How plants affect amphibian populations

Descriptions of amphibian habitat, both aquatic and terrestrial, often include plants as characteristics but seldom is it understood whether and how those plants affect amphibian ecology. Understanding how plants affect amphibian populations is needed to develop strategies to combat declines of some amphibian populations. Using a systematic approach, we reviewed and synthesized available literature on the effects of plants on pond-breeding amphibians during the aquatic and terrestrial stages of their life cycle. Our review highlights that plant communities can strongly influence the distribution, abundance, and performance of amphibians in multiple direct and indirect ways. We found three broad themes of plants' influence on amphibians: plants can affect amphibians through effects on abiotic conditions including the thermal, hydric, and chemical aspects of an amphibian's environment; plants can have large effects on aquatic life stages through effects on resource quality and abundance; and plants can modify the nature and strength of interspecific interactions between amphibians and other species - notably predators. We synthesized insights gained from the literature to discuss how plant community management fits within efforts to manage amphibian populations and to guide future research efforts. While some topical areas are well researched, we found a general lack of mechanistic and trait-based work which is needed to advance our understanding of the drivers through which plants influence amphibian ecology. Our literature review reveals the substantial role that plants can have on amphibian ecology and the need for integrating plant and amphibian ecology to improve research and management outcomes for amphibians.

Timing of oviposition influences the effects of a non-native grass on amphibian development

Land-use change can alter the energy dynamics in aquatic systems by changing the subsidies that form the nutrient base within them. However, experimental evaluations of subsidy change often fail to consider how effects, such as differences in individual growth and survival, may differ under varying ecological contexts experienced in the field. We used a mesocosm approach to investigate how litter (Native Prairie or Non-Native Tall-Fescue Grass) surrounding wetlands and timing of oviposition affected larval amphibian development. We found that survival differed between litter types in the Early-Oviposition treatment, with nearly 100% mortality in Fescue treatments. Conversely, survival  was similar across litter types in the Late Oviposition treatment (~ 43%), and larvae in Late-Fescue treatments metamorphosed more quickly and were larger post-metamorphosis than larvae in Prairie treatments. Follow-up experiments confirmed that low dissolved oxygen (DO) was responsible for high mortality in Early-Fescue treatments; high quantities of Fescue resulted in a microbial bloom that reduced DO to < 2 mg/L for several days, resulting in low hatching success. This effect was eliminated in treatments with supplemental aeration. Finally, we confirmed that experimentally observed DO patterns also occurred in the field. Context (i.e., timing of inundation relative to amphibian breeding) is critical to understanding the effects of subsidies on amphibian populations; early and explosively breeding species may experience catastrophic mortality due to DO depletion; whereas, species that breed later may experience enhanced fitness of recruits. Considering the effects of non-native species across different ecological contexts is necessary for elucidating the extent of their impacts.

Synergistic effects of the invasive Chinese tallow (Triadica sebifera) and climate change on aquatic amphibian survival

Changes in climate and the introduction of invasive species are two major stressors to amphibians, although little is known about the interaction between these two factors with regard to impacts on amphibians. We focused our study on an invasive tree species, the Chinese tallow (Triadica sebifera), that annually sheds its leaves and produces leaf litter that is known to negatively impact aquatic amphibian survival. The purpose of our research was to determine whether the timing of leaf fall from Chinese tallow and the timing of amphibian breeding (determined by weather) influence survival of amphibian larvae. We simulated a range of winter weather scenarios, ranging from cold to warm, by altering the relative timing of when leaf litter and amphibian larvae were introduced into aquatic mesocosms. Our results indicate that amphibian larvae survival was greatly affected by the length of time Chinese tallow leaf litter decomposes in water prior to the introduction of the larvae. Larvae in treatments simulating warm winters (early amphibian breeding) were introduced to the mesocosms early in the aquatic decomposition process of the leaf litter and had significantly lower survival compared with cold winters (late amphibian breeding), likely due to significantly lower dissolved oxygen levels. Shifts to earlier breeding phenology, linked to warming climate, have already been observed in many amphibian taxa, and with most climate models predicting a significant warming trend over the next century, the trend toward earlier breeding should continue if not increase. Our results strongly suggest that a warming climate can interact with the effects of invasive plant species, in ways we have not previously considered, to reduce the survival of an already declining group of organisms.