Fleshy fruit removal and nutritional composition of winter-fruiting plants: a comparison of non-native invasive and native species
Invasive, non-native plants threaten forest ecosystems by reducing native plant species richness and potentially altering ecosystem processes. Seed dispersal is critical for successful invasion and range expansion by non-native plants; dispersal is likely to be enhanced if they can successfully compete with native plants for disperser services. Fruit production by non-native plants during winter (or dormant season), when native fruits and arthropods are scarce, might enhance chances of fruit consumption and seed dispersal by vertebrates. We compared the proportion and rate of fruit removal among five invasive, non-native and two native plant species that retain fruit during winter to test whether non-native fruits are readily removed and their seeds dispersed by vertebrates–even where native fruit is available. We also assessed whether the nutritional content of fruit pulp affects fruit removal rates, and collected bird droppings from fecal traps to examine species and rates of seed dispersal. Most (83% to 93%) fruit was removed from all species except native Smilax rotundifolia L. (55%). Most (92%) seeds collected from bird droppings were from non-native plants (six species); only 8% were from native plants (four species). Mean fruit survival time (across species) was positively correlated with total sugar and negatively correlated with lipid. Total fruit consumed was not correlated with nutrient content. Our results indicate most fruits of tested winter-fruiting, non-native invasive plants are removed, and their seeds are dispersed. In the southern Appalachian Mountains, only a few native plant species, notably greenbriar (Smilax spp.), American holly (Ilex opaca Aiton), and sumac (Rhus spp.) retain abundant, ripe fruit during winter months, and these species tend to be patchy in their distribution. Therefore, winter fruit availability by non-native invasive plants offers an important opportunity for dispersal and range expansion, and is likely key in their successful invasion of ecosystems.