Mid- and Long-Term Effects of Wildfire and Debris Flows on Stream Ecosystem Metabolism

Wildfire is an important and prevalent agent of disturbance in vegetated landscapes across much of the Earth’s surface, including forested watersheds in the arid western USA. Between 1992 and 2003, \u3e40% of the watersheds in the upper reaches of the Boise River watershed in central Idaho burned. The purpose of our study was to investigate the legacy effects of wildfire on stream ecosystems by analyzing the relationship between wildfire and resulting debris flows and their joint effects on stream ecosystem metabolism in 31 streams. The watersheds of ∼½ of these streams burned within the last 11 y, and some of these burned watersheds also experienced large-scale debris flows 1 y postfire. Streams with burned watersheds recovered quickly, and estimates of photosynthetically active radiation, gross primary production, and ecosystem respiration were indistinguishable from those in streams draining unburned watersheds. However, streams that experienced debris flows after their watersheds burned were remarkably different. They exhibited higher production and incident light and lower ecosystem respiration. Debris flows resulted in nearly complete removal of streamside vegetation, slowed recovery of the riparian canopy, and altered stream ecosystem metabolism. Our results suggest a synergistic interaction between wildfire and associated geomorphological processes whereby debris flows delay succession of stream ecosystems, possibly resulting in altered recovery trajectories, communities, and foodweb interactions

Present Effects of Past Wildfires on the Diets of Stream Fish

We investigated present indirect effects from a decade-old burn on the diets of stream fish. Based on soil instability and burn patterns from a 12–14-year-old wildfire complex, we separated 9 streams into 3 conditions: unburned, burned, and burned/scoured (i.e., experiencing a massive scour event 1 year post-burn). In the streams, we measured light levels and water temperatures, and we estimated fish density and biomass. We removed the digestive tracts from 9–15 rainbow trout (Oncorhynchus mykiss) from each stream and used a gravimetric procedure to analyze gut contents. Canopy cover development may dictate the composition of dietary items. Greater amounts of aquatic invertebrates and inorganic material were found in trout from streams with reduced overhead canopy. Further, these streams had lower amounts of terrestrial invertebrates and organic materials in the diets of fish. Although trout abundance was not different among the stream treatments, fire-induced, indirect effects on fish diets were still evident more than a decade after the burn. This suggests that recovery rates for trout assemblages may take longer than predicted and may depend on riparian recovery

DISSERTATION RESEARCH: Eco-Evolutionary Effects of an Aquatic Consumer: Linking Phenotypic Diversity to Community and Ecosystem Responses

This research addresses the interaction between ecological and evolutionary processes by examining the recent evolution of a common invasive fish species, the white perch, in lakes and the consequences of this evolution for community and ecosystem dynamics. White perch have successfully invaded lakes spanning a productivity gradient, which provides diverse selective pressures that may result in altered fish morphology, physiology and ecological role. Adaptation by these fish may, in turn, feed back to affect lake productivity and community structure through several ecological and chemical pathways. This project tests the hypothesis that this rapid evolutionary divergence within a single species has resulted in ecological effects that are large relative to longer term divergence between different species of fish. The research will use controlled rearing of fish from differing lakes to establish the genetic nature of the relationship between lake productivity and fish traits that include body chemistry, body shape, and feeding morphology. In additional, mesocosm experiments will be used to determine the effects of fish trait variation on plankton community structure and ecosystem processes such as nutrient cycling and productivity. By using mesocosms seeded with plankton and fish from different source ponds, fish and plankton source treatments will be crossed and the relative impact of fish invasion into novel habitats will be compared to longer term evolutionary divergence. This research tests an ecological-evolutionary framework that is a recent synthesis between evolutionary biology and ecology. This framework has the potential to provide general insight into the causes and consequences of biodiversity and a better understanding of the pace at which evolution and ecology interact. This theoretical framework and research that uses a common fish invader informs practical issues involving management and conservation of biodiversity and maintenance of water quality in lakes. This project will enhance the doctoral thesis of a graduate student and provide several undergraduate students with research experience

