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Ambystoma tigrinum (Green, 1825)
Tiger
Salamander
Michael J. Lannoo
1. Historical versus Current Distribution. Tiger salamanders
(Ambystoma tigrinum) are the most widespread salamander species in
North America. They occur along the Atlantic and Gulf Coastal Plains from Long
Island, New York, to southeastern Louisiana and north into Mississippi, Alabama,
Tennessee, and Kentucky. They are found throughout the Midwest, Great Plains, the
eastern Front of the Rocky Mountains, and on the Columbia Plateau. Disjunct
populations occur both in western and in Appalachian states. References to tiger
salamander distributions include Engelhardt (1916a,b), Duellman (1955), Rossman (1965a),
Cook (1957), Smith (1961), Cliburn (1965), Barbour (1971), Hudson (1972), Minton (1972,
2001), Harris (1975), Mount (1975), Hodge (1976), Williamson and Moulis (1979), Harker
et al. (1980), Martof et al. (1980), DeGraaf and Rudis (1981, 1983), Vogt (1981), McCoy
(1982), Hammerson (1986, 1999), Dixon (1987, 2000), Green and Pauley (1987), Pearson et
al. (1987), Ashton and Ashton (1988), Bury and Corn (1988b), Black and Sievert (1989),
Dundee and Rossman (1989), Hoberg and Gause (1989), Pfingsten and Downs (1989),
Christiansen and Bailey (1991), Gibbons and Semlitsch (1991), Harding and Holman (1992),
Hulse and Hulse (1992), Johnson (1992), Collins (1993), Klemens (1993), Leonard et al.
(1993), Nussbaum et al. (1983), Oldfield and Moriarty (1994) McAllister (1995), Redmer
and Ballard (1995), Casper (1996, 1997), Degenhardt et al. (1996), Esco and Jensen
(1996), Killebrew et al. (1996), Redmond and Scott (1996), Blair et al. (1997), Dvornich
et al. (1997), Luce et al. (1997), Oliver (1997), Brodman and Kilmurry (1998), Brodman
(1999a), Kunzmann and Halvorson (1998), Petranka (1998), Petzing et al. (1998),
Pfingsten (1998a), Arizona Game and Fish Department (1999a,b), Bartlett and Bartlett
(1999a), Fischer et al. (1999), Livo et al. (1999), McLeod (1999), Maxell (1999),
Mitchell and Reay (1999), Nevada Natural Heritage Program (1999), Phillips et al.
(1999), and Andrews (2000). Altitudinal variation extends from sea level to >
3,300 m (Gehlbach, 1967a).
Six subspecies are
currently recognized (Crother et al., 2000; see Petranka, 1998 for subspecies
distribution maps): gray tiger salamanders (A. t. diaboli
Dunn, 1940), barred tiger salamanders (A. t. mavortium Baird,
1850), blotched tiger salamanders (A. t. melanosticum Baird,
1860, see Beltz, 1995), Arizona tiger salamanders (A. t.
nebulosum Hallowell, 1952), Sonoran tiger salamanders (A. t.
stebbensi Lowe, 1954), and eastern tiger salamanders (A. t.
tigrinum Green, 1825). There has been disagreement about whether or not
tiger salamander subspecies deserve separate species status (Collins et al., 1980;
Pierce and Mitton, 1980; Routman, 1993; Templeton et al., 1995; Shaffer and McKnight,
1996) and whether or not populations deserve subspecies status (Dunn, 1940; Gehlbach,
1967a; Jones and Collins, 1992; Jones et al., 1988, 1995). For descriptions of
subspecies see Bishop (1941a), Collins (1981), Gehlbach (1967a), Lowe (1954), Stebbins
(1985), Shaffer and McKnight (1996), Conant and Collins (1998), Petranka (1998), and
Larson et al. (1999).
The current
distribution of tiger salamanders differs from the historical distribution. Many
populations within the historical distribution have been extirpated (e.g., Lannoo et
al., 1994; Lannoo, 1996). Some extralimital populations, especially in the
southwestern United States, have become established through activities associated with
the fish bait industry (e.g., Carpenter, 1953; Espinoza et al., 1970; Collins et al.,
1988; Lannoo, 1996; Petranka, 1998). The overall pattern is fragmentation and loss
of populations within their historical distribution, with sporadic, anthropogenically
assisted invasions of new habitats.
