Browsing by Author "Kemp, Stanley J."
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Item An approach for determining relative input parameter importance and significance in artificial neural networks(Elsevier, 2007) Kemp, Stanley J.; Zaradic, Patricia A.; Hansen, FrankArtificial neural network (ANN) models are powerful statistical tools which are increasingly used in modeling complex ecological systems. For interpretation of ANN models, a means of evaluating how systemic parameters contribute to model output is essential. Developing a robust, systematic method for interpreting ANN models is the subject of much current research. We propose a method using sequential randomization of input parameters to determine the relative proportion to which each input variable contributes to the predictive ability of the ANN model (termed the holdback input randomization method or HIPR method). Validity of the method was assessed using a simulated data set in which the relationship between input parameters and output parameters were completely known. Simulated data sets were generated with known linear, nonlinear, and collinear relationships. The HIPR method was performed repetitively on ANN models trained on these data sets. The method was successful in predicting rank order of importance on all data sets, performing as well as or better than the recently proposed connectivity weight method. One main advantage of using this method relative to others is that results can be obtained without making assumptions regarding the architecture of the ANN model used. These results also serve to illustrate the consistency and information content of ANN models in general, and highlight their potential use in exploring ecological relationships. The HIPR method is a robust, simple, general procedure for interpreting complex ecological systems as captured by ANN models.Item Autecological effects of habitat alteration: Trophic changes in mangrove marsh fish as a consequence of marsh impoundment(Elsevier, 2008) Kemp, Stanley J.The key to predicting, counteracting, and managing environmental change is understanding the mechanisms through which habitat change affects populations of organisms. The mangrove ecosystem of the Indian River Lagoon (IRL), east-central Florida, has been impounded for the purpose of mosquito control and is representative of such large-scale alterations. Sailfin mollies Poecilia latipinna in this system exhibit significant interpopulation differences in adult body size in relation to habitat alteration. One likely hypothesis for this pattern is the apparent change in diet experienced as a result of impounment, as has been documented in earlier studies. To address the question of whether these dietary changes would have been sufficient to cause trophic differences in P. latipinna populations relative to impoundment, a comparative study of trophic position in 2 size-divergent populations of P. latipinna using stable isotopes was employed. Results suggested that P, latipinna from an unimpounded site had a slightly higher trophic position than those from an impounded site and may constitute a partial explanation of differences in adult body size between the 2 populations. Results from the present study also showed that there was a fundamental difference in energy source between the study sites, which suggests greater assimilation of mangrove-based carbon in impoundments. Specific population- and community-level effects of impoundment on mangrove habitats have been demonstrated, indicating a mechanistic link between anthropogenic habitat alteration and life history of P. latipinna.Item Autecological effects of habitat alteration: trophic changes in mangrove marsh fish as a consequence of marsh impoundment(Marine Ecology Progress Series, 2008-11-19) Kemp, Stanley J.The key to predicting, counteracting, and managing environmental change is understanding the mechanisms through which habitat change affects populations of organisms. The mangrove ecosystem of the Indian River Lagoon (IRL), east-central Florida, has been impounded for the purpose of mosquito control and is representative of such large-scale alterations. Sailfin mollies Poecilia latipinna in this system exhibit significant interpopulation differences in adult body size in relation to habitat alteration. One likely hypothesis for this pattern is the apparent change in diet experienced as a result of impoundment, as has been documented in earlier studies. To address the question of whether these dietary changes would have been sufficient to cause trophic differences in P. latipinna populations relative to impoundment, a comparative study of trophic position in 2 size divergent populations of P. latipinna using stable isotopes was employed. Results suggested that P. latipinna from an unimpounded site had a slightly higher trophic position than those from an impounded site and may constitute a partial explanation of differences in adult body size between the 2 populations. Results from the present study also showed that there was a fundamental difference in energy source between the study sites, which suggests greater assimilation of mangrove based carbon