Inflorescence size and butterfly visitation in Lantana camara ( Verbenaceae )

Pollinators greatly influence the fitness of most tropical plants, and how effective plants are at attracting pollinators is key to their success. This investigation focuses on how inflorescence size of Lantana camara affects butterfly visitation. Naturally occurring inflorescence size was determined by counting how many flowers per inflorescence and how many inflorescences were in bloom per branch. The average number of flowers per inflorescence is 37 and the average number of inflorescences in bloom per branch is 2. To assess the impact of inflorescence size on butterfly visitation, five different sizes of L. camara inflorescences were created by bundling from one to five inflorescences, ranging from an average of 36 to 208 flowers per bundle. Butterfly visitation to each of these was recorded during sunny periods in the Monteverde Butterfly Garden, Monteverde, Costa Rica. As the size of the inflorescence increased, so did butterfly visitation. However, the proportion of butterfly visitors to number of flowers decreased as inflorescence size increased. Other traits (morphology, plant vigor, scent, etc.) impact attractiveness to butterflies. What is the point of the previous sentence? The interaction and balance of these other traits along with inflorescence size would reveal interesting results about how angiosperms create attractive inflorescences. ___________________________________________________________________________ Animal-mediated pollination in the Tropics defines a plant’s fitness, as species are normally rare and widely spaced. These tropical plants depend on insects for effective pollination. Over 90% of tropical plants rely on animals for pollination. Because plant species are generally rare and widely spaced, pollination is less likely. Therefore flowers have to be noticeable and attractive. To a pollinator, the attractiveness and pollination of a plant species generally depends on the characteristics of both the individual flower and how they are displayed in an inflorescence (Harder et al. 2004). Visual traits, such as bright red or orange color common sources of attraction for many pollinators, especially butterflies (Faegri et al. 1979, Lewis et al. 1990). Flowers are also able to increase their attractiveness using odor, reward and size (Stebbins 1970). One way of increasing reward and flower size is by increasing the number of flowers per inflorescence. Inflorescences can be groupings of smaller flowers that can vary greatly in floral number. Flowers are expensive for plants to produce and for lowland tropical plants where the average floral lifetime is just one day. Therefore, the greater energy expense of larger inflorescences should translate into more visits by pollinators. It is possible that the number of visits could be additive, or larger inflorescences may mean a disproportionate increase of visits. In the latter case, natural selection should favor larger inflorescences, as a small increase in floral number increases the benefit greatly. Past studies have shown that plants with large floral displays attract more pollinators than plants with only a few open flowers (Eckhart 1991). In one such study, bumblebees responded strongly to floral display size and generally preferred plants with numerous flowers (Mitchell et al. 2004). With a larger inflorescence size, the size of the landing platform and the quantity of reward are increased, both contributing to the flower’s attractiveness (Ohashi et al. 2001, Scheske 1976). This study focuses on the common species Lantana camara (Verbenaceae). L. camara has a varying number of inflorescences of the same age located at each of its nodes. Each of these inflorescences has a varying number of bracteates, sessile dioecious flowers arranged spirally that develop from the center to the periphery (Knuth 1905, Mathur et al. 1986). Like many other tropical plants, they are insect pollinated, most commonly by butterflies (Faegri et al. 1979). This study investigates some of the naturally occurring characteristics of L. camara as well how butterfly visitation is effected through the manipulation of inflorescence size, from naturally occurring to larger sizes. MATERIALS AND METHODS This experiment was conducted at the Jardín de Mariposas (Butterfly Garden) located in Monteverde, Costa Rica, a lower montane wet forest. The Butterfly Garden consisits of four different gardens of varying size and each contained different varieties of butterflies. The garden used in this study is approximately 20 feet by 30 feet, fitted with plants that are naturally occurring in Costa Rica, and is covered with a roof allowing sun to enter, but does not allow for direct sunlight. Flowers Per Inflorescence: To determine the naturally occurring number of flowers per inflorescence, the number of flowers per inflorescence of 100 L. camara inflorescences was recorded. This data was then added and averaged. Although only yellow flowers present a reward (Scheske 1976, Mathur et al. 1986), the combination of red, orange and yellow colors plays a role in attractiveness for butterflies (Faegri et al. 1979, Lewis et al. 1990), so all flower colors were counted when taking samples.