2. Historical versus Current Abundance. While remaining locally common in many
regions, tiger salamander numbers have plummeted compared with historical levels (e.g.,
Lannoo, 1996). Lannoo et al. (1994) suggest that numbers of amphibians, including
tiger salamanders, on the landscape have decreased more rapidly than has habitat loss,
and in portions of the Midwest, EuroAmerican settlement has produced nearly 99% habitat
(breeding wetland) loss (Leja, 1998).
Corn and Vertucci
(1992) describe the role of acid rain in western tiger salamander declines. Larson
(1998) examines the possible effect of agricultural pesticides in endocrine disruption
in tiger salamanders.
Over a 7-yr period
during the 1980s, Harte and Hoffman (1989) demonstrated a 65% decline in tiger
salamander adults that led to a decline in larval recruitment. During the 1980s
and early 1990s Semlitsch et al. (1996) demonstrated a similar decline at the Savannah
River Ecology Laboratory (see also Petranka, 1998). Pechmann et al. (1991) and
Wissinger and Whiteman (1992) address the problem of discerning natural population
fluctuations from actual declines.
3. Life History Features.
A. Breeding.
Breeding is aquatic.
i. Breeding migrations. From
upland overwintering sites to breeding wetlands. These migrations typically take
place in March in Iowa, earlier in southern and coastal populations, and later in
northern populations (Bishop, 1941a; Stine et al., 1954; Cooper, 1955; Gentry, 1955;
Brandon and Bremer, 1967; Hassinger et al., 1970; Anderson et al., 1971; Peckham and
Dineen, 1954; Seale, 1980; Morin, 1983a; Semlitsch, 1983a; Lannoo and Bachmann, 1984a;
Downs, 1989g; Trauth et al., 1990; Lannoo, 1996). Migrations are triggered by
warm spring rains and typically occur within a few weeks of ice-off in northern wetlands
(Sever and Dineen, 1978; Semlitsch and Pechmann, 1985; Lannoo, 1996, 1998a).
Males migrate to
breeding sites earlier than females. Semlitsch (1983a) reported males migrated
2–8 wk earlier than females on at the Savannah River Ecology Laboratory
site. This temporal separation is reduced at northern latitudes. Peckham
and Dineen (1954) report that males and females arrive at about the same time at an
Indiana site. Males tend to stay longer than females. Following breeding,
Semlitsch (1983a) reported that one tagged male moved 162 m to an upland site and
returned to the same site to breed the following autumn (see also Petranka, 1998).
While Sever and
Dineen (1978) report that females breed annually, Pechmann et al. (1991) and Semlitsch
et al. (1996) observed substantial variation in the number of breeding adults at Rainbow
Bay on the Savannah River Ecology Laboratory site. Males tend to outnumber
females at breeding sites, with reported male:female ratios ranging from 1:1–5.3:1
(Peckham and Dineen, 1954; Sever and Dineen, 1978; Semlitsch, 1983a).
Breeding times vary
among morphotypes within populations. Rose and Armentrout (1976) report that
large barred tiger salamander morphs breed from January–May, but small morphs will
breed at any time of the year following sufficient rains.
Breeding populations
are known to vary in size (Pechmann et al., 1991). An Indiana population has been
estimated to consist of between 1,100–2,000 adults (Peckham and Dineen, 1954;
Sever and Dineen, 1978; see also Petranka, 1998). In a New Jersey population, 540
breeding animals were counted (Hassinger et al., 1970; Anderson et al., 1971).
ii. Breeding habitat. Seasonal,
semipermanent, and fishless permanent wetlands (Bishop, 1943; Blair, 1951c; Woodbury,
1952; Carpenter, 1953; Smith, 1961; Minton, 1972, 2001; Brandon and Bremer, 1967;
Werner and McPeek, 1994; Lannoo, 1996; see also Petranka, 1998). Tiger salamanders
will also breed in roadside ditches, quarry ponds, cattle tanks, subalpine lakes, and
sluggish streams (e.g., Leonard and Darda, 1995; Petranka, 1998).