in impoundments. Specific population- and community-level effects of impoundment on mangrove habitats have been demonstrated, indicating a mechanistic link between anthropogenic habitat alteration and life history of P. latipinna.Item Behavioral Responses to Barriers by Desert Tortoises: Implications for Wildlife Management(Allen Press, 1994) Ruby, Douglas E.; Spotila, James R.; Martin, Stacia K.; Kemp, Stanley J.We conducted tests on the behavioral responses of captive desert tortoises (Gopherus agassizii) to barriers and highway obstacles. Desert tortoises are slow-moving but persistent wanderers in their natural habitat. Consequently, they move substantial distances when they meet a barrier that they cannot go around. Tortoises responded differently to solid and non-solid barriers when placed in small pens constructed of various materials. Our tests indicated that a screen mesh with small enough openings to exclude a tortoise's head was the most suitable barrier material. When tortoises were tested for 2 h periods or after an overnight stay in a barrier pen, rates of responses with barriers declined with time but tortoises continued movement along the barrier. In a choice situation, we found no preference by tortoises for following either solid or mesh barrier fences. Tortoises quickly walked past openings in a barrier which were too small to enter but easily escaped from a barrier pen within 30 min when openings of an appropriate size were available. We found tortoises willingly entered culverts under large highways and retreated from concrete highways barriers.Item Ecology of life history variation in the sailfin molly (Poecilia latipinna) in impounded mangrove marsh of the Indian River Lagoon, Florida(2004) Kemp, Stanley J.Effects of environmental change can be very complex and multifaceted, and as a result, the greatest challenge facing ecologists today is the prediction of the effects of these changes on populations of organisms. This dissertation is a study of the effects of an ecosystem-wide alteration of habitat on the life history of populations of a resident organism. Sailfin molly ( Poecilia latipinna ) populations residing in mangrove habitats affected by impoundment provide an ideal opportunity to study ecological aspects of environmental change. Much previous research on the life history of sailfin mollies and mosquito impoundments has been done independently, and the goal of this study was to couple this information with system- specific study to outline the chain of causation of life history patterns in the sailfin molly observed in this system. Following a system-wide survey to identify life history patterns of the sailfin molly in relation to impoundment (Chapter 2), it was found that significant variation existed related to impoundment for two traits: adult body size and somatic lipid content. Research centered on three likely effects impoundment may have had on the growth, survival, and reproduction of sailfin mollies in the impounded mangrove habitat to produce these life history patterns: (1) changes in physical conditions (Chapters 3-4), (2) fish species assemblages (Chapter 5), and (3) through changes in diet (Chapter 6). Impoundment was significantly related to all three of the factors studied. However, the relationship between the variation in the factors studied and life history patterns was not immediately apparent. While much research has been done on sailfin mollies and mosquito impoundments independently, results of this study suggest an entirely different pattern of causation than that observed in other studies. Taken together, they suggest an entirely new series of hypotheses centered on the interaction between specific effects of impoundment. The results of this study support the hypothesis that the factors linking impoundment to life history patterns in the sailfin molly are multiple and possibly interacting, and also raise questions regarding the generality of ecological studies outside of the particular system in question.Item Effects of Incubation Conditions on Sex Determination, Hatching Success, and Growth of Hatchling Desert Tortoises, Gopherus agassizii(1994) Spotila, James R.; Zimmerman, L. C.; Binckley, Christopher; Grumbles, Janice; Rostal, David C.; List, A. Jr.; Beyer, E. C.; Phillips, K. M.; Kemp, Stanley J.Incubation temperature has a direct effect on sex determination of the desert tortoise. Low temperatures (26.0-30.6 C) produce males and high temperatures (32.8-35.3 C) produce females. Pivotal temperature is approximately 31.8 C. Macroscopic and microscopic anatomy of the gonads is similar to that of other turtles. Hatching success and survival is very good between 28.1 and 32.8 C in dry sand (-5000 kPa). Incubation at 35.3 C is lethal for 72% of the eggs and produces weak hatchlings that die within 45 days. Wet sand (-5 kPa) is lethal for desert tortoise eggs. Hatchling size was dependent upon egg size and incubation condition. Hatchlings from eggs incubated at 32.8 and 35.3 C were significantly smaller than hatchlings from eggs incubated at 28.1 and 30.6 C. Hatching mass had no effect on growth rate of hatchlings. Thus, large eggs produced large