñero et al. 2007). In Mediterranean areas, irradiance is usually highly correlated with temperature and soil water content (Ramirez et al. 2006; Gómez-Aparicio et al. 2005), so we used irradiance as a surrogate for these abiotic factors.
Patch Irradiance. Calculated by multiplying the total irradiance per patch (calculated from the abovementioned GIS) by the average irradiance per habitat type (oak woodland, pine woodland or shrubland, according to the mean values in this habitat type from hemispherical photographs, see below) to obtain mean summer irradiance per patch (Ipatch).
Microhabitat Irradiance. Irradiance at the microsite scale (Imicroh) was estimated for a subset of seedlings (different from the ones sampled in this study) in each microhabitat (reported in Puerta-Piñero et al. 2007) using the Global Site Factor (GSF), which corresponds to the proportion of full sunlight penetrating the forest canopy, which is inversely related to canopy plant cover (Ramírez et al. 2006). It combines direct radiation (DSF), by calculating the annual solar track, and diffuse radiation (ISF), based on a uniform overcast sky model (Ramírez et al. 2006; Puerta-Piñero et al. 2007). GSF was estimated from hemispherical photographs taken at a height of 0.25 m above the ground using a horizontally-levelled digital camera (CoolPix 995 digital camera, Nikon, Tokyo, Japan) focused to the zenith, using a fish-eye lens of 180o (FCE8, Nikon). All the photographs were taken after ensuring a homogeneous illumination of the overstorey canopy and correct contrast between the canopy and the sky. Photographs were analyzed using Hemiview canopy analysis software version 2.1 (1999, Delta-T Devices Ltd, Cambridge, UK). As GSF values were estimated for a different set of seedlings, microhabitat irradiance (Imicroh) was estimated by multiplying Ipatch by the mean GSF values computed from the microhabitats where seedlings were found in each patch.
Acorn production. We estimated acorn production in the falls of 2004 and 2005 in five randomly-selected adult oaks per patch on all the oak woodlands patches. We used a semi-quantitative scale with five categories, ranging from 0 (no acorns), 1 (1-25% of branches bearing acorns), 2 (25-50%), 3 (50-75%), and 4 (100% of the branches in the canopy full of acorns), thereby obtaining accurate and quick approximations of the total crop when quantitative methods are not affordable (Herrera et al. 1994). We estimated the acorn production per patch by multiplying the mean production per tree and the number of trees per patch. Neither shrublands nor pine woodlands had reproductive Holm oak trees on the study site.
Jay flights. Estimated in 2004 and 2005 by observing jays moving acorns across the study area during the natural dispersal period (October–December). Observations were carried out from sunrise to sunset from five strategic positions. Their location made it possible to track the jays’ flight paths after feeding on acorns and scan the whole study area, including all the patches in the Huenes watershed; the other watersheds were not sampled due to difficult accessibility and lack of time. After personal observations in the area, we believe that the behavior on the three watersheds appears to be similar. The observation time per patch was nearly equivalent for all the patches, and thus the differences in arrival flights per patch were due to differences in jay behavior and not different numbers of observations per patch (see Gómez 2003 for similar methods). The Gómez (2003) study was performed on the same study site, with the same study species (and probably even the same individual jays) studied in the same way, and it reported that virtually all the flights starting in oak woodlands are in fact acorn dispersal flights.
We obtained a total of 491 destination flights from all the 34 patches in the Huenes watershed (of the 62 total patches for the whole study). For further analysis, we considered the sum of destination flights per patch.
Mice burrows, feeders and eaten acorns
Rodent activity. We estimated relative densities of rodents once a year during the falls of 2004 and 2005 by randomly establishing three 100 m2 (2 m x 50 m) transects per patch. We recorded the number of 1) woodmouse burrows, 2) eaten acorns, and 3) feeders (considered as the presence of more than two eaten acorns in the same place, within <20cm radius). Woodmouse burrows were identified by small holes in the ground surface while acorns eaten by woodmice were easily identifiable by clear gnaw marks, as compared to marks from other rodents. Woodmouse feeders were considered as the presence of at least two eaten acorns in the same place.