Present Effects of Past Wildfires on Leaf Litter Breakdown in Stream Ecosystems

We investigated the present effects from a 10-year-old wildfire on leaf litter breakdown rates in 3 headwater streams in central Idaho. These systems experienced a massive debris flow one year after the fire. Based on soil instability and burn patterns, we identified 3 stream conditions: unburned, burned only, and burned/scoured. We placed leaf bags containing willow leaves (Salix sp.) in each stream type and removed bags at various time intervals until all bags were collected 100 days after their introduction. Leaf material was dried and weighed, and decay rate coefficients were calculated. Macroinvertebrates colonizing the bags were enumerated and identified, and selected taxa were placed into trophic groups. We found that the unburned stream had the fastest leaf litter breakdown rate, the lowest level of incident light reaching the stream, and the largest amount of benthic organic matter. The burned/scoured stream was nearly opposite in all respects. Numbers of 2 detritivore invertebrate taxa, Serratella tibialis and Zapada oregonensis, were highest in the unburned stream but lowest in the burned/scoured stream. A third taxon, Baetis sp., showed the opposite relationship. Presence of predatory invertebrates did not affect detritivore abundance or leaf decay rate in the bags. Our research suggests that recovery response variables of some stream systems may not have returned to prefire levels even a decade after the initial wildfire. In this study, the recovery of our streams appears to be connected to the return of the riparian zone, though fire-induced debris flows may slow or alter final recovery of the stream system

The Effects of Wildfire and Debris Flows on Small Headwater Stream Ecosystems in Central Idaho

Disturbance is widely recognized as a fundamental structuring force in stream ecosystems and the biota that reside in them (Pringle et al. 1988, Resh et al. 1988). In western North America, wildfire is one of the primary natural disturbances influencing heterogeneity, patchiness, and diversity in both terrestrial landscapes and the streams that drain these landscapes (Resh et al. 1988, Swanson et al. 1994). Prior to the 1988 Greater Yellowstone Ecosystem fires, few studies had examined the impact of wildfire on stream ecosystems (Minshall et al. 1989). These large fires burned over 0.57 million ha, an area larger than 2 U.S. states (Minshall et al. 1989). Together, the growing interest in disturbance ecology and the high profile Yellowstone fires may have served as a catalyst, perhaps increasing the desire to understand the impacts of wildfire on stream habitats. This interest has only increased, culminating in whole journal issues devoted to their effects (Rieman et al. 2003)

Ecological Causes and Consequences of Trait Divergence in Invasive White Perch (Morone americana)

Evolutionary processes are now known to occur on contemporary, ecological time scales, leading both ecologists and evolutionary biologists to consider the importance of evolutionary dynamics to a variety of fields typically considered to be within the purview of ecology. However, the generality of interactions between ecology and evolution and the potential for dynamic feedbacks (i.e., eco-evolutionary dynamics) are poorly understood. In this research I addressed the hypothesis that trophic divergence in white perch (Morone americana) driven by a gradient of lake productivity would alter lake community structure and ecosystem function. The phenomenon of trophic divergence is commonly studied in sympatry; however, more modest trophic divergence may be common along environmental gradients in allopatry. Productivity is a dominant axis of ecological variation and was analyzed as a driver of perch trophic traits. Surveys across a productive state gradient of lakes revealed variation in a suite of perch traits, which suggested a benthic-eutrophic versus limnetic-oligotrophic dichotomy driven by relative resource availability in oligotrophic versus eutrophic lakes. Populations in eutrophic systems exhibited wider mouths and gill raker spacing, gibbose body shape, and longer fins compared to populations in oligotrophic systems. Trophic divergence was further associated with stroichiometric divergence, which can have ecological consequences in its own right. Modeling of stoichiometric divergence suggests it may explain between 5 and 24% of nitrogen and phosphorus excretion variation in fish populations. Considering predictions from trophic cascade and also ecological stoichiometry theory, I expected differential feeding in benthic versus limnetic habitats would lead to divergent ecological roles. Using mesocosm habitats stocked with fish from different source populations, I found that phenotype divergence in white perch altered several community and ecosystem parameters, including benthic invertebrates, nutrient concentrations and the production and limitation of primary producers. Importantly, these effects of fish phenotype varied with respect to background environmental conditions, suggesting that eco-evolutionary effects can be context dependent. In the perch system, context- dependent eco-evolutionary effects occur in a pattern which could reinforce the effects of cultural eutrophication in shifting lake systems to an alternate stable state

