Howard H. Whiteman
GENERAL RESEARCH INTERESTS AND PHILOSOPHY
Rocky Mountain Biological Laboratory: Amphibians
General Research Interests and Philosophy
My research is currently centered in conservation biology and evolutionary ecology. The majority of my work focuses on conservation-oriented projects, such as the mechanisms and ecological consequences of population fluctuations; the role of trophic cascades in maintaining and restoring biodiversity; the effects of anthropogenic toxicants on development, life history, and population growth; the impact of invasive species management on native fauna; and the ecology of reintroduction efforts. My goal is to conduct fundamental science that will lead to positive management efforts and improvements in biodiversity conservation.
I began my research career focused on evolutionary ecology, and I continue to explore questions centered on polyphenisms (environmentally induced polymorphisms). Polyphenisms provide useful models for understanding phenotypic plasticity, reproductive isolation, speciation, and the production and maintenance of biodiversity. It is a goal of my research to improve our understanding of the evolutionary mechanisms maintaining polyphenisms, and to relate our understanding of polyphenisms to the evolution of phenotypic plasticity, speciation, and biodiversity.
I have used a variety of approaches during my research, including the development of theory, natural observations, laboratory and field experiments, and modeling. I believe that collaboration is an extremely beneficial and enjoyable way to conduct research, and thus I often work with teams of faculty and students focused on solving specific research problems. Additionally, I have committed my career to the training of graduate and undergraduate students, and have found the interactions with them to be synergistic in terms our mutual growth as scientists and the success of our collaborative research.
Biodiversity loss has been increasing at an alarming rate, with human population growth and habitat destruction the most widely cited causes. Such losses have been particularly evident among amphibian populations, which have disappeared or declined throughout the world. Amphibians are important indicators of ecosystem health, because they often spend part of their life cycle in water, and part on land, and thus are exposed to contaminants and habitat loss in both environments. Because of their important role as ecological indicators, much of my research focuses on amphibian conservation.
Mechanisms of Population Fluctuation
Amphibian populations have been well documented to fluctuate dramatically, in part because of the high fecundity of females and the dynamic nature of their breeding habitats (e.g., drought, competition, predation). Although several studies have documented fluctuations in amphibian populations, no research has examined the ecological mechanisms of such fluctuation in detail. This is a major cause of concern: how can one determine a true decline from population fluctuation, particularly in a species that fluctuates so much?
In 1990 Scott Wissinger (Allegheny College) and I began to follow a high-elevation metapopulation of tiger salamanders, Ambystoma tigrinum nebulosum, at the Mexican Cut Nature Preserve. Over the past two decades, our research has elucidated much about the life-history strategies of the salamanders (see below), and the effects of the salamander predators on invertebrate prey (Bohonak and Whiteman 1999, Wissinger et al. 1999a, b). It has also allowed us to begin to recognize the mechanisms that produce the fluctuations evident in this population (Fig. 1). We have identified a number of extrinsic and intrinsic variables likely to be important to these population fluctuations, including drought, winter mortality, cannibalism, and demographic convergence among adults (Whiteman and Wissinger 2005). Most recently, we used both observational and experimental approaches to show that cannibalism by large larvae and aquatic adults called paedomorphs (see below) was critical in reducing recruitment of larval cohorts, and thus may be primarily responsible for the decline phases of the population fluctuations (Wissinger et al. 2010). Current research is focusing on understanding the life-history mechanisms producing "boom" cohorts, and the community and ecosystem consequences of population fluctuations in a top predator. Because Mexican Cut is only minimally affected by anthropogenic impacts, our data serve as an excellent baseline for understanding amphibian population fluctuations.
Conservation Planning and Trophic Cascades Research for the Kimball Creek Watershed Restoration
Fig. 3: View of the Kimball Creek valley, showing emergence traps deployed in the stream to quantify invertebrate emergence rates.
