Susan Kilham - Academia.edu (original) (raw)

Papers by Susan Kilham

Anthropogenic inputs of nitrogen from human sewage are a central concern in urban watershed manag... more Anthropogenic inputs of nitrogen from human sewage are a central concern in urban watershed management. However, identifying the locations of these inputs, whether from improperly functioning or ill-maintained septic tanks or from leaking sewer lines, is difficult. We used nitrogen stable isotope analysis of aquatic food webs as indicators of sewage-derived nitrogen in Valley Creek watershed. Stable nitrogen isotope analysis revealed elevated δ N in all trophic levels at stations located downstream of the divide between sewered and non-sewered (septic tanks) neighborhoods in the watershed. Stations not located in the septic system area or on the other branch of the creek did not show this elevated level of δ N. Allochthonus inputs, that do not derive nitrogen from aquatic sources, such as detrital leaf material, showed no difference in δ N between Valley Creek and Little Valley Creek. Particular fish species that are found throughout both branches, such as blacknose dace and creek c...

SIL Proceedings, 1922-2010

Scientific reports, Jan 18, 2017

Population variation in trophic niche is widespread among organisms and is of increasing interest... more Population variation in trophic niche is widespread among organisms and is of increasing interest given its role in both speciation and adaptation to changing environments. Trinidadian guppies (Poecilia reticulata) inhabiting stream reaches with different predation regimes have rapidly evolved divergent life history traits. Here, we investigated the effects of both predation and resource availability on guppy trophic niches by evaluating their gut contents, resource standing stocks, and δ(15)N and δ(13)C stable isotopes across five streams during the wet season. We found that guppies from low predation (LP) sites had a consistently higher trophic position and proportion of invertebrates in their guts and assimilate less epilithon than guppies from high predation (HP) sites. Higher trophic position was also associated with lower benthic invertebrate availability. Our results suggest that LP guppies could be more efficient invertebrate consumers, possibly as an evolutionary response t...

Ecological Applications, 2016

Emerging infectious diseases can cause host community disassembly, but the mechanisms driving the... more Emerging infectious diseases can cause host community disassembly, but the mechanisms driving the order of species declines and extirpations following a disease outbreak are unclear. We documented the community disassembly of a Neotropical tadpole community during a chytridiomycosis outbreak, triggered by the generalist fungal pathogen, Batrachochytrium dendrobatidis (Bd). Within the first 11 months of Bd arrival, tadpole density and occupancy rapidly declined. Species rarity, in terms of tadpole occupancy and adult relative abundance, did not predict the odds of tadpole occupancy declines. But species losses were taxonomically selective, with glassfrogs (Family: Centrolenidae) disappearing the fastest and tree frogs (Family: Hylidae) and dart-poison frogs (Family: Dendrobatidae) remaining the longest. We detected biotic homogenization of tadpole communities, with post-decline communities resembling one another more strongly than pre-decline communities. The entire tadpole community was extirpated within 22 months following Bd arrival, and we found limited signs of recovery within 10 years post-outbreak. Because of imperfect species detection inherent to sampling species-rich tropical communities and the difficulty of devising a single study design protocol to sample physically complex tropical habitats, we used simulations to provide recommendations for future surveys to adequately sample diverse Neotropical communities. Our unique data set on tadpole community composition before and after Bd arrival is a valuable baseline for assessing amphibian recovery. Our results are of direct relevance to conservation managers and community ecologists interested in understanding the timing, magnitude, and consequences of disease outbreaks as emerging infectious diseases spread globally.

