| Where animals spend time can provide important clues to their ecological needs, but this information is very difficult to obtain for small volant animals. The research described in Chapter 1 was an attempt to discern how L. nivalis utilize the landscape in relation to the distribution of Agave havardiana in Big Bend National Park, Texas. I found that although the landscape use of Leptonycteris nivalis is centered on habitat with high concentrations of blooming A.havardiana, it is not restricted to those areas, and furthermore adults and juveniles may differ in their behavior. Adult females may remain near food sources in order to replenish energy stores lost to migration and the demands of reproduction, whereas juveniles may feed early in the evening and then undertake occasional far-reaching expeditions, perhaps in order to create a navigational map. If this behavior is widespread among juveniles, it emphasizes the need to carefully assess the risk of constructing wind-turbine energy facilities not just within agave-rich habitat, but anywhere near the range of this endangered bat species.;The research described in Chapter 2 focused on documenting the importance of flowering agaves as a food resource for the many vertebrate and invertebrate, diurnal and nocturnal visitors. I found that A. palmeri was visited by a wide variety of vertebrate and invertebrate visitors, many of which are pollinators of other plants, and that there was considerable variation in visitation rates in space and time -- in fact, bats were not even observed at one of the study sites. Increased visitation was associated with larger plant sizes for all visitor types assessed.;In Chapter 3, I explored how the fruit and seed production of A. palmeri at these three sites were affected by the plants' morphology, phenology (timing of bloom), prior reproductive success, and the patterns of visitation by different animal guilds. Models indicated that bats were the most effective visitors, because periods with high bat visitation rates also had very high seed. Periods with high bird visitation resulted in many fruits but with poor seed set, possibly indicating that they are responsible for some degree of reproduction, though the exact mechanism is not clear. Floral branch position interacted in a complex manner with prior fruit set, affecting fruit set, seed set, and mean seed mass. Plants with high prior fruit set showed decreased seed set in fruits on late-blooming branches, possibly indicative of resource limitation. |