B. Eggs.
i. Egg deposition sites. Eastern
tiger salamanders lay eggs in clusters attached to aquatic substrates such as the stems
of emergent vegetation and larger detritus including submerged twigs and branches.
The remaining subspecies lay eggs singly, in small clusters, or in strings.
Diameters of ova are 2–3 mm (Hamilton, 1948; Collins et al., 1980; Kaplan,
1980a).
ii. Clutch size. Numbers of
eggs/cluster from a number of geographically distinct populations ranged from an average
of 38–59 eggs/mass (ranges from 5–122; Bishop, 1941a, 1943; Stine et al.,
1954; Hassinger et al., 1970; Anderson et al., 1971; Morin, 1983a; Trauth et al.,
1990).
Tiger salamanders
show a wide range of clutch sizes, from an average of 421 ova reported in an eastern
tiger salamander population from Michigan (Wilbur, 1977c) to 7,631 eggs from neotenic
barred tiger salamander adults from Texas (Rose and Armentrout, 1976; see also Petranka,
1998).
Incubation times for
eastern tiger salamanders range from 19–50 d, depending on water temperatures
(Engelhardt, 1916b; Bishop, 1943; Stine et al., 1954; Sever and Dineen, 1978; Couture
and Sever, 1979; Morin, 1983a; Trauth et al., 1990). Incubation times for barred
tiger salamanders are 8.5 d at 25 ˚C (Webb and Rouche, 1971; see also Petranka,
1998). Incubation times for Arizona tiger salamanders range from 6.5 d at 19
˚C and between 14–21 d at a natural wetland (Tanner et al., 1971; see also
Petranka, 1998).
Hatchlings are
9–10 mm TL for barred tiger salamanders (Webb and Rouche, 1971), 9–14 mm for
Arizona tiger salamanders (Tanner et al., 1971), and 13–17 mm for eastern tiger
salamanders (Bishop, 1941a; see also Petranka, 1998).
C.
Larvae/Metamorphosis.
i. Length of larval stage. Growth
rate, length of larval period, size at metamorphosis, and duration of metamorphosis vary
with environmental factors such as temperature, food level, salamander density, the
presence of competitors, and wetland persistence (Wilbur and Collins, 1973; Bizer, 1978;
Brunkow and Collins, 1996; Lannoo, 1996).
The larval stage
lasts a minimum of 10 wk but can last longer, even within populations (Engelhardt,
1916a; Bishop, 1943; Stine et al., 1954; Hassinger et al., 1970; Sever and Dineen,
1978; Sexton and Bizer, 1978; Seale, 1980; Lannoo and Bachmann, 1984a; Trauth et al.,
1990). Larvae inhabiting permanent wetlands can overwinter and metamorphose the
following spring (Brandon and Bremer, 1966; unpublished observations). These
animals tend to be sexually immature. Larvae may reach sexual maturity
(technically becoming neotenic; see Larson et al., 1999 for a discussion) and
metamorphose or not depending on a combination of genetic and environmental factors
(Hensley, 1964; Larson, 1968; Dodson and Dodson, 1971; Tanner et al., 1971; Sexton and
Bizer, 1978; Collins et al., 1980, 1988; Jones et al., 1993; Larson et al., 1999).
Size at
metamorphosis varies from 49–75 mm SVL and may be considerably larger (≤ 150 mm
SVL) in animals transforming after reaching sexual maturity (Dundee, 1947; Carpenter,
1953; Gehlbach, 1965, 1967b; Rose and Armentrout, 1976; Sever and Dineen, 1978; Lannoo
and Bachmann, 1984a; see also Petranka, 1998).
