No abstract

In some spiders features of the webs of early instars may represent features of the ancestor's web. Some second instar spiderlings (first instar outside of the egg sac) of Tengella radiata (Kulczynski 1909) construct a small sheet web without any type of retreat. In subsequent instars, spiderlings construct webs that consist of a sheet with a small retreat that opens near its center. Webs gradually change as spiderlings growth and webs of 7 th instar spiders are indistinguishable from those of adult females. Spiders only begin to include cribellate threads in their webs during the 7 th instar. The growth of T. radiata is slow during the first three instars, but spiders' sizes increase steadily in the subsequent stages. Legs I of adult males are longer than in females, indicating an allometric growth that occurred mainly during the last molt of males.

In this paper, we describe the construction and function of the double sheet and tangle web of Tidarren sisyphoides (Walckenaer 1842). Web construction includes several stages: construction of the scaffolding that serves to support the rest of the web; filling in the dome-shaped and horizontal sheets; and construction of the upper tangle. During construction of the scaffolding, the spider descends by a pre-existing thread to the substrate, moves a few centimeters and attaches the dragline, then she ascends by the new thread, doubling the line or attaching it to another thread. The spider fills in the sheet while walking in an irregular pattern under the sheet, and attaching her dragline using either one or both legs IV simultaneously to hold pre-existing sheet lines against her spinnerets. During scaffolding construction and filling in the dome-shaped sheet, the spider returns frequently to the retreat, apparently using the same threads near the retreat each time. Threads of both the dome-shaped sheet and the horizontal sheet have small drops of viscid material. The domeshaped sheet and upper tangle comprise the functional trap of the web, while the horizontal sheet apparently plays only a little role in prey capture.

The Costa Rican Paramo is a unique ecosystem with high levels of endemism that is geographically isolated from the Andean Paramos. Paramo ecosystems occur above Montane Forests, below the permanent snow level, and their vegetation differs notably from that of adjacent Montane Forests. We compared the composition and beta diversity of blooming plant species using phenological data from functional plant groups (i.e., insect-visited, bird-visited and insect + bird-visited plants) between a Paramo and a Montane Forest site in Costa Rica and analyzed seasonal changes in blooming plant diversity between the rainy and dry seasons. Species richness was higher in the Montane Forest for all plant categories, except for insect-visited plants, which was higher in the Paramo. Beta diversity and blooming plant composition differed between both ecosystems and seasons. Differences in species richness and beta diversity between Paramo and the adjacent Montane Forest are likely the result of dispersal events that occurred during the last glacial period and subsequent isolation, as climate turned to tropical conditions after the Pleistocene, and to stressful abiotic conditions in the Paramo ecosystem that limit species establishment. Differences in blooming plant composition between both ecosystems and seasons are likely attributed to differential effects of climatic cues triggering the flowering events in each ecosystem, but phylogenetic conservatism cannot be discarded. Analyses of species composition and richness based on flowering phenology data are useful to evaluate potential floral resources for floral visitors (insects and birds) and how these resources change spatially and temporarily in endangered ecosystems such as the Paramo.