Could poor seed dispersal contribute to predation by introduced rodents in a Hawaiian dry forest?

Abstract

Dry forests are among the most diverse, yet threatened, communities in Hawai'i. Dry forests throughout the archipelago suffer from a lack of natural regeneration of trees. Two factors that may limit tree recruitment include poor seed dispersal and seed predation by rodents. Poor or limited dispersal of fleshy-fruited species results in seeds and fruits falling directly under parents. Dispersed and nondispersed seeds may differ in their vulnerability to predation. We tested effects of seed location (under/ away from parent trees) and pulp (presence/absence) on predation of four native species that suffer from limited dispersal and one readily-dispersed alien species in Kanaio Natural Area Reserve, Maui. Three natives (Diospyros sandwicensis, Pleomele auwahiensis, Santalum ellipticum), had significantly more seeds removed under parent trees than in exposed sites away from trees. For the one alien (Bocconia frutescens) and two native trees (D. sandwicensis, P. auwahiensis) that were evaluated, significantly more intact fruits were removed than were cleaned seeds. Presence of teeth marks and gnawed seed husk fragments indicate introduced rodents are destroying many of the seeds they remove. These results suggest that seed predation is disproportionately concentrated among poorly-dispersed seeds and may contribute to recruitment failure.

Large-scale rodent control reduces pre- and post-dispersal seed predation of the endangered Hawaiian lobeliad, Cyanea superba subsp. superba (Campanulaceae)

“…Six of the 12 species had the majority ([50 %) of their fruit removed in treatments that were accessible to rats, and motion-sensing cameras also recorded only black rats removing fruit. Additional recent studies demonstrating post-dispersal fruit removal by invasive rodents have been conducted elsewhere in Hawaii (Chimera and Drake 2011) and in New Zealand (Moles and Drake 1999;Grant-Hoffman et al 2010a).…”

“…Rodents may also directly influence plants through the consumption of vegetative and reproductive parts (Sugihara 1997;McConkey et al 2003;Salvande et al 2006;Grant-Hoffman and Barboza 2010;Shiels 2011). As seed predators (see Grant-Hoffman and Barboza 2010 for a review), invasive rodents have been implicated in the breakdown of reproductive cycles of numerous island plant species (Campbell and Atkinson 2002;Meyer and Butaud 2009;Auld et al 2010;Chimera and Drake 2011;Shiels and Drake 2011).…”

“…In Hawaii, the majority of studies concerning the effects of introduced rodents on the native flora have only recently been conducted (Athens et al 2002;Pérez et al 2008;Shiels 2010;Chimera and Drake 2011;Shiels and Drake 2011). Rodents were absent from Hawaii prior to the introduction of the Pacific rat by Polynesian settlers approximately 800 years ago (Wilmshurst et al 2011).…”

Biology and Impacts of Pacific Island Invasive Species. 11.Rattus rattus,the Black Rat (Rodentia: Muridae)

“…Yamashita et al (2003) suggested that R. rattus may be facilitating the invasion of the nonnative tree Bischofia javanica in the Ogasawara Islands because R. rattus depredates the seeds of the dominant native tree Elaeocarpus photiniae-folius both before dispersal (27% -33% of the seed crop) and after dispersal (41% -100%). Several other studies of fruit and seed removal have occurred on Pacific islands that include R. rattus as part of the rodent community, but the particular rodent species responsible for such removals were not identified (e.g., Moles and Drake 1999, Uowolo and Denslow 2008, Meyer and Butaud 2009, Erwin and Young 2010, GrantHoffman et al 2010, Chimera and Drake 2011.…”

“…Rattus rattus does not seem to be limited by an upper temperature level, or at least this has not been investigated. Thus, R. rattus is abundant and spans most terrestrial communities, from arid lowland and montane ecosystems (Tamarin and Malecha 1971, Clark 1981, Amarasekare 1994, Harris and Macdonald 2007, Chimera and Drake 2011 to lowland and montane rain forests (Daniel 1973, Sugihara 1997, Lindsey et al 1999, Wegmann 2009). Even in highly disturbed environments, such as Eniwetok Atoll, which suffered numerous nuclear explosions, R. rattus survived in densities of approximately 20 individuals/ ha 10 yr after the last nuclear test (Fall et al 1971).…”