Tiger salamander
larvae grow faster than larvae of all other Ambystoma species (Webb and Rouche,
1971; Rose and Armentrout, 1976; Keen et al., 1984; see also Petranka, 1998).
ii. Larval requirements.
a. Food. Tiger salamander larvae are gape-limited,
size selective feeders. They remain size selective in the absence of visual and
olfactory cues, suggesting that nocturnal feeding is mediated by lateral line
mechanoreceptive and electroreceptive organs (Lannoo, 1986, 1987). Larvae are
generalists, feeding on a wide range of invertebrate prey items including zooplankton,
ostracods, aquatic insect larvae and adults, mollusks, oligochaetes, leeches, and
crayfish, as well as anuran tadpoles, small fishes, and conspecifics (Little and
Keller, 1937; Gehlbach, 1965; Black, 1969b; Buchli, 1969; Dodson, 1970; Dodson and
Dodson, 1971; Wilbur, 1972; Rose and Armentrout, 1976; Sever and Dineen, 1978; Brophy,
1980; Zaret, 1980; Collins and Holomuzki, 1984; Lannoo and Bachmann, 1984a; Leff and
Bachmann, 1986; Holomuzki and Collins, 1987; Zerba and Collins, 1992; Brunkow and
Collins, 1996). Smaller larvae eat smaller prey. While larger larvae eat
larger prey, they will also air gulp to fill their lungs and acquire buoyancy
("stratify" sensu Branch and Altig, 1981; see also Lannoo and Bachmann, 1984b)
and feed on pelagic zooplankton (Rose and Armentrout, 1976; Lannoo and Bachmann, 1984b)
and other smaller prey (Lee and Franz, 1974; Brophy, 1980; Tyler and Buscher,
1980). The kinematics of prey capture by Ambystoma larvae were described
by Hoff et al. (1985), Shaffer and Lauder (1985), and Reilly et al. (1992).
Cannibal morph
larvae occur in tiger salamanders (see "Larval polymorphisms" below).
Cannibal morphs tend to eat larger prey than typical morphs. In populations of
barred tiger salamanders, cannibal morphs may preferentially take conspecifics (Rose
and Armentrout, 1976; Collins and Holomuzki, 1984; Holomuzki and Collins, 1987; Pfennig
et al., 1994; Whiteman et al., 2003), while cannibal morph eastern tiger salamanders
take conspecifics as a component of a generally broader diet (Lannoo and Bachmann,
1984a; Loeb et al., 1994). Large typical larvae may also be cannibalistic (Crump,
1983; Lannoo et al., 1989).
The diets of
neotenic adults generally resemble that of large larvae (Sprules, 1972; Norris,
1989).
b. Cover. Larvae move vertically and horizontally
within wetlands. Horizontal diel movements are thought to be related to
temperature regulation (Prosser, 1911; Whitford and Massey, 1970; Heath, 1975; Holomuzki
and Collins, 1983; Holomuzki, 1989b; see also Petranka, 1998). Larvae show site
preferences, moving to the same general vicinity of the littoral zone every day
following nocturnal migrations to deeper water (Gehlbach, 1967b; see also Petranka,
1998). Causes underlying vertical migrations are more complicated. Collins
and Cheek (1983) and Holomuzki (1989b) observed larvae moving into the open water,
pelagic zone, during the day and retreating to the pond bottom at night. These
movements are thought to be related to thermoregulation and/or predator (dytiscid
beetle) avoidance. Tiger salamander larvae, similar to other wetland-dwelling
Ambystoma, migrate off the bottom and into the pelagic zone at night to feed on
zooplankton (Anderson and Graham, 1967; Branch and Altig, 1981; Brophy, 1980; Lannoo and
Bachmann, 1984b).
iii. Larval polymorphisms.
Cannibal morphs, animals with proportionally large heads and large teeth, have been
reported in nature from three of the six tiger salamander subspecies: barred tiger
salamanders, Arizona tiger salamanders, and a single metapopulation of eastern tiger
salamanders from northwestern Iowa (Powers, 1907; Rose and Armentrout, 1976; Lannoo and
Bachmann, 1984a; Pierce et al., 1981, 1983; Reilly et al., 1992; Whiteman et al., 2003;
see also Larson et al., 1999). Cannibal morphs in Sonoran tiger salamanders and in
eastern tiger salamanders from Indiana have been induced in the laboratory (J.P. Collins
and D. Pfennig, respectively, personal communication; see also Larson et al.,
1999).
