Does the seed disperser matter? The influence of dispersal type on survival of Araucaria angustifolia seeds


 Zoochoric dispersion is fundamental for the colonization of habitats by plants with large and heavy seeds such as the Paraná pine (Araucaria angustifolia). This is an endangered conifer from South America whose recruitment is heavily impacted by animals, but the way that different zoochoric dispersal modes and deposition sites can affect its successful establishment is not known yet. Thus, in this study, we aimed to evaluate the effect of dispersal mode (accordingly to the seed disperser), distance from adult conspecifics, and disposition site on long-term recruitment success. The experimental design included two environments (forest and open field) and each of them received 30 micro-habitat sampling stations (simulating deposition sites: 10 under conspecific; 10 far from conspecifics, next to a landmark; and 10 far from conspecifics, without a landmark), and each microhabitat had three levels of dispersal type simulating animal treatment (intact buried seed; intact seed over the ground; partially preyed seed over the ground), each with five seeds, totaling 900 seeds. In the forest environment, an experiment was also conducted to verify the fate of seeds using the spool and line technique. The environment and the micro-habitat alone did not explain seed survival, although the dispersal type given by the animal disperser was significant for survival and the buried seeds were the only ones that survived until the last survey. With the spool and line seed experiment, we attested that most of the Paraná pine seeds were preyed after removal (81.5%), and only buried seeds survived, reinforcing the role of scatter-hoarding animals as important agents in the Paraná pine dispersal. This way, our results showed that Paraná pine seeds suffer a very high predation rate, and that only a few seeds escape from predators and recruiting (only 1.1% of the all seeds used in the two experiments), indicating that the survival of seeds is a critical step in the life cycle of this plant, highlighting the role of dispersal mode in recruiting success.


70
According to the Janzel-Connell model the likelihood of seed survival is higher far from conspecific 71 adults, but this model is mainly applied when the predators are invertebrates (Janzen 1970;Connell 1971

77
Zoochoric dispersal occurs between 50% to 90% of tropical tree species, evidencing animals' importance 78 for plant recruitment (Francisco and Galetti 2001). Among the most singular forms of zoochoric dispersers are the 79 scatter-hoarding animals (synzoochory), which are seed predators that commonly store seeds in branches or under 80 the ground to survive periodic shortages of food (Smith and Reichman 1984;Vander Wall 2001). However, some 81 of the hidden seeds end up not being recovered, presenting high germination rates since they are protected from 82 desiccation, freezing, fire, pests, and predators (Forget 1990; Kollmann

84
Scatter-hoarding mammals and birds usually store the seeds near logs, shrubs, and tree trunks (Pons and  , and this process was verified for the Araucaria Forest, whose main element is the Paraná pine 92 (Araucaria angustifolia) and has expanded into pasture environments (Hueck 1953;Carlucci et al. 2011b).

93
The seed maturation of the Paraná pine occurs primarily in Austral Autumn and Winter (Mattos 2011) 94 and this species is considered a key species, providing food for the regional fauna (

104
There are two ways that the Paraná pine seed dispersal occurs, the first, when a predator accidentally

113
In consequence, some studies focusing on the Paraná pine's seed dispersal were limited to evaluating only the first 114 path of the predation and removal process, without monitoring the seeds until their final destination (e.g. Iob and

122
Acknowledging the importance of dispersal aspects for several critical ecology issues (Schupp et al. Table S5). The stations were located at least 30 meters from the other, a distance considered sufficient for sampling

205
The seeds were selected using the floating technique (floating seeds were discarded) and by the visual 206 inspection (larvae infestation) to attest germination viability (Doni Filho et al. 1985). We placed the seeds in the

220
In the trial to evaluate the effects of the environment, micro-habitat, and type of dispersion, on the survival 221 of unmarked seeds, the complete three-factor RM-ANOVA was used for interactions up to third order. In the assay 222 with marked and unmarked seeds in the different treatments, survival was evaluated with complete two-factor RM-

223
ANOVA for interactions up to second order. The latter was also used to evaluate the effects of the types of 224 dispersers and micro-habitat on the survival of marked seeds.