We monitored 3.72 ha of the total area for each variable; all 62 patches of the study site were included, and the mean values of each variable were computed for each patch before analysis. In total, we found 12 woodmouse burrows, 1,132 eaten acorns and 40 feeders.
Wild-boar feces and rootings. Inferred by using three random 200 m2 (4mx50m) transects per patch, in which we counted the number of feces and rootings (total of 3.72 ha monitored on all the 62 patches) in fall 2004, with a total of 180 feces and 2,378 rootings. We computed the mean values of each variable per patch before the analysis.
Wild-boar feces were easily recognizable via visual inspection (Massei et al. 1997), with no similar feces of other animals in the area (authors’ personal observation). Wild-boar rooting was only considered when there was clear evidence of wild-boar activity and was counted only when we found apparently separate traces (Meriggi and Sachi 2000). This measurement is a cumulative estimate of wild-boar activity, since it represents the number of rootings present on the patch immediately before the data were collected.
% shoots eaten by big mammal herbivores. Using the abovementioned transects, in fall 2004 we measured mammalian herbivore damage per patch (mainly caused by the Spanish ibex Capra pyrenaica and livestock) as the proportion of apical shoots consumed by ungulates in a subgroup of 703 saplings (of the total 1,078 found on all the transects). This measurement was made by visual inspection, by counting the total number of shoots as well as the number of shoots with visible damage (Zamora et al. 2001). The proportion of damaged shoots represents a cumulative estimate of herbivory intensity, since it is the percentage of shoots removed by ungulates over time.
Connectivity. We modeled five spatial scenarios of patch connectivity summarizing the behavior reported in the study area by the main acorn dispersal agents (Gómez 2003; Gómez et al. 2008), as follows:
Connectivity based on barochory acorn dispersal (0m). Assuming abiotic acorn dispersal by gravity (barochory), with dispersal distance = 0 m (and thus an equivalent value of α = 1)
Connectivity based on dispersal by rodents (average-distance=1m). Assuming mean acorn dispersal distance by rodents, with dispersal distance = 1 m (α = 0.5).
Connectivity based on dispersal by rodents (long-distance=4m). Assuming maximum acorn dispersal distance by rodents (4 m, α = 0.25)
Connectivity based on dispersal by jays (average-distance=100 m). Assuming mean acorn dispersal distance by Eurasian jay, (100 m, α = 0.001)
Connectivity based on acorn dispersal by jays (long-distance=400 m). Assuming maximum acorn dispersal distance by jays (400 m, α = 0.00025)
All the GIS variables were calculated using MiraMon (http://www.creaf.uab.cat/miramon).
References (not included in the main manuscript)
Gómez-Aparicio L, Gómez JM, Zamora R, Boettinger JL (2005). Canopy vs. soil effects of shrubs facilitating tree seedlings in Mediterranean montane ecosystems. Journal of Vegetation Science, 16, 191–198.
Meriggi A, Sacchi O (2001) Habitat requirements of wild boars in the northern Apennines (N Italy): A multi-level approach. Italian Journal of Zoology 68 (1): 47–55.
Massei G, Genov PV, Staines BW, Gorman ML (1997) Factors influencing home range and activity of wild boar (Sus scrofa) in a Mediterranean coastal area. Journal of Zoology 242 (3): 411–423.
Figure S1: Landscape structure and geographical position of the study sites. Black areas correspond to oak woodland patches, dark gray to pine woodland patches, and light gray to shrublands. White areas are other landscape units, mainly open or urban areas.
