Comparative Analyses of Herbivory Rates and Leaf Phenology in Invasive and Native Shrubs in an East-Central Indiana Forest1

Abstract

Exotic species that become invasive can have a strong impact on the success of native species because of traits that enhance their competitive abilities. This study investigates three potential trait differences between common invasive and native shrubs that could enhance the competitive success of invasives: resistance to herbivory, length of autumn leaf retention, and timing of spring leaf emergence. We measured herbivory per plant by leaf-chewing insects, autumn leaf color change and retention, and spring leaf-out in five native and five invasive shrub species in Wildman Woods near Richmond, Indiana, during the fall of 2014 and the spring of 2015. Although we found variation among species, native plants as a group had significantly greater percent leaf herbivory per plant compared to invasive plants, while invasive plants kept chlorophyll significantly later in autumn and had longer leaf retention. Invasive plants also leaf out slightly earlier than native species. Our findings in 2014 were very similar to previous unpublished work in the same area on several of the same species in 2002, 2004, and 2007, suggesting that these patterns are consistent between years. Overall, we found evidence that lower herbivory rates, longer leaf retention in fall, and perhaps earlier leaf-out in spring could improve the competitive abilities of invasive shrub species through increased season-long photosynthesis.

Adaptive associations among life history, reproductive traits, environment, and origin in the Wisconsin angiosperm flora

“…For example, if human disturbance provides an opening for introduced species, such species should be short in stature, short‐lived, and highly fecund, in order to succeed in regional competition (via enhanced dispersal) while losing in local competition for photosynthetic resources (Givnish, 1982b; Platt and Weis, 1985). But some introduced species may spread because they bear novel anti‐herbivore or anti‐pathogen defenses (Keane and Crawley, 2002; Mitchell and Power, 2003; DeWalt et al, 2004; Cappuccino and Carpenter, 2005; Bodawatta et al, 2019; but see Schultheis et al, 2015) or novel anti‐competitor weapons (Bais et al, 2003; Callaway and Ridenour, 2004; Rudrappa et al, 2007; Callaway et al, 2008; Lankau et al, 2009; Evans et al, 2016)—their success is tied not to disturbance but to eco‐evolutionary novelty per se (Simberloff et al, 2012; Seabloom et al, 2015). Many such species—like Rhamnus cathartica and Typha angustifolia —are tall, long‐lived, and/or woody, and thereby can succeed in local competition against native species for photosynthetic resources in less disturbed sites after their novel defenses or weapons give them an initial edge.…”

The Spontaneous Vascular Plant Flora of New York's Central Park11b

“…Some introduced ornamental plants may be preferred horticulturally because they are considered pest free, meaning that insects, fungi, and other herbivores do not exploit them as food or shelter. This is supported by a recent study showing that native plants have significantly greater leaf herbivory rates than introduced invasive species (Bodawatta et al 2019). A 1999 study showed that 96% of North American terrestrial birds rely on insects to feed their young (Tallamy 2007), but if the plants preferred by insects (native) are not there, the birds will suffer.…”