Distribution of Plants with Extrofloral Nectaries and Ants at Two Elevations in Jamaica

Abstract

Frequencies of plants with extrafloral nectaries were determined for two elevations in Jamaica. Extrafloral nectaries were found on 0.28 of the plants at sea level (Happy Grove, Portland) and 0.00 of the plants at 1310 m (Whitfield Hall, St. Thomas). Ant abundance, as indicated by discovery of and recruitment to baits, was greater at the lower elevation site. However, despite the apparent absence of plants with extrafloral nectaries, there were abundant ants at 1310 m. MUCH EVIDENCE suggests that extrafloral nectaries attract insects which defend plants against herbivores and/or seed predators (Elias and Gelband 1975; Bentley 1976, 1977a, b; Keeler 1977). Extrafloral nectaries are glands which are located anywhere on a plant except those sites involved in pollination. These glands produce an aqueous solution containing sugars and other compounds (Baker and Baker 1975, Bentley 1977a, Keeler 1977). At present, only Bentley (1976) has studied the distribution of extrafloral nectaries in a natural habitat. She reported a positive correlation between frequency of plants with extrafloral nectaries and ant abundance in tropical dry forest in Guanacaste, Costa Rica. I report extrafloral nectary frequency and ant abundance from two sites in Jamaica. Two sites were compared: Happy Grove, Portland, Jamaica (sea level, approximately 1700 mm annual rainfall, mean annual temperature 260C, mean monthly temperatures 24-28?), and Whitfield Hall, near Hagley Gap, St. Thomas (1310 m up Blue Mountain, 3500 mm annual rainfall, mean annual temperature 220 C, mean monthly temperatures 16-32?). Since there are no weather records for the specific sites, values are extrapolated from U.S. Weather Bureau (1966) and Clarke (1974). Significant human disturbance was seen at both sites. Studies were conducted close to trails used daily by local people. The transects at both sites ran from under the forest canopy (presumably second growth) out into partially open areas (early second growth at Happy Grove, coffee fields at Whitfield Hall). Frequency of plants with extrafloral nectaries was determined in four transects at each site. At approximately every meter along each transect, plants were scored as having or lacking extrafloral nectaries and ants. The presence of extrafloral nectaries was determined by observing ants feeding in a stereotyped manner, and then locating the nectary. Once a species was determined to have extrafloral nectaries, it was scored as such on subsequent encounters. Ants were present at most extrafloral nectaries; of the 70 plants with extrafloral nectaries observed, only 10 (14%) did not have ants on them. The frequency of plants with extrafloral nectaries determined by this method is an underestimate, since some species may produce extrafloral nectar at other times of the year (e.g., fruit nectaries). Ant abundances were estimated by using baits of canned corned beef and local commercial jelly. A pile of each food about 1 cm in diameter was placed on a separate piece of plastic, 25 cm2, in the litter at each station. Time until arrival of the first ant, type of ant, peak number of ants responding and number of ant species attracted were recorded at each bait. Representative ants from baits at both sites and from foliar nectaries of plants at Happy Grove were collected. The experiments were carried out for three hours each, from 09.00-12.00 hrs in December 1977. Results from the extrafloral nectary transects are given in table 1. No species with extrafloral nectaries was observed at Whitfield Hall. At Happy Grove, 28 percent of the observed plants had extrafloral nectaries. These differences are statistically significant (T-test; p p> 0.01 and p-0.005, respectively). Ants collected from baits at Hatpy Grove included Paratrechina longicornis (Latreille), Solenopsis sp. 152 BIOTROPICA 11 (2): 152-154 1979 This content downloaded from 207.46.13.75 on Fri, 08 Jul 2016 05:47:31 UTC All use subject to http://about.jstor.org/terms (not S. geminata) , and Tetramorium guineense (F.); ants collected at Whitfield Hall were P. longicornis, Crematogaster brevispinosa Mayr., and Monomorium floricola (Jerdon). Ants collected from extrafloral nectaries at Happy Grove were P. longicornis, Solenopsis sp. (same as above), and Wassmannia auro-