A Temperate Region Plant‐Ant‐Seed Predator System: Consequences of Extra Floral Nectar Secretion by Helianthella Quinquenervis

Abstract

Helianthella quinquenervis (Asteraceae), the aspen sunflower, secretes sugar and amino acid rich nectar from involucral bracts during bud and flowering stages. The nectar is usually collected by ants as fast as it is secreted. H. quinquenervis is subject to predispersal seed predation by larvae of several insect species, primarily tephritid flies, an agromyzid fly, and 3 Lepidoptera. When present, ants interrupt oviposition efforts by the female flies but do not appear to be effective against lepidopteran or mammalian herbivores. The degree of protection by ants conferred upon plants was investigated by excluding ants from some plants and by correlating ant density with subsequent damage to ovules and developing seeds. At higher elevations (2896 and 3091 m) damage to plants with ants was significantly reduced compared with plants without ants. At a lower elevation (2734 m) where seed predator and ant densities were highest, the ants were less effective as deterrents and predation on ovules and seeds usually exceeded 60%. Flowers of some other composite species in the same habitats appear to be more effectively protected from predation by chemical deterrents, raising questions of the relative benefits of chemical deterrents compared to ants as a means of protection.

Recruitment of predators and parasitoids by herbivore-injured plants

“…The benefit of extrafloral nectar production to plant fitness has been well established (Bentley, 1977;Inouye and Taylor, 1979;O'Dowd, 1979;Wagner, 1997;Koptur et al, 1998). Whether induction further enhances plant fitness over constitutive nectar production remains an open issue.…”

Extrafloral Nectaries on Plants in Communities without Ants: Hawaii

“…The interaction of plants with their nectarfeeders has been shown to be a mutualistic antiherbivore defense: ants exclude or prey upon herbivores while visiting extrafloral nectaries (e.g. Bentley 1977, Tilman 1978, Inouye and Taylor 1979, Keeler 1980b, Schemske 1980, Beckmann and Stucky 1981, Stephenson 1982, but see also O'Dowd and Catchpole 1983, and Tempel 1983 for counter-examples).…”

Distribution of Plants with Extrafloral Nectaries in Temperate Communities

“…Certainly distinct seasonality is suggested for the EFNs of Prunus ser?tina (Tilman, 1978) and Helianthella quinquenervis (Inouye and Taylor, 1979). The other temperate species studied in the literature, Campsis radicans (Elias and Gelband, 1975), has a series of EFNs which probably maintain nectar production throughout the growing season.…”

“…Therefore, the distribution of EFNs should be related to the distribution of ants. Most studies support ant-plant mutualism (Elias and Gelband, 1975;Bentley, 1976Bentley, , 1977bKeeler, 1977Keeler, , 1980Deuth, 1977;Tilman, 1978;Inouye and Taylor, 1979;Pickett and Clark, 1979).…”

“…Available studies have shown EFN visitors to provide protection to the plant from damage, including flowerrobbing (Elias and Gelband, 1975;Keeler, 1977), seed loss (Bentley, 1977b;Deuth, 1977;Inouye and Taylor, 1979;Keeler, 1980;Pickett and Clark, 1979) and leaf damage (Keeler, 1977;Tilman, 1978). Bentley (1977a) reviewed the literature regarding protection of plants by EFNs. Little is known about the distribution and abundance of plants with EFNs.…”