In nature,
populations with the genetic capacity to express cannibal morphs may not do so every
year (Collins and Cheek, 1983; Lannoo and Bachmann, 1984a; Pfennig et al., 1991).
In these populations, conspecific density appears to trigger the expression of cannibal
morphs (Collins and Cheek, 1983; Lannoo and Bachmann, 1984a; Pfennig et al., 1991, 1994;
Pfennig and Collins, 1993; Maret and Collins, 1994).
Interestingly, the
tooth morphology differs between cannibal morphs from eastern and barred tiger
salamander populations, suggesting either separate evolutionary inventions or
divergence from a common ancestor (Larson et al., 1999). Intermediate forms
between cannibal and typical morphs appear under conditions that produce fully developed
cannibal morphs (Pedersen, 1993; Larson et al., 1999).
iv. Features of metamorphosis.
Metamorphosis can, but does not always, involve large numbers of individuals (M.J.L.,
personal observations). Semlitsch (1983a) noted that numbers of newly
metamorphosed animals/breeding female ranged from 0–24.
v. Post-metamorphic migrations.
From breeding wetlands to upland sites. In some populations newly metamorphosed
animals remain near wetlands, in others they migrate some distance. The longest
recorded distance moved from a wetland is 229 m (Gehlbach, 1967b). These
emigrations tend to occur during rainy nights (Sever and Dineen, 1978; personal
observations); when wetlands occur near highways, mortality can be high (Duellman,
1954a; Lannoo, 1996).
vi. Neoteny. Known in eastern
tiger salamanders from populations in Michigan (Hensley, 1964; Larson, 1968; Collins et
al., 1980; Jones et al., 1993), Wisconsin (G.S. Casper and M. Mossmann, personal
communication), Illinois (Whiteman et al., 1998), and in each of the western subspecies
(Powers, 1903; Burger, 1950; Glass, 1951; Knopf, 1962; Buchli, 1969; Sprules, 1974a;
Wiedenheft, 1983; Whiteman, 1994c; Whiteman and Howard, 1998; Petranka, 1998; Larson et
al., 1999; see also Gould, 1977). A neotenic, cave dwelling population of tiger
salamanders occurs in New Mexico (Thompson and Jones, 1992).
D. Juvenile
Habitat. Juveniles may remain in or near wetlands to feed or may migrate to upland
sites and burrow.
E. Adult
Habitat. Tiger salamander adults occupy a wide variety of habitats, from the moist
lowland coastal plains of the southeastern United States to the arid Great Plains,
desert southwest, and altitudes in the Rocky Mountains (Burger, 1950; Gehlbach, 1969;
Webb, 1969; Webb and Rouche, 1971). Tiger salamanders are tolerant of agriculture
(but see Larson, 1998) and are the most common salamanders throughout the Midwest.
They tend to be associated with grasslands, savannas, and woodland edges, and less so
with forests.
Adult tiger
salamanders can be terrestrial or aquatic (neotenic). Terrestrial adults burrow
and require deep friable soils. Tiger salamanders actively burrow by using their
forelimbs (Gruberg and Stirling, 1972; Semlitsch, 1983c). Animals tend to live near
the surface (12 cm deep; Semlitsch, 1983b) but can be found deeper; Gehlbach (1965)
found an animal 2 m below the soil surface. Other animals often live in or are
associated with mammal burrows and are active on the surface during rainy nights
(Hamilton, 1946; Calef, 1954; Duellman, 1954a; Carpenter, 1955; Gehlbach, 1967a; Collins
et al., 1993).
Aquatic, neotenic
adults generally require fishless permanent wetlands, where they are the top aquatic
carnivores. These animals are threatened during droughts and may or may not be
able to metamorphose; with increasing age, neotenic adults become less able to
transform.
F. Home Range Size.
Unknown for either terrestrial or neotenic adults.
G.
Territories. Territories have not been documented in either terrestrial or
neotenic adults.
H.
Aestivation/Avoiding Dessication. During dry conditions, terrestrial tiger
salamanders can burrow deeper into moister soil. One tiger salamander was found 2 m
below the soil surface (Gehlbach, 1965).