Climate match fails to explain variation in establishment success of non-native freshwater fishes in a warm climate region

For non-native species, climate can act as a primary filter limiting establishment. Numerous studies examining climate similarity between native and introduced regions have been completed for temperate areas, however we know little about how well climate matching performs for warmer regions. For non-native freshwater fish introduced to warm regions, one potential problem with climate matching is that fish from both temperate and tropical source regions could establish. Our goal was to examine whether climate matching can predict the establishment of non-native freshwater fish for a warm climate region. We used CLIMATCH, a widely applied climate matching program, to analyze climate similarity between source and target regions for 37 successfully established species and 36 species that have failed to establish. CLIMATCH was calculated in two ways for successfully established species, with Florida records included (post hoc) and without Florida records (a priori). The mean post hoc score for successful species was higher than that of failed species; however, the mean a priori score for successful species did not significantly differ from failed species. On average, post hoc scores were inflated 1.5 times over a priori scores. The post hoc result is tautological—the scores are high because the species is successful, and the species is successful because the scores are high. These results highlight two issues for climate matching: (1) as commonly done post hoc, degree of climate match and predictive power may be overestimated and (2) a priori applications may lack predictive power. We recommend consideration of these issues in the use and interpretation of CLIMATCH for prediction. Additional research into regional importance of climate variables (temperature and precipitation) is warranted, especially in warm climate regions

Thermal tolerance for three ornamental tankbuster catfishes

Pet abandonment is an important introduction vector for freshwater aquarium fishes, as unwanted pets become too large for tank dimensions and are released into the environment. Concerns over pet abandonment may be particularly important for the U.S. state of Florida, which exhibits abundant access to freshwater habitats and a climate more favorable to tropical aquarium fishes than other continental U.S. states. Numerous studies have examined the factors affecting establishment for non-native species, including the importance of propagule pressure and climate suitability. For freshwater aquarium species, maximum body size can increase pet abandonment because they grow too large for the tank dimensions (i.e., “tankbusters”). Thus, large maximum body size may increase propagule pressure due to intentional release. In addition to being introduced in sufficient numbers, a match between the thermal tolerance of a species and the thermal habitat is necessary for establishment. Several large-bodied catfishes are found in the aquarium trade, including the goonch Bagarius spp., redtail catfish Phractocephalus hemioliopterus, and tiger sorubim Pseudoplatystoma tigrinum. Here, we experimentally determined the chronic lethal minimum temperature (CLmin) for the three catfishes. CLMin estimates for these three species were higher than many other ornamental species, highest for the redtail catfish (14.3 °C), lower for the tiger sorubim (11.0 °C), and lowest (9.9 °C) for the goonch. Given these lethal temperatures, the distribution of redtail catfish would be limited to South Florida while the tiger sorubim and goonch could live, provided other habitat characteristics are suitable, up to ~28°N Latitude in Florida

Characterizing the US trade in lionfishes.

Invasive lionfishes Pterois volitans and Pterois miles have spread throughout the tropical western Atlantic Ocean, Gulf of Mexico, and Greater Caribbean. Beyond these two invaders, additional species within the subfamily Pteroinae are regularly imported into the United States. We evaluated the trade of lionfishes as a surrogate measure for propagule pressure, an important component of invasion success. Proactive evaluation of marine ornamental fishes in trade is vital, particularly for those sharing characteristics with known invaders. We utilized one year of import records from the U.S. Fish and Wildlife Service's Law Enforcement Management Information System database and two domestic databases to capture the trade of all lionfishes in the US, the invasive complex in its invaded range in Florida, and two Hawaiian endemic lionfishes. Retail surveys were completed to assess lionfish availability across 10 coastal states. Compared to species diversity within the subfamily, the number of traded species was low and just two species were traded at moderate to high volume, including P. volitans and Dendrochirus zebra. At the retail level, fewer species are available to consumers. The trade in lionfishes is consolidated because most lionfishes originate from two Indo-Pacific countries and arrive through the port of Los Angeles. The volume and diversity of traded lionfishes presents some risk of introduction for lionfishes which are not established, and secondary introductions of the invasive P. volitans. In combination with rapid risk screening, this research can be applied to a proactive risk management framework to identify risky species prior to introduction and establishment