In this paper, the spatial occurrence of seeds of pioneer species, a well-defined guild in cloud forest at Monteverde, Costa Rica was examined. Sampling for the study was concentrated along 5 transects, each 500 m long, through pristine lower mountain wet forest and lower mountain rain forest. Results showed that Monteverde soils contain high but variable densities of dormant seeds like most tropical soils. Overall densities (i.e., all species, including those with seasonal and transient seed as well as those which are persistent) ranged from 3000 to over 6000 m-2; the typical 25×25 cm sample contained 20-25 species.
We present evidence that differences in soil seedbank persistence among pioneer plants in the cloud forest of Monteverde, Costa Rica, are influenced by differences in seed chemical defense. We used extracted seed chemicals from Bocconia frutescens (Papaveraceae), Guettarda poasana (Rubiaceae), Phytolacca rivinoides (Phytolaccaceae), Urera elata (Urticaceae), Cecropia polyphlebia (Cecropiaceae), and Witheringia meiantha (Solanaceae) to assess seed chemical defense in two ways: (1) a plant pathogen inhibition assay using Pythium irregulare; and (2) a brine shrimp toxicity assay using Artemia salina. The combined performance of each species in the two assays positively correlated with seedbank persistence. In the pathogen assay, mycelium growth was reduced when Pythium was cultured on media containing seed extracts from the three species with the greatest seed longevity in the soil (i.e., Bocconia, Guettarda, and Phytolacca). Bocconia, the most persistent species, was the only species that contained chemicals toxic to brine shrimp, an indication of defense against arthropods. We focused on Bocconia defense by isolating the chemicals toxic to brine shrimp and identified them as dihydrosanguinarine, dihydrochelirubine, and dihydrochelerthrine. We found these alkaloids in Bocconia seeds at much higher concentrations (∼50 mg/g seed material) than in leaves. These chemicals are likely responsible for the exceptional longevity of Bocconia seeds in the soil. Phytolacca and Guettarda seeds also remain viable in the soil for long periods probably due to antipathogen chemicals detected in our analyses. In contrast, the species that do not persist (i.e., Urera, Cecropia, and Witheringia) lacked seed defensive chemicals in our assays.Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp.
Recent studies of attraction to sodium chloride baits suggest that diverse ant species forage for salt. We used experimental presentations of salt baits to test whether leaf cutter ants (Atta cephalotes) are attracted to and harvest salt-treated paper baits that offer no other resources. Atta foragers were most attracted to sucrose baits (positive control), but more foragers touched and cut salt-treated baits than water-treated baits (negative control). Furthermore, the ants removed more paper from the salt baits than from water-treated baits. We conclude that leaf cutter ants expend time and energy to harvest salt in the absence of other rewards. Salt could be harvested for the workers' consumption, or it could be fed to the fungus gardens in the ants' nest.
Males of the weevilParisoschoenus expositususe their prothoracic horns as weapons in stylized battles with other males over females that are drilling oviposition holes in palm leaves. The unusual sheath-like structures that penetrate deep into the male prothorax function to receive the horns of opponents during battles. Horn size is dimorphic with respect to body size, and small and large males also differ behaviorally. Small males that have mated with a drilling female are sometimes able to impede a large male's access to the female until after she has oviposited, but they are not able to take over females from larger males.
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