Neotenic adults must
metamorphose to avoid drying wetland conditions. There is no evidence that they
have the capacity to burrow into the mud and aestivate.
I. Seasonal
Migrations. Aside from migrations to and from breeding sites by terrestrial adults
(see "Breeding migrations" and "Post-metamorphic migrations" above),
no other migrations have been documented.
J. Torpor
(Hibernation). Terrestrial adults overwinter by burrowing below the frost
line. Aquatic adults overwinter in permanent, sometimes in semi-permanent, bodies
of water.
K. Interspecific
Associations/Exclusions. Predation by neotenic adults eliminates or controls
cladocerans (Daphnia pulex), fairy shrimp (Branchinecta
shantzi), and other invertebrates in subalpine lakes in Colorado (Sprules,
1972; see also Petranka, 1998) and arid wetlands (Holomuzki et al., 1994). Tiger
salamander larvae lower survivability of larvae of syntopic Ambystoma, including
blue-spotted salamanders (A. laterale), small-mouthed salamanders
(A. texanum), and Tremblay's salamanders (A.
tremblayi).
Egg mortality by
eastern newts (Notophthalmus viridescens) can be sufficient to exclude
tiger salamanders from wetlands (Morin, 1983a; see also Petranka, 1998). However,
eastern newts and tiger salamanders co-exist in ponds, including in southern Illinois,
where they have similar diets (Brophy, 1980).
L. Age/Size at
Reproductive Maturity. Terrestrial adults can reach 35 mm TL (see also Petranka,
1998), with males either similarly sized or slightly smaller than females. Males
tend to have longer tails. Semlitsch (1983a) noted that 6 of 1,041 marked
postmetamorphic animals returned to breed 2 yr later; 52 were observed the following
year (Glass, 1951).
M. Longevity.
Nigrelli (1954) reports that in captivity, neotenic adults live as long as 25 yr;
terrestrial adults live for 16 yr (see also Petranka, 1998).
N. Feeding
Behavior. Terrestrial adults feed upon a variety of invertebrates associated with
the soil and the soil surface. These include annelids and insect larvae and
adults. Adults are also known to feed on small vertebrates, including field mice
(Peromyscus sp.; Bishop, 1941a) and a hatchling racerunner
(Cnemidophorus selineatus; Camper, 1986). Captive adults will
eat a wider variety of food items, including small frogs, snakes, and lizards
(Duellman, 1948; Camper, 1986), that they may or may not eat in nature (Camper,
1986).
Nonbreeding
terrestrial adults and newly metamorphosed animals will forage in fishless wetlands
(Whiteman et al., 1994; personal observations). Adult barred tiger salamanders
from high elevation ponds can be terrestrial or may move to wetlands to feed.
Terrestrial adults in permanent ponds often move to semi-permanent ponds where
competition is reduced and food density higher (Whiteman et al., 1994; see also
Petranka, 1998).
O. Predators.
A large number of predators are known to feed on tiger salamander eggs, larvae, and
adults, including insects such as caddisflies (Dalrymple, 1970), dragonfly naiads,
predaceous diving beetles (Holomuzki, 1985a,b, 1986a), and giant water bugs; amphibians
such as eastern newts (Morin, 1983a), conspecifics (cannibal morphs and cannibalistic
typical morphs), and marbled salamander (Ambystoma opacum) larvae;
snakes including garter snakes (Thamnophis sp.) and eastern hog-nosed snakes
(Heterodon platirhinos); a variety of predatory birds, shorebirds, and
wading birds including killdeer, bitterns, grackles, loggerhead shrikes (Jensen, 2003),
gray jays, kingfishers, great blue herons, and egrets; mammals including badgers (Long,
1964), bobcats, raccoons, coyotes, opossums, and humans (see also Petranka, 1998).