The newest project in my lab involves the biodiversity of Kimball Creek, a 3rd-order stream near De Beque, Colorado. Like many western streams, Kimball Creek has experienced in-stream channel and riparian habitat degradation due to historic land use practices, including heavy cattle grazing, the creation of diversion dams for irrigation, and the extirpation of beaver. These disturbances, exacerbated by high flows from spring storms and snow melt, have resulted in deeply incised channel morphology and increased sedimentation. Plans are being implemented by the High Lonesome Ranch (HLR), which owns access to the majority of the stream, to restore Kimball Creek to a more natural hydrological pattern and eventually a native cutthroat trout (Oncorhynchus clarkii pleuriticus) fishery. Through extensive monitoring and numerous experiments, we are providing the science necessary to better understand how to manage Kimball Creek, assisting in the planning for the restoration effort, and providing the background data required to evaluate the success of the restoration. As part of this effort, we are building upon existing HLR research by studying trophic cascades within streams and riparian areas, as a way of exploring the ecological effects of restoration of native and threatened species as well as promoting the restoration of biodiversity to these wetlands.
Fig. 2: Scot Peterson (left), a Watershed Science graduate student, sampling Kimball Creek with the assistance of Tom Anderson (right), a graduate of the Watershed Science program that worked as a technician on the project during 2011.
Impacts of Toxicants on Development, Life History, and Population Growth
Another major research effort in my lab has been to understand the ecotoxicology of amphibians. Because of their permeable skin and aquatic lifestyle, many amphibians are particularly susceptible to environmental toxicants from industrial and agricultural sources, and these pollutants may play an important direct or indirect role in amphibian population declines and extinctions.
Fig. 4: Julia Earl, a former graduate student in my lab, working on the effects of pulsed nitrate on amphibian development.
Students in my lab have determined that nitrate has the potential to be an important stressor to amphibian development and growth, (Meredith and Whiteman 2008, Earl and Whiteman 2009; Fig. 4). Although most toxicity tests investigate constant concentrations, concentrations of many compounds in the environment are dynamic, and individuals may be more sensitive to pulses of a chemical initiated at specific points during development (e.g., after fertilizer is sprayed on fields). Using a series of experiments with constant versus pulsed concentrations of nitrate in Hyla chrysoscelis (gray tree frog) tadpoles, we found that nitrate has subtle but important effects at low doses, and that species may be better able to deal with pulses that occur early rather than late in development (Earl and Whiteman 2009). A greater understanding of the effects of such pulses may help conservation biologists to manage populations and prevent population declines. Currently we are expanding this research to consider the role of pesticides on amphibian development, reproductive behavior, and population growth in a variety of species and life stages.
Effects of Invasive Species Management on Biodiversity
The impacts of invasive species on native flora and fauna have become increasingly evident over the past few decades. Common reed (Phragmites australis; Fig. 5) is an aquatic plant native to the United States that has successfully invaded numerous wetland habitats beyond its native range, and foreign strains of this species have also been introduced. Phragmites has been implicated in dramatic habitat changes, causing shifts in plant and animal communities. Aerial herbicide spraying of Phragmites is considered effective for population control, but herbicides can have unforeseen consequences toward non-target organisms and ecosystem processes. Few studies have determined the effects of Phragmites eradication on wetland animal communities, although species such as fish, reptiles, and amphibians are likely to be affected, due to susceptibility to toxicants, dependence on wetland habitats, and/or limited dispersal.
Fig. 5: Phragmites australis at the CCWMA.
Phragmites is particularly innocuous at the Clear Creek WMA (CCWMA; Hopkins County, KY; Fig. 6) where it dominates the landscape, has likely altered wetland hydrology, and has caused numerous access problems. Several threatened species that are susceptible to aquatic toxicity inhabit Clear Creek, and may also be affected by large-scale Phragmites removal. However, no studies had been conducted to determine the effects of large scale Phragmites eradication on these and other species. The goal of this study is to understand the effects of Phragmites management on threatened species, as well as fish, amphibian, and reptile diversity, using an experimental (sprayed) site and two control sites: one with Phragmites, and one without.
Fig. 6: CCWMA (green outline) showing dead Phragmites in the experimental treatment (light red color). Sampling sites are noted by triangles. EX = Phragmites experimental sites; DC = Phragmites control sites.
Using a variety of sampling techniques, we have sampled these three sites repeatedly since July 2009. Thus far, we have recorded several species of conservation concern within the CCWMA, including western lesser sirens (Siren intermedia), bird-voiced treefrogs (Hyla avivoca), copperbelly water snakes (Nerodia erythrogaster neglecta), diamondback watersnakes (Nerodia rhombifer rhombifer), western cottonmouth (Agkistrodon piscivorus leucostoma), the lake chubsucker (Erimyzon sucetta), American black duck (Anas rubripes), the least bittern (Ixobrychus exilis), great egrets, (Ardea alba), solitary sandpiper (Tringa solitaria) and the American bittern (Botaurus lentiginosus). Although we currently have no evidence that herbicide spraying has impacted biodiversity either positively or negatively, monitoring will continue at least through 2011.
