Spatial Variation in the Strength of a Trophic Cascade InvolvingRuellia nudiflora(Acanthaceae), an Insect Seed Predator and Associated Parasitoid Fauna in Mexico

Abstract

Spatial variation in the strength of herbivore top-down control represents an important source of variation in plant fitness measures and community structure and function. By measuring seed predator (larvae of a Noctuid moth) and parasitoid impacts on Ruellia nudiflora across a broad spatial scale in Yucatan (Mexico), this study addressed the following: (1) to what extent does seed predator and parasitoid attack intensity associated with R. nudiflora vary spatially? (2) Does parasitoid attack result in a positive indirect effect on the plant, and does the intensity of this effect vary spatially? During the peak of fruit production (late June-early July) of 2005, we collected fruits from 21 R. nudiflora populations and grouped them into four regions: center, east, north and south. For each fruit we recorded: observed seed number, number of seeds eaten, seed predator presence, parasitoid presence and number of seeds 'saved' by parasitoids. Seed predators attacked ca 30 percent of fruits/plant on average, while parasitoids were found in 24 percent of seed predator-attacked fruits. Results indicated spatial variation in seed predator and parasitoid attack levels; interestingly, a contrasting spatial gradient of attack intensity was observed: populations/regions with greatest parasitoid attack levels usually had the lowest seed predator attack levels and vice versa, suggesting top-down control of parasitoids on seed predators. We observed a weak overall indirect impact of parasitoids on R. nudiflora (4% seeds 'saved' on average), which nonetheless varied strongly across populations (e.g., close to 14% seeds saved at one population). Findings indicate a geographical structuring of interaction strengths across populations, as well as spatial variation in the strength of parasitoid cascading effects on plant reproduction. Abstract in Spanish is available at

Ecological and evolutionary consequences of plant genotype diversity in a tri‐trophic system

“…(Acanthaceae) is distributed from Texas (USA) to Honduras (Long 1977), and in Yucata´n (southeast Me´xico) it grows across a wide range of abiotic conditions (Ortego´n-Campos et al 2012). Although evidence thus far suggests that only one seed predator species is present in this system (based on sampling from more than 20 populations [Abdala-Roberts et al 2010]), the possibility of having cryptic species cannot be discarded. Chasmogamous flowers may also self-pollinate autonomously upon corolla dehiscence when anthers come into contact with the stigma (Abdala-Roberts et al 2014).…”

“…Chasmogamous flowers are found on vertical inflorescence stalks that are 20-30 cm in height, while CL flowers are usually produced on lateral inflorescences at the base of the plant. Parasitoids stop or reduce seed predator consumption, thus having an indirect positive effect on plant fitness through this so-called seed ''rescue'' effect (Abdala-Roberts et al 2010). Although evidence thus far suggests that only one seed predator species is present in this system (based on sampling from more than 20 populations [Abdala-Roberts et al 2010]), the possibility of having cryptic species cannot be discarded.…”

“…Its fruits are attacked by larvae of a seed-eating moth, which in turn is parasitized by several species of wasps that reduce herbivore seed consumption (Abdala-Roberts et al 2010; see Plate 1). Its fruits are attacked by larvae of a seed-eating moth, which in turn is parasitized by several species of wasps that reduce herbivore seed consumption (Abdala-Roberts et al 2010; see Plate 1).…”

Influence of multiple factors on plant local adaptation: soil type and folivore effects in Ruellia nudiflora (Acanthaceae)

“…B3 km away) in order to achieve a sufficiently large number of seeds to conduct the experiment. Biotic and abiotic conditions were homogeneous between locations at each site (Abdala-Roberts et al 2010).…”

“…A previous study found that R. nudiflora was not locally adapted in terms of fitness-related traits, but that folivores have a significant effect on its reproductive output (Ortegón-Campos et al 2009). In addition, although damage by other insect herbivore guilds has been shown to vary significantly between populations, it has shown to remain relatively constant between years within a given site (Abdala-Roberts et al 2010). On the other hand, R. nudiflora populations are found on different soil types which vary in pH, fertility and depth (Bautista et al 2007).…”