ABSTRACT As part of a comprehensive investigation of the effects of urbanization on Valley Creek ... more ABSTRACT As part of a comprehensive investigation of the effects of urbanization on Valley Creek watershed near Philadelphia, Pennsylvania, we are attempting to utilize documented historical and ongoing changes to the watershed to elucidate process-based watershed dynamics, particularly as related to the connections between the surface and groundwater systems. Valley Creek is underlain principally by fractured limestone and dolomite. The watershed is extensively developed, as quantified by 17% impervious area. This percentage is expected to increase due to ongoing and planned development projects. A variety of methods are being utilized to characterize the hydrologic and nutrient dynamics of the watershed. For example, a limestone quarry located upstream of the geographic and hydrologic center of the watershed has historically discharged accumulated groundwater seepage into the stream on an approximately 3 -1/2 hour cyclical basis. At the peak pumping rate, the quarry flow has constituted 20% to 50% of the surface water discharge of the entire watershed, as measured at a USGS gauging station located near the mouth of the main stem of Valley Creek. At the same time, a hazardous waste site on the property of an abandoned mineral processing plant located in the headwaters of the main stem of Valley Creek has resulted in a significant steady concentration of bromide entering the stream through faults and fractures of the limestone formation. This has resulted in bromide-free groundwater from the quarry entering the main stem of bromide-laden Valley Creek on a cyclical basis, thus allowing bromide from the mineral plant to be used as a tracer to assess the stream response to the quarry inflow. We measured the fluctuating bromide concentration at three stations over a 24-hour period. The decreasing amplitude and phase shift of the bromide sinusoidal wave as it moved 7 km downstream was evident. We have calibrated a transient hydrodynamic and transport model to the resulting data set to interpret the longitudinal dispersion and hyporheic storage parameters of Valley Creek. This work illustrates how anthropogenic perturbations can be used to advantage to interpret process-based physical characteristics of an urbanizing watershed. Additional conservative and reactive tracer injection experiments, sediment nutrient uptake experiments and measurements of community metabolism are being conducted on smaller reaches immediately downstream of active development projects. Data from this ongoing monitoring will be used to determine the impact of development on the hyporheic characteristics and nutrient dynamics of Valley Creek.

Can J Fisheries Aquat Sci, 1984

Growth rates for five freshwater algae, Asterionella formosa, Stephanodiscus hantzschii, Scenedes... more Growth rates for five freshwater algae, Asterionella formosa, Stephanodiscus hantzschii, Scenedesmus sp., Cryptomonas ozolini, and Anabaena flos-aquae, in media ranging in pH from 5.0 to 7.5 using three zwitterionic buffers, MES, PIPES, and TES, were determined. These buffers supported similar growth rates when compared with each other in treatment groups of similar pH. For pH values below 6.0 no growth occurred or growth rates were significantly reduced in some treatment groups for all species except Cryptomonas. In some cases, these lowered growth rates were partially or completely restored by reducing trace metals in the media by one or two orders of magnitude. We suggest that these buffers could provide a useful technique for investigating the physiological responses of phytoplankton in lakes undergoing acidification.

Bull Environ Contam Toxicol, 1983

Brock/Springer Series in Contemporary Bioscience, 1990

Freshwater Biology, 2013

ABSTRACT Despite the typically high taxonomic and functional diversity of tropical habitats, litt... more ABSTRACT Despite the typically high taxonomic and functional diversity of tropical habitats, little is known about the roles of individual consumers in their ecosystem structure and function. We studied the trophic basis of production in a tropical headwater stream by identifying major sources of energy, measuring energy flow through consumers and characterising interactions among trophic levels and functional groups.We examined gut contents of 18 dominant macroinvertebrate and two tadpole taxa and used these data, along with previously published estimates of secondary production, to quantify food-web structure and energy flow pathways. We also examined the prevalence of omnivory and patterns of resource consumption across seasons and habitats.Non-algal biofilm, a heterogeneous polysaccharidic matrix, was the most utilised food resource in the stream. Contrary to some studies of Old World tropical stream food webs, detrital energy sources were consumed at relatively high rates and contributed significantly to overall energy flow, although much of this was attributable to a single shredder taxon. Algal consumption rates were similar to values reported for temperate streams and were highest during the dry season.Omnivory was prevalent across all functional groups, particularly predators, suggesting traditional functional and trophic assignments based on temperate regions may not be appropriate for tropical systems. Seasonal patterns of resource consumption appeared linked to hydrological disturbance.This is the first study to provide quantitative estimates of energy flow through a neotropical stream food web. Extirpation and extinction rates in tropical freshwater habitats are high; our study provides baseline information for conservation and management of remaining systems, and for quantifying the consequences of further losses of biodiversity such as ongoing amphibian declines.