We are performing several additional studies to understand the potential impacts of Phragmites invasion and management on SGCN and the CCWMA ecosystem. We are conducting an in-depth study of lake chubsucker diet and electivity in each study site to detect the potential for cascading effects of herbicide management on the invertebrate and fish community. We are also analyzing stable isotopes throughout the CCWMA food web to detect the implications of the death of a dominant wetland plant on ecosystem function (e.g., nutrient cycling and energy flow). Finally, we are analyzing Phragmites genotypes to better understand its origin (i.e., native to North America or elsewhere).
Because removing Phragmites via herbicide spraying is a critical management goal with unknown consequences toward the CCWMA environment and the species within it, our project will be an important step in understanding the ecological effects of removing Phragmites from wetlands where it dominates, and of utilizing herbicides for such manipulations. By understanding the effects of this management on biodiversity at Clear Creek, wildlife biologists will have the necessary insight to prescribe future Phragmites removal at this sites across the world.
Other Conservation Research
Students in my laboratory are currently involved in two other projects, both located within the Land Between the Lakes (LBL) National Recreation Area. First, students are studying a captive population of elk at the Elk and Bison Prairie (EBP). This population has been critical to the successful reintroduction of elk in the eastern U.S., yet few studies have focused on the ecological or behavioral consequences of the elk reintroduction. Currently we are evaluating both the genetic diversity of this herd and determining how elk and deer browsing behavior might influence plant communities in areas where elk are reintroduced. Future studies will explore the breeding behavior of this population and its impact on reintroduction success. Second, students are exploring the effects of fire management on herpetofaunal diversity. LBL has an active fire management program, and research beginning in 2011 will explore how this management had affected the abundance and diversity of amphibians and reptiles.
Fig. 8: Life cycle of tiger salamanders at the Mexican Cut Nature Preserve
Historically, much of my research has involved the evolution of alternative life histories in salamanders. In some salamander species, individuals either transform from an aquatic larval stage into a terrestrial "metamorphic adult", or they remain within the aquatic environment as a sexually mature "paedomorphic adult" (Fig. 7). This dimorphism, called facultative paedomorphosis, is environmentally induced (and thus a polyphenism) because environmental conditions experienced as a larva influence whether an individual becomes one morph or the other (Fig. 8).
Fig. 7: Metamorphic (top) and paedomorphic (bottom) tiger salamanders.
In 1994 I proposed three hypotheses for the maintenance of facultative paedomorphosis (Whiteman 1994). A literature review revealed that at least two of the three mechanisms are operating in natural populations, suggesting that selection can favor the production of the same adaptive polymorphism for very different evolutionary reasons. Using two species of salamanders, I have been testing these and other hypotheses, and exploring the ecological and evolutionary mechanisms that produce and maintain paedomorphosis.
Much of this work has been conducted on the tiger salamander, Ambystoma tigrinum nebulosum. Over the past 21 years, I have followed a marked population of this species at the Mexican Cut Nature Preserve in Colorado. This research supports the idea that selection pressures in the Rocky Mountains maintain paedomorphosis through very different evolutionary processes than those that maintain the dimorphism at lower elevations or in other species (Whiteman et al. 1995, 1996, Denoel et al. 2007), and that multiple mechanisms can produce the same adaptive morphology in the same population (Wakano and Whiteman 2008, Whiteman et al. in review). Besides confirming the existence of alternative selection mechanisms for the production of paedomorphosis, these results suggest that plasticity in one trait or suite of traits can be adaptive for very different evolutionary reasons in the same population, or across different populations or species. My Colorado research has also shown that sex plays a strong role in the payoffs to each morph, and may also influence the degree to which members of each sex become a certain morph (Whiteman 1997, Whiteman et al. in review). This result suggests that other polymorphisms and plastic responses may also have sex-specific payoffs that have been thus far unappreciated.