hatchlings that were larger than their siblings at 120 days of age. Hatchlings from eggs incubated at 30.6 C grew significantly more than hatchlings incubated at 28.1 and 32.8 C. Hatchlings incubated at 35.3 C lost mass. Incubation condition did not affect temperature selected in a substrate thermal gradient when hatchlings were tested within one week (x = 29.2 C) or 40 days of hatching (x = 26.6 C). Because of temperature-dependent sex determination and the effect of incubation conditions on hatching success and later growth, management strategies for the desert tortoise should be very conservative. To ensure normal sex ratios of desert tortoises, natural vegetation communities and native soil composition and structure must be preserved or restored. Long term recovery and survival of desert tortoises can only be assured when we have information on pivotal temperatures and nesting ecology for its various populations.Item Effects of Urbanization on Brown Trout Salmo Trutta, Other Fishes and Macroinvertebrates in Valley Creek, Valley Forge, Pennsylvania(American Midland Naturalist, 1997) Kemp, Stanley J.; Spotila, James R.We determined the effects of urbanization on fish and benthic macroinvertebrate communities of Valley Creek and its tributary, Little Valley Creek, in southeastern Pennsylvania. Brown trout (Salmo trutta) were a major component of the fish community except in the urbanized upstream portions of the watershed. Growth rates and condition factors of brown trout were within the upper range of reported values, indicating high productivity in the nonurbanized portions of the Valley Creek system. In the urbanized portion of the watershed, fish communities and benthic macroinvertebrate communities consisted of pollution-tolerant species (e.g., Semotilus atromaculatus, Lepomis cyanellus, Isopoda) and brown trout were absent. In nonurbanized areas, pollution-tolerant fish and benthos declined while less tolerant species (Salmo trutta, longnose dace; Rhinichthys cataractae, darters; Etheostoma olmstedi, cutlip shiners; Exoglossum maxillingua, and invertebrates such as Amphipoda, Ephemeroptera, and Trichoptera) increased. Regressions of community-level patterns (species richness, diversity, evenness, number of trout, number of age-0) trout) vs. watershed physical characteristics (stream order, distance from source, stream discharge, water temperature) differed between the two main branches of the stream (Valley Creek, Little Valley Creek). This indicated that localized factors related to urbanization differentially affected these areas. Dramatic changes in the fish and benthic communities in the most urbanized sections of Valley Creek demonstrated the deleterious impacts associated with increasing urbanization of file watershed.Item Effects of urbanization on fish communities in Valley Creek, Valley Forge, PA(1994) Kemp, Stanley J.Item Phylogeny, Regression, and the Allometry of Physiological Traits(Essex Institute, 2007) O'Connor, Michael P.; Agosta, Salvatore J.; Hansen, Frank; Kemp, Stanley J.; Sieg, Annette E.; McNair, James N.; Dunham, Arthur E.Physiological and ecological allometries often pose linear regression problems characterized by (1) noncausal, phylogenetically autocorrelated independent (x) and dependent (y) variables (characters); (2) random variation in both variables; and (3) a focus on regression slopes (allometric exponents). Remedies for the phylogenetic autocorrelation of species values (phylogenetically independent contrasts) and variance structure of the data (reduced major axis [RMA] regression) have been developed, but most functional allometries are reported as ordinary least squares (OLS) regression without use of phylogenetically independent contrasts. We simulated Brownian diffusive evolution of functionally related characters and examined the importance of regression methodologies and phylogenetic contrasts in estimating regression slopes for phylogenetically constrained data. Simulations showed that both OLS and RMA regressions exhibit serious bias in estimated regression slopes under different circumstances but that a modified orthogonal (least squares variance-oriented residual [LSVOR]) regression was less biased than either OLS or RMA regressions. For strongly phylogenetically structured data, failure to use phylogenetic contrasts as regression data resulted in overestimation of the strength of the regression relationship and a significant increase in the variance of the slope estimate. Censoring of data sets by simulated extinction of taxa did not affect the importance of appropriate regression models or the use of phylogenetic contrasts.Item The potential and limitations of linking biological monitoring data and restoration needs of urbanized waterways: a case study(Springer, 2014) Kemp, Stanley J.The implementation of effective strategies to mitigate the impacts of urbanization on waterways represents a major global challenge. Monitoring data plays an important role in the formulation of these strategies. Using monitoring and historical data compiled from around an urban area (Baltimore, USA), this paper is an assessment of the potential and limitations of the use of