Premium
HERBIVORE‐MEDIATED APPARENT COMPETITION BETWEEN TWO SALT MARSH FORBS
Author(s) -
Rand Tatyana A.
Publication year - 2003
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/0012-9658(2003)084[1517:hacbts]2.0.co;2
Subject(s) - herbivore , atriplex , biology , competition (biology) , ecology , salt marsh , plant tolerance to herbivory , forb , botany , grassland
Indirect negative interactions between prey species that share a predator, referred to as apparent competition, have been modeled extensively. However, experimental studies examining the importance of apparent competition in the field are sparse, especially in plant–herbivore systems. In this study, I examined the role of a beetle herbivore, Erynephala maritima , in mediating the indirect effects of an abundant host plant, Salicornia europaea , on a less common host species, Atriplex patula var. hastata , in New England salt marshes. To examine these relationships, I manipulated plant density (plants with vs. without neighbors) and composition (conspecific neighbors vs. Salicornia neighbors) surrounding focal Atriplex plants, as well as the presence or absence of herbivores in a field experiment. Densities of both beetle eggs and larvae were significantly greater in plots with Salicornia , suggesting that its presence increases patch location or selection by herbivores. Higher insect densities resulted in significantly higher levels of herbivore damage to Atriplex within Salicornia ‐addition plots compared with high‐ and low‐density Atriplex plots. Thus the identity, and not just density, of neighboring plants is important in determining levels of herbivory. Increased herbivore damage in Salicornia ‐addition plots resulted in a concomitant decrease in Atriplex survival and reproductive output. Furthermore, the negative effect of Salicornia on Atriplex survival and fruit production only occurred in the presence of herbivores, indicating that competitive effects are indirect rather than direct. Thus, Salicornia has a strong apparent competitive effect on Atriplex . Cross‐site surveys suggested that the pattern of increased herbivore damage to Atriplex associated with increases in local Salicornia density is common and widespread. Overall, the results suggest that the apparent competitive effect of Salicornia is likely a major determinant of patterns of Atriplex abundance both between habitat patches and across marsh zones. Corresponding Editor: D. Ayres.