226
Effects of the environment, micro-habitat, and dispersal type

227
In the first experiment (unmarked seeds), from 900 seeds used to assess the effects of the environment, 228 micro-habitat, and dispersal type, 11.8% were predated on the initial position site (FT=11.5% in and OP=12%),

236
The micro-habitat (seed dispersal site), as well as the environment, did not explain the seed survival alone 237 (F=0.67, p=0.51). On the other hand, the dispersal type provided by the disperser was significant for survival 238 (F=10.87, p<0.001), and the buried seeds were the only ones that survived until the last survey (Fig. 3). In the open 239 field (OF) area, buried seeds (IB) far from conspecific adults and next to a landmark (NL) (n=50) presented 8% of 9 germination, which is equivalent to 0.88% of all seeds in this environment (n=450), or 0.44% of the total (n=900).

241
Still, 4% of OF-NL-IB seeds (initial n=50) and 2% of OF-UC-IB (n=50) remained possibly viable, but they did 242 not germinate, totaling 0.66% of the seeds in open fields (n=450), or 0.33% of all seeds (n=900). This resulted in 243 a significant interaction between environment and micro-habitat (F=3.78, p=0.02), indicating that seeds in open 244 fields, far from conspecific adults, and next to landmarks are more likely to survive.

245
The highest animal-seed interaction rates occurred in the first survey, after 30 days of initial disposal, 246 with 89.5% of the total, when the largest number of seeds were removed and predated, both in the open field (OF 247 = 88.6%) and in forest (FT=90.6%), which resulted in a significant response for the time factor (

261
The Paraná pine seeds marked with spool and line followed the same pattern as the unmarked seeds,

262
having the highest interaction rates with animals during the first survey (30 days after the placement of the seeds).

263
In this phase, 64.9% of seeds were predated, while 8.8% were stocked, 14% had not been removed from the 264 disposal sites, and 12.2% were removed, but due to line breakage it was not possible to reach the destination. Up 265 to the last survey 81.5% of the seeds had been predated and 14.6% were removed but lost due to broken lines (Fig.   266   4).

267
There was only one secondary storage in the 60-day survey, without storage in the other reads and, 268 therefore, the number of stored seeds did not change from the first survey to the others. The average distance of 269 the storage locations in relation to the initial position of the seeds was only 2.81 m, ranging from zero (buried in 270 the initial position) to 13.8 m.

271
Intact buried seeds (IB) in their initial position were the only ones to germinate, that occurred in the third 272 and fourth surveys (90 and 120 days respectively), representing 1.33% of the total, although just 0.88% survived 273 until the end of the experiment (SI , Table S4). Possibly viable Paraná pine seeds that had not germinated yet totaled 274 1.77%, mostly corresponding to intact buried seeds (IB= 1.54%), and only one seed (0.22%) removed and stored 275 by an animal. Some seeds also had mortality linked to other causes, such as dehydration and rot, totaling 1.11%.

276
From the predated seeds the main responsibles were the Plush-crested jays (Cyanocorax chrysops) 277 (39.56% of the seeds), small rodents (22.67%), the green agouti (Dasyprocta azarae) (16%), and insects attacked 278 1.33% of seeds (SI, Fig. S3).    (Forget 1990;Kollmann and Schill 1996), demonstrating the 301 importance of the relationship between scatter-hoarding animals and the Paraná pine. Despite that, the spool and 302 line experiment revealed that only 0.2% of the seeds stored by animals (9,1%) survived to secondary dispersal 303 during the experiment. Overall, plants that are dispersed by scatter-hoarding animals suffer high seed predation 304 rates, as evidenced for Bertholletia excelsa, with scatter-hoarding rodent recovery up to 99.4% of cached seeds 305 (Haugaasen et al. 2010). In another example, for Carapa procera, a tropical tree that is also dispersed by scatter-306 hoarding animals, the establishment of seedlings was less than 1% of the seeds available to the animals, ranging 307 from 0.7%, in a year of high seed production, to only 0.1% in low production years (Jansen et al. 2004). Most

314
On the other hand, seeds left above the ground did not present survival. Partially predated seeds,

322
The micro-habitat, which represented sites where seeds may be dispersed, did not explain survival alone,

334
In the OF, the greatest survival was observed in seeds far from conspecific adult next to landmark,            390 Table 1 Results of classical repeated-measure of three-factor analysis of variance for Paraná pine seed survival 569 (data transformed into arcsine square root). The test statistics () and probabilities obtained by the corrective 570 procedures for sphericity of Geisser and Greenhouse (1958) and Huynh and Feldt (1976)