fish assemblage monitoring data in watershed restoration. A discriminant analysis between assemblages from urban and reference sites was used to determine faunal components which have been reduced or eliminated from Baltimore area waterways. This analysis produced a strong discrimination between fish assemblages from urban and reference sites. Species primarily associated with reference sites varied taxonomically and ecologically, were generally classified as pollution intolerant, and were native. Species associated with urbanized sites were also native, varied taxonomically and ecologically, and were mixed in pollution tolerance. One factor linking most species associated with reference sites was spawning mode (lithophilic). Spawning habitat limitations may be the mechanism through which these species have been reduced in the urbanized faunas. While this presents a strong general hypothesis, information regarding the specific habitat requirements and responses to urbanization of these species is limited. This represents a limitation to producing effective restoration strategies based on exact goals and targets. Without these, determining the type and number of restoration activities required to restore ecological communities remains problematic.Item The potential and limitations of linking biological monitoring data and restoration needs of urbanized waterways: a case study(Environmental Monitoring and Assessment, 2014) Kemp, Stanley J.;The implementation of effective strategies to mitigate the impacts of urbanization on waterways represents a major global challenge. Monitoring data plays an important role in the formulation of these strategies. Using monitoring and historical data compiled from around an urban area (Baltimore, USA), this paper is an assessment of the potential and limitations of the use of fish assemblage monitoring data in watershed restoration. A discriminant analysis between assemblages from urban and reference sites was used to determine components which have been reduced or eliminated from Baltimore area waterways. This analysis produced a strong discrimination between fish assemblages from urban and reference sites. Species primarily associated with reference sites varied taxonomically and ecologically, were generally classified as pollution intolerant, and were native. Species associated with urbanized sites were also native, varied taxonomically and ecologically, and were mixed in pollution tolerance. One factor linking most species associated with reference sites was spawning mode (lithophilic). Spawning habitat limitations may be the mechanism through which these species have been reduced in the urbanized faunas. While this presents a strong general hypothesis, information regarding the specific habitat requirements and responses to urbanization of these species is limited. This represents a major limitation to producing effective restoration strategies based on exact goals and targets. Without these, determining the type and number of restoration activities required to restore ecological communities remains problematicItem Predicting Ecological Effects of Watershed-Wide Rain Garden Implementation Using a Low-Cost Methodology(American Society of Civil Engineers, 2015) Dovel, Erin L.; Kemp, Stanley J.; Welker, AndreaStormwater control measures (SCMs) have been employed to mitigate peak flows and pollutants associated with watershed urbanization. Downstream ecological effects caused by the implementation of SCMs are largely unknown, especially at the watershed scale. Knowledge of these effects could help with setting goals for and targeting locations of local restoration efforts. Unfortunately, studies such as these typically require a high level of time and effort for the investigating party, of which resources are often limited. This study proposes a low-cost investigation method for the prediction of ecological effects on the watershed scale with the implementation of rain garden systems by using publicly available data and software. For demonstration purposes, a typical urban watershed was modeled using Storm Water Management Model (SWMM) 5.0. Forty-five models were developed in which the percent impervious area was varied 3 to 80%, and the fraction of rain gardens implemented with respect to the number of structures was varied from 0 to 100%. The river chub fish (Nocomis micropogon) and its congeners (Nocomis spp.) were chosen as ecological indicators, as they are considered to be keystone species through interspecific nesting association. Depth and velocity criteria for successful nest building locations of the river chub were determined; these criteria can then be applied to many other watersheds. In this study, both base flow conditions and a typical summer storm event (1.3cm, 6h duration) were evaluated. During the simulated storm, nest-building locations were not affected in the 3 and 5% impervious cover models. Nest destruction was found to occur in approximately 54% of the original nest building sites for the 9% and 10% impervious areas. Nearly all of the nest-building locations were uninhabitable for impervious areas 20% and greater. Rain garden implementation