P. Anti-Predator
Mechanisms. Tiger salamander larvae and neotenic adults exhibit a fast start
movement that permits escape in aquatic environments. Terrestrial adults will
assume a defensive posture by raising their hind legs and arching and waving their tail
(Brodie, 1977; Smith, 1985). As with other Ambystoma species, terrestrial
tiger salamander adults produce secretions from granular skin glands along the dorsal
surface of their tail. These secretions have two components: a sticky component
that adheres to a potential predator and can encumber their movement and a toxic/noxious
component that can repel, even kill, predators (Brodie and Gibson, 1969; Arnold, 1982;
Brodie, 1983; Evans, 1993; Hamning et al., 2000). Hamning et al. (2000)
demonstrate that the adhesive component of these glands is supplied by disulfide
linkages, and that the noxious component is provided by neurotoxins. Hamning et
al. (2000) speculate that at least two neurotoxins are present: one that binds to a
protein, inhibits neurotransmission, and is reversible, and a second that is either a
protease or lipase, causes cellular damage, and is effective over a longer time
period.
Larvae tend to be
nocturnally active in warmer climates and temperatures (see Petranka, 1998), thus
avoiding predation by visual predators. Barred tiger salamander larvae move into
open water at night to avoid being eaten by predaceous diving beetles (Dytiscus
dauricus; Holomuzki, 1986a; see also Petranka, 1998). Small larvae do
not move to areas to avoid larger cannibal morph larvae (Holomuzki, 1986b; Skelly,
1992).
Q. Diseases.
The parasite loads cannibal morph larvae acquire (see "Parasites" below) may
make them more susceptible to disease than typical morphs (Pfennig et al., 1991).
In wetlands, densities of cannibal morphs are inversely related to disease
incidence.
In desert and
grassland populations, epizooic bacteria (Acinetobacter sp.) blooms, perhaps
caused by accumulations of livestock, are thought to be responsible for mass die-offs of
tiger salamanders (Worthylake and Hovingh, 1989). Red-leg outbreaks can occur
under stressful conditions. One outbreak was caused by a zooplankton (prey) crash
following heavy siltation due to a nearby construction project, a failure to erect
erosion fences, and a midwestern thunderstorm—the only year that red-leg disease
has been observed to be pervasive and fatal in this population (M.J.L., personal
observation).
Chytridiomycosis
transmission and pathogenicity in desert populations of tiger salamanders is detailed
by Davidson et al. (2003).
R. Parasites.
Presumably due to their diet of conspecifics, cannibal morph larvae carry more parasitic
nematodes than do typical larvae.
Larvae in some
populations serve as hosts to a large number of leeches, but it is uncertain whether
leeches cause direct mortality (Carpenter, 1953; Holomuzki, 1986c; see also Petranka,
1998).
4. Conservation. As with many amphibian species that breed in semipermanent
wetlands, larval tiger salamanders often experience mass mortality associated with pond
drying (Sever and Dineen, 1978; Lannoo, 1998a). This is a natural
phenomenon. The biggest threat to existing tiger salamander populations comes from
continued wetland destruction and wetland alteration through aquacultural activities
such as those promoted officially by the states of Iowa and Wisconsin (Lannoo et al.,
1994; Lannoo, 1996). Introduced fishes have long been known to reduce or
eliminate tiger salamander populations (Carpenter, 1953; Espinoza et al., 1970; Collins
et al., 1988). To quote Petranka (1998): "The ecological effects of fish
introductions on native amphibians should be carefully considered by fish and wildlife
managers when deciding whether or not to stock natural, fish-free habitats."
According to
Petranka (1998), deforestation is also a problem in southeastern and midwestern
populations. Northeastern populations are affected by acid deposition.
Tiger salamander adults avoid waters with a low pH; at a pH of 4.2, 50% of embryos
suffer mortality (Whiteman et al., 1995). At a low pH, tiger salamanders also
experience reduced growth and longer larval periods (Kiesecker, 1996).
Tiger salamanders
are listed as Endangerd in Delaware, New York, New Jersey, and Maryland; Protected in
Arizona; and Of Special Concern in North Carolina and South Carolina.
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
Citation: AmphibiaWeb: Information on
amphibian biology and conservation. [web application]. 2010. Berkeley, California:
AmphibiaWeb.
Available: http://amphibiaweb.org/.
(Accessed: Sep 2, 2010).
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