Gulf of California Xeric Scrub
This taxon occurs in the Gulf of California xeric scrub ecoregion, situated along the eastern coastal zone and Gulf of California versant of the Baja Peninsula in Mexico, and is delineated by the spine of the La Giganta Sierra Mountains. This ecoregion, located entirely within the nation of Mexico, is classified within the Deserts and Xeric Scrublands biome. Species richness of plants is high in the ecoregion, but modest for fauna; however, endemism is high in this arid habitat, which receives some of the lowest precipitation in all of Mexico.
Dominant flora species are Creosote Bush (Larrea tridentata) and White Bursage (Ambrosia dumosa); moreover, other plant taxa occurring here include: Arizona Nettle-spurge (Jatropha cinerea), Desert Ironwood (Olneya tesota), Acacia brandegeana, Blue Palo Verde (Cercidium floridum), and Chloroleucon mangense var. leucospermum. Species of more mesic habitats occur on the many oases that are present on the Baja Peninsula: Mexican Fan Palm (Washingtonia robusta), Southern Cattail (Typha domingensis), Common Reed (Phragmites australis) and Date Palm (Phoenix dactylifera). The oases are remnants of more extensive mesic environments that existed in the peninsula in prehistoric times; these earlier habitats consisted of larger bodies of surface water distributed throughout the peninsula, surrounded by vegetation that belongs to wetlands interspersed with common elements of the xeric scrub.
The Isla Santa Catalina Leaf-toed Gecko (Phyllodactylus bugastrolepis) is an endemic reptile to the Gulf of California xeric scrub, occurring only on Isla Santa Catalina, and often found in dead cacti. Other reptile species found here include: the endemic Santa Catalina Island Whiptail (Cnemidophorus catalinensis), seen only on Santa Catalina Island in the Gulf of California; the endemic Santa Catalina Island Spiny Lizard (Sceloporus lineatulus); the endemic San Lorenzo Islands Lizard (Uta antiqua); the endemic Salsipuedes Island Whiptail (Cnemidophorus canus), restricted in occurrence to endemic to the islands of Salsipuedes, San Lorenzo Norte and San Lorenzo Sur ; the endemic Raza Island Leaf-toed Gecko (Phyllodactylus tinklei), found on Raza Island; the endemic Santa Cruz Leaf-toed Gecko (Phyllodactylus santacruzensis); the endemic Isla Partida Del Norte Leaf-toed Gecko (Phyllodactylus partidus), found solely on Isla Partida Norte and Cardonosa Este, in the Gulf of California; the endemic Angel Island Leaf-toed Gecko (Phyllodactylus angelensis), found only on several Gulf of California islands in the county of Islas Angel de la Guarda; the endemic Las Animas Island Gecko (Phyllodactylus apricus); and the near-endemic Marbled Whiptail (Cnemidophorus marmoratus), the latter of which occupies burrows in sandy soils.
There are a number of mammalian taxa present in the Gulf of California xeric scrub, including: Angel Island Mouse (Peromyscus guardia CR), an ecoregion endemic known only from Ángel de la Guarda Island in the northern Gulf of California, México; the ecoregion endemic Burt's Deermouse (Peromyscus caniceps CR), known only from Montserrat Island, Baja California Sur, Mexico; Baja California Rock Squirrel (Spermophilus atricapillus EN), a Baja California endemic; and the Fish-eating Bat (Myotis vivesi VU), which is found along in the coastal zone of Baja California and Sonora. Bunker's Woodrat (Neotoma bunkeri EX) was previously endemic to the ecoregion and is now extinct.
Habitat and Ecology
IUCN Red List Assessment
Red List Category
Red List Criteria
Angel Island mouse
The Angel Island mouse or La Guarda deermouse (Peromyscus guardia) is a species of rodents in the family Cricetidae. It is endemic to Mexico, where it is historically known only from the island of Ángel de la Guarda, and nearby islets. The species is believed to be extirpated from the three smaller islands, and may be extinct on Ángel de la Guarda, as well. The species is threatened by predation by feral cats, and by competition from introduced rodents.
The Angel Island mouse has pale grey-brown fur with white underparts and feet, and large, hairless ears. It is most readily distinguished from closely related species on the mainland by subtle characteristics of the skull, or through genetic or biochemical analysis. Adults range from 19 to 22 cm (7.5 to 8.7 in) in total length, including tails 9 to 12 cm (3.5 to 4.7 in) long. Females have four abdominal teats.
Distribution and habitat
The Angel Island mouse is endemic to Ángel de la Guarda Island, a mountainous 359 sq mi (930 km2) island off the east coast of Baja California Sur, and to three much smaller islands in the same group. Within the islands, the species appears to be confined to sandy beaches, and perhaps to rockier areas nearby, and has not been found in the high mountainous terrain that forms most of their land area.
Three subspecies are formally recognised, although two of these are now extinct:
- P. g. guardia - Ángel de la Guarda, Estanque
- † P. g. harbisoni - Isla Granito
- † P. g. mejiae - Mejia
The Angel Island mouse is believed to be descended from an isolated population of cactus mice, possibly belonging to the P. e. fraterculus species or subspecies The critically endangered San Lorenzo mouse, which inhabits a smaller group of islands to the south, may be descended from the same stock, isolated when the islands separated from the mainland as sea levels rose at the end of the last Ice Age. The two species remain able to interbreed, although it is not known whether the resulting hybrids are fertile. Little is known of the behaviour or detailed biology of the species, although it is believed to breed in the spring.
As recently as the 1960s, the Angel Island mouse was reported to be abundant on at least three of the four islands it was known to inhabit. However, no specimens have been found on the islands since 1991, despite a number of surveys. The main risks to the species come from feral cats, and from introduced house mice and black rats, which compete with the endemic species for resources. The subspecies resident on the two northern islets are now listed as extinct, while the entire population on the southern islet of Estanque was probably driven to extinction by a single cat, present on the island only between 1998 and 1999.
The species is currently listed as critically endangered by the IUCN, but since no living specimens have been seen for 20 years, as of 2011, it may well be entirely extinct. If the species still survives, it is likely restricted to an area of no more than 10 km2 (3.9 sq mi).
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- Avise, J.C. et al. (1974). "Biochemical polymorphism and systematics in the genus Peromyscus: V. Insular and mainland species of the subgenus Haplomylomys". Systematic Zoology 23 (2): 226–238. doi:10.2307/2412134.
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- Álvarez-Castañeda, S.T. & Ortega-Rubio, A. (2003). "Current status of rodents on islands in the Gulf of California". Biological Conservation 109 (2): 157–163. doi:10.1016/S0006-3207(02)00121-0.
- Vázquez-Domínguez, E. et al. (2004). "Extirpation of an insular subspecies by a single introduced cat: the case of the endemic deer mouse, Peromyscus guardia on Estanque Island, Mexico". Oryx 38 (3): 347–350. doi:10.1017/S0030605304000602.
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