Detritus Quality and Locality Determines Survival and Mass, but Not Export, of Wood Frogs at Metamorphosis

Abstract

Single-site experiments have demonstrated detritus quality in wetlands can have strongly negative, neutral, and even positive influences on wildlife. However, an examination of the influence of detritus quality across several regions is lacking and can provide information on whether impacts from variation in detritus quality are consistent across species with wide ranges. To address this gap in regional studies we examined effects of emergent and allochthonous detritus of different nutrient qualities on amphibians and assessed a mechanism that may contribute to potential impacts. We used aquatic mesocosms to raise wood frogs (Rana sylvatica) from two regions of the United States with whole plants from purple loosestrife (Lythrum salicaria), leaf litter from native hardwood trees, and a mixture of both. We examined several metrics of amphibian fitness and life history, including survival, number of days to metamorphosis, and size at metamorphosis. Further, we quantified whether the effects of detritus type could translate to variation in anuran biomass or standing stock of nitrogen or phosphorus export. Our results show detritus with high nutrient quality (purple loosestrife) negatively influenced survival of wood frogs, but increased size of metamorphic individuals in two different regions of the United States. Despite the decrease in survival, the increase in size of post-metamorphic anurans raised with high quality detritus resulted in anuran biomass and standing stock of N and P export being similar across treatments at both locations. These results further demonstrate the role of plant quality in shaping wetland ecosystem dynamics, and represent the first demonstration that effects are consistent within species across ecoregional boundaries.

Stable isotopes reveal an invasive plant contributes more than native sources to anuran larvae diets

“…Nevertheless, purple loosestrife is known to decrease survival of larval anurans due to a high concentration of secondary compounds Brown et al 2006). Foraging theory states that organisms will make dietary choices that will increase their fitness, but frog species in this study chose to consume plant matter that is decreasing their survival rates suggesting other factors could be influencing their choices (Barrett et al Forthcoming;Pyke 1984;Milanovich et al 2016). …”

“…If tadpoles are choosing to consume purple loosestrife because of false environmental cues and their survival and fitness are decreasing due to that choice, then purple loosestrife invasions create putative ecological traps (Barrett et al Forthcoming;Battin 2004;Maerz et al 2005;Brown et al 2006;Milanovich et al 2016). An ecological trap can arise when an organism chooses a maladaptive habitat due to false environmental cues that leads to a decline in reproductive fitness and/or survival (Battin 2004;Robertson & Hutto 2006;Gilroy & Sutherland 2007).…”

“…Invasion of purple loosestrife (L. salicaria) introduces a nutrient-rich food source (Milanovich et al 2016) with higher concentrations of secondary compounds (Rauha et al 2001) to wetland ecosystems as a potential food source for tadpoles. Tadpoles need to consume a highly nutritious diet to prepare for and complete metamorphosis, which could be attracting tadpoles to choose purple loosestrife as part of their optimal diet (Kupferberg 1997).…”

“…Tadpoles need to consume a highly nutritious diet to prepare for and complete metamorphosis, which could be attracting tadpoles to choose purple loosestrife as part of their optimal diet (Kupferberg 1997). Foraging theory implies that tadpole fitness will increase when consuming optimal diets (Pyke 1984;Searle et al 2005); however, the consumption and presence of purple loosestrife has been shown to decrease tadpole survivorship (Barrett et al Forthcoming;Brown et al 2006;Cohen et al 2012;Milanovich et al 2016). Tadpoles exposed to higher concentrations of secondary compounds associated with purple loosestrife experienced changes to metamorph size and duration of the development period (Cohen et al 2012;Milanovich et al 2016).…”

“…Foraging theory implies that tadpole fitness will increase when consuming optimal diets (Pyke 1984;Searle et al 2005); however, the consumption and presence of purple loosestrife has been shown to decrease tadpole survivorship (Barrett et al Forthcoming;Brown et al 2006;Cohen et al 2012;Milanovich et al 2016). Tadpoles exposed to higher concentrations of secondary compounds associated with purple loosestrife experienced changes to metamorph size and duration of the development period (Cohen et al 2012;Milanovich et al 2016). Within wetlands invaded by purple loosestrife, tadpoles are presented with a choice between consuming an invasive plant that is more nutritious, but toxic, or native plants that do not have the same quality of nutrients.…”