Land Snails
From Galapedia
| Land Snails in Galapagos | |
 Bulimulus sp. | |
| Size: | 6 to 25 millimeters in length. |
|---|---|
| Diet: | vegetation. |
| Status: | 26 species Critically Endangered, 22 species Endangered or Vulnerable |
The biodiversity of Land Snails (Bulimulus species) found in Galapagos continues to astound scientists studying the evolution of multiple species from a single ancestor. Yet the presence and activities of humans has impacted greatly on these invertebrates. Many are now considered endangered, prompting scientists working for the Charles Darwin Foundation (CDF) to preserve and restore these animals and their habitats.
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Unique to Galapagos
Fifty-seven endemic species of Land Snails are found in Galapagos. They are an excellent example of adaptive radiation - the rapid development of new species to fill many ecological habitats. Land snails are found throughout the major islands of Galapagos; however each species has a restricted range.
A greater diversity of species usually exists on higher islands with more different vegetation zones. For example, as many as 27 species have been found on Santa Cruz Island. These inhabit niches within the transitional zone through to the Scalesia forest.
Land snails eat vegetation. They vary in size from 6 to 25 millimeters in length. Color is also different between species, from white, dull or dark brown or black. They can only be active in humid conditions and many species hibernate during the cool dry season. This is achieved by anchoring themselves in a sheltered place using a seal of mucus or shelllike material.
Natural predators include ants, ground beetles, tiger beetles and mockingbirds.
Vulnerability
Based on results from a survey performed in 2001, the IUCN Red List indicates that:
- 26 species of Land Snail are Critically Endangered, and
- 22 species are Endangered or Vulnerable.
Many species were identified during the 19th century, many of which can now only be seen in museum collections from around the world.
Human activities have caused significant habitat destruction due to agricultural clearance as well as urbanization. Snails used to live in the Scalesia and transitional zones that have been heavily affected by farming. Road building and intentional or accidental fires have resulted in localized but dramatic effects, due to the limited range of some species. Bulimulus gilderoyi is restricted to a single valley in the highlands of Santa Cruz Island.
The introduction of exotic plants can also alter microclimates and microhabitats. Invertebrates that compete for habitat have also been introduced. These include the tiny pantropical snail (Subulina octona), black slug (Deroceras laeve), and the pest slug (Vaginulus plebeius). Introduced predators such as fire ants and black rats feed on the snails and destroy eggs, preventing reproduction. Finally, invasive animals such as goats, donkeys, pigs and cattle destroy vegetation and cause erosion; this has probably led to a number of losses of snail species.
Further losses can be expected with the increased severity of El Niño events linked to climate change. Loss of larger trees and the resulting open canopy will result in drier habitats at ground level. Whilst some snails will survive by hibernating in deep crevices, many will perish under these conditions.
CDRS research activities
Whilst little can be done to counteract climate change, other factors affecting the survival of Land Snails may be reduced. Strict adherence to quarantine regulations will hopefully prevent competitive or predatory species from being introduced.
CDF scientists and the Galapagos National Park Service (GNPS) are making excellent progress in dealing with invasive species. CDF botanists are tackling blackberry and red quinine, among other introduced plants. The successes of Project Isabela in eradicating goats, donkeys and pigs from northern Isabela and Santiago Islands will enable native vegetation to recover, and this will lead to the return of many invertebrate species. CDF invertebrate specialists will be closely monitoring this process.
Visiting scientists continue to work with the CDF to understand the genetic diversity of population structures for different species. Species with greater density and wider distribution are more likely to survive long term. Further studies to understand the role and demise of snails in Galapagos are needed. In the meantime, habitat protection and restoration will go a long way towards ensuring the survival of endemic Land Snails.
