Effects of Environmental Salinity on Vertebrate Florivory and Wetland Communities

Abstract

Iris hexagona is a perennial freshwater species indigenous to Louisiana wetlands. Coastal iris populations that are exposed to saline conditions often suffer heavy floral browsing. This paper is the first to photographically document florivory by white-tailed deer (Odocoileus virginianus Zimmerman), which consume iris flowers and immature seed capsules. Severe florivory can prevent sexual reproduction in plants and eliminate habitat for floral arthropods. In this three-year study, we monitored environmental salinity, assessed natural levels of florivory, and established deer exclosures to test the effects of florivory on arthropod abundance and diversity. In two out of three years, florivory rates were positively correlated with the level of salinity at individual I. hexagona populations. In all three years, florivory in the brackish marsh was an order of magnitude greater than florivory in intermediate and freshwater sites. In 2003, the number and diversity of arthropods was significantly greater on unbrowsed (caged) than browsed (open) irises. In October 2002, Hurricane Lili struck our main study site, causing extensive damage to the landscape and heavy deer mortality. Despite this, floral browsing was high (88%) in spring 2003, and arthropod numbers and diversity declined significantly. Our results suggest that salinity may facilitate floral browsing, which can have direct effects on plant fitness and indirect consequences for arthropod communities in wetland plant populations.