Clearly, the most important factor leading to amphibian population declines is habitat destruction. When forests are cleared it is no surprise that species that once lived there disappear. What is alarming is that there are many cases where the habitat is protected and amphibians are still disappearing. The causes for recent amphibian declines are many, but an emerging disease called chytridiomycosis and global climate change are thought the be the biggest threats to amphibians. Chytridiomycosis is a disease caused by the fungal chytrid pathogen Batrachochytrium dendrobatidis. This pathogen is associated with the global loss of hundreds of species of amphibians and represents a spectacular loss of biodiversity, some say the worst in recorded history.
In the table below we break down all of the hypothesized factors and the links provide more detailed information for each one. Some factors are obviously shared with other types of endangered species on our planet and are part of to the worldwide biodiversity crisis such as habitat destruction, alteration and fragmentation (Fisher and Shaffer 1996, Davidson et al. 2001, Marsh and Trenham 2001), introduced species (Vredenburg 2004, Kats and Ferrer 2003) and over-exploitation (Jennings and Hayes 1985, Lannoo et al. 1994). For these threats, we have a pretty good understanding of the ecological mechanisms underlying declines (Collins and Storfer 2003). However, amphibians have also declined in relatively ‘pristine’ and protected environments (Wake 1991, Crump et al. 1992, Lips 2000). These more complex and elusive mechanisms include climate change (Pounds et al. 1999, Kiesecker et al. 2001, Carey and Alexander 2003), increased UV-B radiation, chemical contaminants (Hayes et al. 2002, Blaustein et al. 2003), emerging infectious diseases (Daszak et al. 2003; see AmphibiaWeb's global distribution map of chytrid) and deformities (or malformations). The underlying mechanisms behind these factors are complex and they may be working synergistically with more straight forward factors, such as habitat destruction and introduced species, to exacerbate declines (Kiesecker et al. 2001, Blaustein and Kiesecker 2002). Researchers are finding that there is not a single overarching cause for global declines, instead all of these factors are threatening amphibian populations and the threat tends to vary depending on the location. If we are going to prevent further extinctions, research must move forward quickly and be used effectively in management by governments and non-governmental organizations around the world.