significantly improved river chub habitat in the simulation, with greatest marginal benefit at lower levels of implementation.Item Predicting impacts of urbanized stream processes on biota: high flows and river chub (Nocomis micropogon) nesting activity(Springer, 2017) Kemp, Stanley J.This study quantified the impact of high stream flows on reproductive activities of river chub (Nocomis micropogon). Using observed relationships between flow and reproductive activities, the number of predicted damaging flow events was compared between streams with extant river chub populations and urbanized streams. Monitoring the survivorship of river chub nests during 2013–2014 (N = 101) revealed consistent relationships between interval peak flow measured at flow gauges and the integrity of river chub nests within sites. Flow-mediated disruption of nests was frequent, and interval peak flows were significantly correlated with nest erosion rates. Logistic regression between fate of river chub nests and standardized peak flow (Qs) during monitoring intervals identified thresholds of peak flow corresponding to complete and partial destruction of river chub nests. Observed thresholds were used to predict the frequency of potentially damaging flows in urbanized versus river chub study streams, based on archival flow monitoring data. Repeated measures analysis revealed that the frequency of flows predicted to result in the loss of all nests was significantly higher in urbanized streams (F = 122.2; df = 1; P < 0.001 ). While key life history information needs to be determined to fully understand the impacts of high flows on river chub population dynamics, results indicate the disruption of nests through frequent high flows as a mechanism for the reduction of this important species in urbanized areas. Improved understanding of the interactions between stream processes and biota will aid in the design of specific stream protection and restoration strategies.Item Reconsidering the mechanistic basis of metabolic theory of ecology(2007) O'Connor, Michael P.; Kemp, Stanley J.; Agosta, Salvatore J.; Hansen, Frank; Sieg, Annette E.; Wallace, Bryan P.; McNair, James N.; Dunham, Arthur E.The recently proposed metabolic theory of ecology (MTE) claims to provide a mechanistic explanation for long known allometric relationships between mass and metabolic rate. The MTE postulates that these patterns of allometry are driven by the primary selective constraint of transport of energy and materials. However, recent evidence along several different lines has called into question both the adequacy and the universality of this mechanism. We review the accumulating body of literature on this subject, adding our own concerns and criticisms. In addition to other difficulties, we argue that MTE fails as a mechanistic explanation of mass versus metabolic rate allometries because: 1) circulatory cost minimization is not a tenable criterion for evolutionary optimization, 2) the Boltzmann type relationships on which MTE depends are inadequate descriptors of complex metabolic pathways, and 3) most of the hypotheses advanced by the MTE do not, in fact, depend on the proposed mechanism and therefore cannot be used to test the theory. We conclude that the MTE should be abandoned as a monolithic explanation for allometric patterns, and that a more realistic path toward a better understanding of allometry would be to consider multiple explanatory mechanisms for physiological allometries.Item Thermal Ecology of Desert Tortoises in the Eastern Mojave Desert: Seasonal Patterns of Operative and Body Temperatures, and Microhabitat Utilization(Allen Press, 1994) Zimmerman, Linda C.; O'Connor, Michael P.; Bulova, Susan J.; Spotila, James R.; Kemp, Stanley J.; Salice, Christopher J.We monitored meteorological variables, daily and seasonal patterns of body temperature, corresponding operative temperatures, and microhabitat utilization by desert tortoises (Gopherus agassizii) during the 1991 and 1992 activity seasons of tortoises in the eastern Mojave desert. We studied tortoises in enclosures of natural habitat at the Desert Tortoise Conservation Center (DTCC) near Las Vegas, Nevada and a population of free-ranging tortoises in a field site adjacent to the DTCC. Air, ground and operative temperatures coincided with daily and monthly patterns of incident solar radiation. Variation in body temperature was primarily a consequence of microhabitat selection, principally use of burrows. During July-October, in the morning, body temperatures of tortoises in burrows were cooler than those of individuals on the surface. During midday, tortoises remained in burrows where body temperatures were cooler than extreme surface operative temperatures. While tortoises remained in burrows during much of the day, tortoises typically did not sleep in burrows at night. Microhabitat utilization was dictated by avoidance of extreme temperatures during midday, and microhabitat selection corresponded qualitatively to maintenance of energy and water balances. Effective conservation efforts to preserve habitat of desert tortoises will focus upon managing variables associated with integrity of burrows.