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Table S1. Correlation matrix between all the variables studied
S / 1yS / 2yS / MB / MF / EA / WBF / WBR / h / Sl / A / P / H / J / AP / Ip / Im / X / Y / C0 / C1 / C4 / C100 / C400Saplings (S) / 1.0 / 0.6 / 0.7 / 0.0 / 0.1 / 0.1 / -0.5 / 0.1 / -0.3 / -0.5 / 0.0 / -0.1 / -0.5 / 0.3 / -0.4 / -0.3 / -0.4 / 0.1 / -0.4 / 0.0 / 0.0 / 0.0 / -0.2 / -0.1
1 yr Seedling (1yS) / 1.0 / 0.9 / -0.1 / 0.3 / 0.6 / -0.4 / 0.1 / -0.3 / -0.4 / 0.1 / 0.0 / -0.5 / 0.2 / -0.6 / -0.2 / -0.5 / -0.1 / -0.3 / 0.0 / 0.0 / 0.0 / -0.1 / 0.1
2 yr Seedling (2yS) / 1.0 / -0.1 / 0.1 / 0.4 / -0.5 / 0.2 / -0.2 / -0.4 / 0.2 / 0.0 / -0.4 / 0.3 / -0.5 / -0.3 / -0.5 / 0.1 / -0.4 / 0.2 / 0.2 / 0.2 / -0.1 / 0.1
Mice Burrows (MB) / 1.0 / 0.1 / -0.1 / 0.1 / -0.3 / -0.1 / -0.1 / -0.2 / -0.2 / -0.1 / -0.1 / -0.2 / 0.2 / 0.4 / 0.2 / -0.4 / -0.3 / -0.3 / -0.3 / -0.4 / -0.2
Mice Feeders (MF) / 1.0 / 0.7 / -0.3 / -0.3 / -0.3 / -0.3 / -0.3 / -0.3 / -0.3 / 0.2 / 0.0 / 0.3 / 0.0 / 0.1 / -0.5 / -0.4 / -0.4 / -0.4 / -0.5 / -0.4
Eaten Acorns / 1.0 / -0.3 / -0.3 / -0.3 / -0.2 / -0.2 / -0.3 / -0.2 / -0.2 / -0.2 / 0.2 / -0.2 / -0.1 / -0.3 / -0.3 / -0.3 / -0.4 / -0.4 / -0.4
WB Feces (WBF) / 1.0 / -0.1 / 0.2 / 0.0 / -0.1 / 0.0 / 0.2 / -0.1 / 0.1 / 0.2 / 0.4 / -0.1 / 0.4 / -0.1 / 0.0 / 0.0 / 0.3 / 0.2
WB Rooting (WBR) / 1.0 / 0.4 / 0.3 / 0.7 / 0.6 / -0.1 / 0.2 / 0.0 / -0.9 / -0.7 / 0.1 / 0.5 / 0.8 / 0.8 / 0.8 / 0.8 / 0.9
Altitude (h) / 1.0 / 0.4 / 0.5 / 0.6 / 0.6 / 0.0 / 0.1 / -0.4 / 0.0 / 0.6 / 0.5 / 0.5 / 0.5 / 0.6 / 0.4 / 0.3
Slope (Sl) / 1.0 / 0.2 / 0.3 / 0.6 / 0.1 / 0.6 / -0.1 / 0.0 / -0.1 / 0.6 / 0.2 / 0.3 / 0.3 / 0.5 / 0.3
Area (A) / 1.0 / 1.0 / 0.0 / 0.1 / -0.1 / -0.7 / -0.6 / 0.1 / 0.5 / 0.9 / 0.9 / 0.9 / 0.7 / 0.6
Perimeter (P) / 1.0 / 0.2 / 0.1 / 0.0 / -0.6 / -0.4 / 0.0 / 0.6 / 0.9 / 0.9 / 0.9 / 0.8 / 0.6
Herbivory (H) / 1.0 / 0.0 / 0.5 / 0.2 / 0.5 / 0.3 / 0.4 / 0.1 / 0.1 / 0.1 / 0.2 / -0.1
Jays (J) / 1.0 / 0.3 / 0.0 / 0.1 / 0.0 / 0.0 / 0.1 / 0.1 / 0.1 / 0.1 / 0.3
Acorn Production (AP) / 1.0 / 0.3 / 0.4 / -0.1 / 0.3 / -0.1 / -0.1 / 0.0 / 0.1 / 0.0
Ipatch (Ip) / 1.0 / 0.8 / -0.1 / -0.4 / -0.8 / -0.8 / -0.8 / -0.7 / -0.7
Imicroh (Im) / 1.0 / 0.2 / -0.2 / -0.6 / -0.6 / -0.6 / -0.5 / -0.5
UTMX (X) / 1.0 / -0.4 / 0.1 / 0.1 / 0.1 / -0.3 / -0.2
UTMY (y) / 1.0 / 0.5 / 0.5 / 0.6 / 0.9 / 0.6
