Environmental degradation caused by human activities is one of the greateast threats to amphibians and has at least contributed to -- if not been responsible for -- observed decline of amphibian populations. Much of the United States has experienced dramatic development and landscape changes during the past century. Vast areas of forest have been cleared and wetland drained and filled for human occupation and use. The remaining terrestrial and wetland habitats are often small and disjunct or polluted. In the New England area, primarily two conservation issues are of particular concern: habitat fragmentation and acid deposition.

• HABITAT FRAGMENTATION

  Lands converted to human uses are characteristically dry, open and inhospitable to amphibians because amphibians are generally slow-moving, small-bodied, and physiologically constrained to remain near moist refugia (Gibbs 1998b). When the forest habitat of a metapopulation of Notophthalmus viridescens becomes fragmented, being subdivided into smaller parcels by roads, houses and other anthropogenic features that are unsuitable habitats or dispersal barriers, poplations at the local level become isolated, the effective population size dwindles, and each small, local population is predisposed to local extinction due to amplified local environmental variation and demographic stochasticity.

  Investigating distribution of woodland amphibians along a forest fragmentation gradient in New Haven County, Connecticut, Gibbs (1998a) found that the initially and naturally low population density of Notophthalmus viridescens (as compared to those of other woodland amphibians) apparently predisposed Red-spotted Newts to population collapse associated with habitat fragmentation. Populations did not persist below a forest cover threshold of about 50%. A higher initial density would translate into larger effective population size in each habitat fragment, which may buffer fragmented populations against local extinction. Furthermore, perhaps surprisingly, dispersal ability was found to be inversely related to fragmentation resistance (Gibbs 1998a), and the Red-spotted Newt -- with a life stage dedicated to dispersal and more drought tolerant than most other amphibian species -- was found in another study to exhibit edge-avoidance behavior (Gibbs 1998b). Gibbs (1988a) reasoned that, in heavily forested areas, having a large proportion of the population dedicated to dispersal likely facilitates colonization of new ponds. In fragmented habitats, however, most dispersing efts likely end their explorations in unsuitable habitats or become stranded in open habitats between forested areas. Hence, a high dispersal tendency that may represent a valuable trait in Notophthalmus viridescens for exploiting ephemeral breeding ponds in unfragmented habitats (Gill 1978) may become a liability when the environment becomes fragmented.

• HABITAT ACIDIFICATION

  Acidification of the environment occurs largely from atmospheric deposition of the products of fossil fuel combustion such as sulfur oxides and nitric oxides. Among the more important effects of acidification of the aquatic environment on amphibians is reduced hatching of eggs and reduced rates of growth, setting the stage for increased losses due to predation (Diana & Beasley 1998). In a simulated pond study including variations on a model community representative of those found in local temporary ponds, Sadinski & Dunson (1992) found that significantly fewer larval newts survived in pH 4.2 compared to in pH >6. It is not clear whether this was due to embryonic or larval intolerance of pH 4.2 or reduced prey availability. Data on the tolerance of embryos or larvae of Red-spotted Newts to low pH have yet to emerge. Sadinski & Dunson (1992) also observed significantly more adult newts leaving pools of pH 4.2 than pH >6. This behavioral response to pH 4.2 could have been a consequence of physiological intolerance (Frisbie & Wyman 1992, see below) or reduced availability of food in pools of pH 4.2.

  One complication that amphibians experience as a consequence of reduced ambient pH is an increased loss of body sodium. Exposure to acid inhibits active uptake of sodium and stimulates passive loss via diffusion (Robinson 1993). Frisbie & Wyman (1992) examined the effects of exposure for 48 hours to pH 3 and pH 5 on sodium balance of adults and efts of Notophthalmus viridescens in an aquatic setting, and observed that both adults and efts experienced net sodium loss at pH 3 but not 5. However, sodium balance in Notophthalmus viridescens appears to be less affected by low pH than that in other amphibians, apparently because the newts exhibit a pattern of resistance to elevated sodium efflux when exposed to low pH (Wyman 1988, Frisbie & Wyman 1992, Robinson 1993). Robinson (1993) also found that Eastern Newts chronically exposed to low-pH conditions are able to recover their ion balance, most likely by a combination of compensatory measures, including stimulation of cutaneous sodium uptake and inhibition of sodium loss by cutaneous and/or renal pathways. This provides the newts with an unusual capacity to withstand more acidic conditions than other amphibian speices.

  A major concern regarding acidification of the environment is the increased aluminum toxicity. Aluminum is among the most abundant mineral constituents of natural soils. Acid precipitation and low pH can alter the speciation of aluminum, thereby increasing its toxicity. Especially important is the tendency for acidification to increase the formation of inorganic monomeric aluminum, an extremely toxic form of the metal (Diana & Beasley 1998). However, no information is available on the susceptibility of Eastern Newts to aluminum.