California Tiger
Ambystoma tigrinum
Salamander
Adult Reproductive Stage Threats
Habitat Loss
Habitat loss is also an obstacle for salamanders in the reproductive phase and can negatively affect the entire population and its reproductive output. California Tiger Salamanders return to the pond in which they were born once they reach maturity to reproduce. Therefore, destruction of a breeding pond may result in loss of the entire population returning to that site, when the salamander comes home to find nothing left. (Kanner, 2014).
There are many limiting factors in the California Tiger Salamanders reproductive cycle which contribute to the salamander's fragility. At the onset of the winter rains, these salamanders will emerge in the night from their burrows to migrate as far as one mile to their wetland breeding ponds (No Room To Roam, 2015). One study located 95 percent of the salamanders within 2,100 feet of their breeding pond in Solano County. On the way to a reproductive pond, roads and habitat fragmentation pose a deadly threat. Moving at 50 meters an hour, salamanders are not easily seen by cars driving on dark roads during the salamander's nocturnal migration. Many do not survive their journey .
If the salamanders make their journey back to their breeding pond, they are encountered with many different threats. Introduction of non-native Tiger Salamanders might harm populations through hybridization and/or competition. Salamanders face issues finding a partner to reproduce due to habitat fragmentation. Habitat fragmentation prevents gene flow between the populations is prevented. This increases the occurrence of inbreeding, which results in a decrease in genetic variability and the birthing of weaker individuals. Fragmented populations where inbreeding occurs often ends in a genetic bottleneck. This is an evolutionary event where a significant percentage of the population or species is killed or otherwise prevented from reproducing (Kanner, 2014).
Click below to learn more about each threat the tiger salamander faces:
Specific Nesting Requirements - Finding the Perfect Home
The California Tiger Salamander take four to six years to reach reproductive maturity, and after this long period of time, the majority have died off. A female California Tiger Salamander usually breeds only once in her lifetime of up to forty years, and there are only 20 reproducing couples in a given year (Kanner, 2014).
But, when the rains of late winter come, California Tiger Salamanders are drawn out of their burrows to mate. If the Salamanders do make it to the adult phase, in order to reproduce, very specific nesting requirements must be met. This includes knee deep pools for the animals to breed, sufficient amounts of vegetation around the pond, as salamanders lay their eggs attached to vegetation. The salamanders also need 1 square foot per individual to live successfully, so it must be a decently sized ephemeral pools which do not have populations of fish. Tiger Salamanders have very short breeding season. They are explosive breeders, meaning they emerge, breed quickly, and then return to their burrows. They may breed two or three times a year this way. Juveniles migrate from these ponds to underground burrows in the spring during the rains. In years when rainfall is sparse or late, larger proportions of surviving adults, especially females, fail to migrate to breeding ponds (Kanner, 2014). Because of the fact that this species has a high biotic potential, it means that the salamander is facing serious threats. In normal conditions, the California Tiger Salamander's population would be able to bounce back very quickly.
Hybridization Between Native & Nonnative Tiger Salamanders
The problem with hybridization began 60 years ago when commercial bait sellers in California imported millions of nonnative Texas amphibians called barred tiger salamanders whose larvae are excellent bait for fishermen. The adult barred salamanders soon began populating ponds all over Northern California. Although these new salamanders were harmless at first, these invaders quickly mated with the California natives and their hybridized descendants spread all over the state. In a study done of salamanders in California, more than 20 generations of hybridization have resulted in an array of negative effects.
One negative effect is that the hybrid salamanders out-compete the tiny larvae of the native tiger salamanders for food. Because of loss of food and water, the native larvae transformation into full-grown adults is delayed, making the less agile little ones easy prey to the hybrids. Additionally, this study found changes in the genes of the hybrids. Hybrids have grown much larger than even the largest native tiger salamanders, enough so they can engulf smaller varieties of the natives and their larvae. Hybrids are delaying emerging from their larval stage for longer and longer periods. This means that if these salamanders where to completely outcompete their native counterparts and a bad drought were to occur, the salamanders would not be able to leave their larval stages fast enough to escape (Kanner, 2014).