Fig. 9: Experimental mesocosms used to manipulate amphibian populations at the Hancock Biological Station
A parallel system to my Colorado research occurs in mole salamanders, Ambystoma talpoideum. Mole salamanders, unlike montane populations of tiger salamanders, live in low-elevation Carolina bays and other wetlands of the southeastern U. S. Thus, the environments experienced by these two species are extremely different, and provide an interesting comparison. My students have been manipulating this species in mescosm experiments (Fig. 9) to understand the effect of environmental variation on morph production and fitness differences. Thus far, we have found the first experimental evidence that paedomorphs can be produced through two disparate mechanisms in the same population (Doyle and Whiteman 2008), and that both predation and interspecific competition in the early stages of development can have significant effects on adult life history (Landolt 2009, Anderson 2011).
Current research on this system is aimed at evaluating the fitness consequences of polyphenism using microsattelite markers, and understanding the effects of size-structure on morph production and fitness.
Anderson, T. A. 2011. Experimental and observational approaches to assess competition in
larval salamanders. M.S. Thesis, Murray State University.
Bohonak, A. J. and H. H. Whiteman. 1999. Dispersal of the fairy shrimp Branchinecta coloradensis (Anostraca): Effects of hydroperiod and salamanders. Limnology and Oceanography 44:487-493.
Earl, J. E. and H. H. Whiteman. 2009. Effects of pulsed nitrate exposure on amphibian
development. Environmental Toxicology and Chemistry 28:1331-1337.
Denoel, M., H. H. Whiteman, and S. A. Wissinger. 2007. Optimality of foraging tactics in
alternative heterochronic morphs. Freshwater Biology 52:1667-1676.
Doyle, J. and H. H. Whiteman. 2008. Paedomorphosis in Ambystoma talpoideum: Effects of
initial size variation and density. Oecologia 156:87-94.
Landolt, K. N. 2008. Predator presence in the facultatively paedomorphic mole salamander,
Ambystoma talpoideum. M.S. Thesis, Murray State University.
Meredith, C. S. and H. H. Whiteman. 2008. Effects of nitrate on embryos of three
amphibian species. Bulletin of Environmental Contamination and Toxicology 80:529-
Wakano, J. Y. and H. H. Whiteman. 2008. Evolution of polyphenism: the role of density and
relative body size in morph determination. Evolutionary Ecology Research 10:1157-1172.
Whiteman, H. H. 1994. Evolution of facultative paedomorphosis in salamanders. Quarterly Review of Biology 69:205-221.
Whiteman, H. H., S. A. Wissinger, and A. J. Bohonak. 1995. Seasonal movement patterns in a high-elevation population of the tiger salamander, Ambystoma tigrinum nebulosum. Canadian Journal of Zoology 72:1780-1787.
Whiteman, H. H., S. A. Wissinger, and W. S. Brown. 1996. Growth and foraging consequences of facultative paedomorphosis in the tiger salamander, Ambystoma tigrinum nebulosum. Evolutionary Ecology 10: 429-442.
Whiteman, H. H. 1997. Maintenance of polymorphism promoted by sex-specific fitness payoffs. Evolution 51:2039-2044.
Whiteman, H. H. and S. A. Wissinger. 2005. Multiple hypotheses for population fluctuations: the importance of long-term data sets for amphibian conservation. In: M. L. Lanoo (ed.), Status and Conservation of U.S. Amphibians, California University Press.
Wissinger, S. A. and H. H. Whiteman. 1992. Fluctuation in a Rocky Mountain population of
salamanders: anthropogenic acidification or natural variation? Journal of Herpetology 26:377-391.
Wissinger, S. A., A. J. Bohonak, H. H. Whiteman, and W. S. Brown. 1999a. Subalpine wetlands in Colorado: Habitat permanence, salamander predation and invertebrate communities. In: Bazter, D. P., R. B. Rader, and S. A. Wissinger (eds.), Invertebrates in Freshwater Wetlands of North America: Ecology and Management. John Wiley and Sons.
Wissinger, S. A., H. H. Whiteman, G. L. Rouse, G. B. Sparks, and W. S. Brown. 1999b. Foraging trade-offs along a predator-permanence gradient in subalpine wetlands. Ecology 80:2102-2116.
Wissinger, S. A., H. H. Whiteman, M. Denoel, M. L. Mumford, and C. B. Aubee. 2010.
Consumptive and non-consumptive effects of inter-cohort cannibalism in an age-structured population. Ecology 91:549-559.