Connectivity 0m (c0) / 1.0 / 1.0 / 1.0 / 0.8 / 0.8
Connectivity 1 m / 1.0 / 1.0 / 0.8 / 0.8
Connectivity 4m / 1.0 / 0.9 / 0.8
Connectivity 100m / 1.0 / 0.9
Connectivity 400m / 1.0
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Tables showing the step-by-step results while running the Structural Equation Modeling for each stage and a level. The last column (Paths) indicates paths that were excluded from the subsequent step by the previous-step model, starting with the saturated model. Abreviations: k, number of parameters of the model; AIC, Akaike Information Criterion; AICC, second order AIC; ∆AIC, AIC increment ; AICW, weighted AIC; Herb, herbivory; Paths, paths constrained to zero in each run; PSh, Patch shape; AP, acorn production per patch; WB, wild boars.
Table S2. a= 1, d= 0m - One-yr Seedlings
Model / k / ∆AICc / AICW / c2 / p-value / Paths1 / 54 / 215.667 / 0.000 / 777.44 / p < 0.0001 / Location -
Herbivory
2 / 53 / 193.315 / 0.000 / 581.59 / p < 0.0001 / PSh àWB
3 / 52 / 180.729 / 0.000 / 546.08 / p < 0.0001 / TopographyàRodents
4 / 51 / 170.972 / 0.000 / 541.911 / p < 0.0001 / PShà Rodents
5 / 50 / 161.684 / 0.000 / 529.79 / p < 0.0001 / PShà Seedlings
6 / 49 / 150.654 / 0.000 / 484.86 / p < 0.0001 / Connectivity àAP
7 / 48 / 132.638 / 0.000 / 312.66 / p < 0.0001 / PShàJays
8 / 43 / 94.332 / 0.000 / 221.46 / p < 0.0001 / PShàAP
9 / 42 / 80.950 / 0.000 / 85.92 / p < 0.001 / ConnectivityàWB
10 / 41 / 74.446 / 0.000 / 62.07 / 0.14 / Topographyà seedlings
11 / 40 / 71.675 / 0.000 / 102.76 / p < 0.0001 / LightàRodents
12 / 39 / 64.673 / 0.000 / 58.88 / 0.27 / APà WB
13 / 38 / 60.277 / 0.000 / 58.95 / 0.30 / Connectivityà Seedlings
14 / 37 / 56.117 / 0.000 / 58.94 / 0.33 / APà Seedlings
15 / 36 / 53.718 / 0.000 / 84.95 / 0.01 / Lightà WB
16 / 34 / 46.145 / 0.000 / 77.08 / 0.04 / Topographyà WB
17 / 28 / 27.231 / 0.000 / 50.58 / 0.08 / TopographyàJays
Topographyà AP
18 / 23 / 15.042 / 0.000 / 21.59 / 0.48 / WBà Seedlings
19 / 22 / 13.310 / 0.001 / 21.74 / 0.54 / Connectivityà Rodents
20 / 21 / 11.713 / 0.003 / 22.37 / 0.56 / Lightà Jays
21 / 20 / 9.676 / 0.007 / 15.79 / 0.54 / Connectivityà Jays
22 / 18 / 7.069 / 0.025 / 16.66 / 0.55 / APà Jays
23 / 17 / 4.559 / 0.089 / 16.15 / 0.18 / Jaysà Seedlings
24 / 13 / 0.000 / 0.874 / 13.24 / 0.10
Table S3. a= 1, d= 0m - Two-Yr Seedlings