Bulletin of Environmental Contamination and Toxicology, 1983

PLOS ONE, 2015

Phenotypic plasticity is advantageous for organisms that live in variable environments. The diges... more Phenotypic plasticity is advantageous for organisms that live in variable environments. The digestive system is particularly plastic, responding to changes in diet. Gut length is the result of a trade-off between maximum nutrient absorption and minimum cost for its maintenance and it can be influenced by diet and by evolutionary history. We assessed variation in gut length of Trinidadian guppies (Poecilia reticulata) as a function of diet, season, ontogeny, and local adaptation. Populations of guppies adapted to different predation levels have evolved different life history traits and have different diets. We sampled guppies from sites with low (LP) and high predation (HP) pressure in the Aripo and Guanapo Rivers in Trinidad. We collected fish during both the dry and wet season and assessed their diet and gut length. During the dry season, guppies from HP sites fed mostly on invertebrates, while guppies in the LP sites fed mainly on detritus. During the wet season, the diet of LP and HP populations became very similar. We did not find strong evidence of an ontogenetic diet shift. Gut length was negatively correlated with the proportion of invertebrates in diet across fish from all sites, supporting the hypothesis that guppy digestive systems adapt in length to changes in diet. Population of origin also had an effect on gut length, as HP and LP fish maintained different gut lengths even in the wet season, when their diets were very similar and individuals in both types of populations fed mostly on detritus. Thus, both environment and population of origin influenced guppies gut length, but population of origin seemed to have a stronger effect. Our study also showed that, even in omnivorous fish, gut length adapted to different diets, being more evident when the magnitude of difference between animal and plant material in the diet was very large.

Background/Question/Methods As species are extirpated, ecosystem productivity will likely decline... more Background/Question/Methods As species are extirpated, ecosystem productivity will likely decline with concomitant declines in food web structure as linkages are removed. Catastrophic amphibian extirpations in Central America can affect ecosystem function, but have unknown consequences on food web structure. We empirically assessed periphyton-insect food webs, both before and after (5 yrs) a disease-driven amphibian extirpation in a highland Panamanian stream. Food webs were constructed using gut content analysis of 891 tadpoles and insects to identify 1793 linkages from four food webs: pools and riffles with and without tadpoles. For each food web, fourteen structural properties were estimated and the effect size was measured between pre- and post-decline food webs. Simulations using pre-decline food webs that reflected the loss of tadpoles and cascading extirpations of macroinvertebrates, were then compared with the observed post-extirpation food web to quantify the robustness of ...

Freshwater Biology

1. Information about temporal patterns of ecological responses to species losses is integral to o... more 1. Information about temporal patterns of ecological responses to species losses is integral to our understanding of the ultimate effects of declining biodiversity. As part of the Tropical Amphibian Declines in Streams (TADS) project, we quantified changes in algal biomass and N cycling in algae in upland Panamanian streams following the widespread decline of larval anurans. 2. Reach-scale monitoring during and after a catastrophic, disease-driven amphibian decline showed significant 2.8-fold increases (P < 0.05) in algal biomass in pools and 6.3-fold increases in riffles in the 5 months following the decline. 3 years after the decline, the magnitude of this initial change dampened to increases (P < 0.05) of 2-fold in pools and 3.5-fold in riffles over pre-decline levels. Similarly, total organic matter of benthic biofilms, measured as ash-free dry mass (AFDM), increased significantly by 2.2-fold in pools and 2.3-fold in riffles in the initial 5-month post-decline period, with...