Orthalicus reses
Encyclopedia
Orthalicus reses, common name
the Stock Island
treesnail, is a species
of large tropical air-breathing land snail
, a tree snail, a terrestrial
pulmonate gastropod mollusk in the family Orthalicidae
.
The nominate subspecies Orthalicus reses reses is threatened; it lives on trees in hardwood hammocks habitat in Southern Florida
, specifically the Florida Keys
.
. The genus Orthalicus occurs primarily in Central and South America. Two species occur in North America, Orthalicus reses and Orthalicus floridensis Pilsbry, both of which are restricted to South Florida. Orthalicus reses has two subspecies:
The Stock Island tree snail (Orthalicus reses) was first described by Thomas Say
in 1830, based on a snail which was probably collected in Key West
. That specimen was lost, and the species was later described by Henry Augustus Pilsbry
in 1946 using a snail collected from Stock Island
.
It is generally thought that the two subspecies of Orthalicus reses do not interbreed because of differences in their anatomy.
However, Emmel and Perry (2004) recommended that if the two Orthalicus reses subspecies prove to be as genetically invariant as was observed in their study, the groups should be considered a single taxon
or taxonomic unit. In that case, the nominate form, Orthalicus reses reses, would prevail and Orthalicus reses nesodryas would be demoted to a synonym
instead of a valid subspecies. Emmel and Perry (2004) asserted that the taxa “should continue to be considered as independent units for management purposes.”
that is approximately 45 to 55 mm in length. The external ground color of the shell is white to buff, with three poorly developed spiral bands and several flame-like purple-brown axial stripes that stop at the lower of the spiral bands. The thickness of the shell varies, but is usually more lightweight and translucent than other species of Orthalicus
. The axial stripes are typically narrower than their whitish interspaces, and do not fork near the upper suture. There are two to three white apical whorls
. The last whorl
contains two to four darker brown growth-rest varices
. The columella and parietal callus
are white or faint chestnut brown.
The nominate subspecies Orthalicus reses reses is distinguished from the supposed subspecies Orthalicus reses nesodryas by the lighter color pattern of the apical whorl, columella, and parietal callus. These characteristics are chestnut-brown or darker in Orthalicus reses nesodryas.
from Central America
and the Caribbean
shortly after the emergence of the Florida peninsula in the late Pleistocene
. Snails that were sealed to floating tropical trees may have been cast ashore on the Florida peninsula by high winds and hurricanes. This form of dispersal has been suggested for both Orthalicus and Liguus
, but the exact origin of these species is still in question. In 1972, Craig suggested that populations of Orthalicus arrived directly across the Gulf of Mexico
from Central America, but the mode of transportation and whether dispersal occurred on a single or multiple occasions was not known. No one knows when the Orthalicus reses reses arrived in the Lower Keys.
Historically, the Stock Island tree snail was believed to have a very limited distribution, being found only in tropical hardwood hammock
s on Stock Island and Key West
; although it may have been found in other hammock areas in the Lower Keys. Their distribution has since been artificially extended by collectors who have introduced them to Key Largo
and the southernmost parts of the mainland. Orthalicus reses nesodryas has a broader range, distributed throughout the Keys from Sugarloaf Key
north. Orthalicus floridensis is the only Orthalicus species to occur naturally on the mainland, and it is also found in the Keys.
This species is known to occur in the National Key Deer Refuge
.
and a tree trunk or branch. Snails secrete this mucus
seal that cements their shell to a tree in order to protect them from desiccation
during the dry period. Snails may come out of aestivation briefly to feed during dry-season rains, and also may go into aestivation during summer dry spells.
. Orthalicus reses survives best in hammocks with smooth-barked native trees that support relatively large amounts of lichen
s and algae
. In the Keys, Orthalicus is limited to the higher portions of the islands that support hammock forests (minimum elevations of 5 to 11 feet).
Lower Keys hammocks consist of thick forests of tropical trees and shrubs which grow in limestone
, marl
, and calcareous sand soils. Canopy trees include black ironwood (Krugiodendron ferreum
), gumbo limbo (Bursera simaruba
), Jamaican dogwood (Piscidia piscipula
), mahogany (Swietenia mahagoni
), pigeon plum (Coccoloba diversifolia), poisonwood (Metopium toxiferum
), and strangler fig (Ficus aurea
). Hammock understory contains torchwood (Amyris elemifera
), milkbark (Drypetes diversifolia), wild coffee (Psychotria nervosa
), marlberry (Ardisia escallonioides), stoppers (Eugenia
sp.), soldierwood (Colubrina elliptica
), crabwood (Gymnanthes lucida
), and velvetseed (Guettarda scabra).
Larger trees are more likely to support more Orthalicus reses reses snails than smaller trees, probably because they provide the snails with an increased surface area for foraging. It is not known if Orthalicus reses reses prefer certain tree types or species; however, Voss (1976) suggested tree snails generally prefer trees with smooth bark
over trees with rough bark, because it would require less energy to crawl over smooth bark. Voss also believed Orthalicus reses reses would prefer smooth bark because it would make it easier for them to form a secure mucous
seal when they were aestivating, resulting in lower mortalities from dehydration
or accidental dislodgement.
Orthalicus reses reses snails are entirely arboreal except when they move to the forest floor for nesting or traveling. Hammocks that contain well-developed soils or leaf litter are important for nesting activity and dispersal. Essential factors affecting food availability are the light intensity and moisture content of the hammock habitat.
No data are available on minimal hammock size needed to support a viable population of tree snails. Suitable habitat would have to include an area large enough to provide for foraging and nesting requirements, as well as provide for the microclimate
(air temperature and humidity) needed by the Orthalicus reses reses. Preferences for edge or interior hammock have been observed in Liguus
populations on Lignumvitae Key
. Age-class differences were seen where older individuals were found in the central mature hammock, while younger individuals were found more often along the edges of the hammock. Tuskes (1981) suggested this may be an adaptation
of younger snails to move to the edge to escape competition
from older snails. It is not known whether Orthalicus reses reses prefer interior or edge hammock areas. Recent surveys of snails in the Key Largo
populations have shown higher numbers of snails along the edge of the hammock than in the interior, but this result may be affected by the differences in visibility during surveying.
, and lichen
s found on many of the native hammock trees. Mixobacteria and some small mite
s may serve as a secondary food source. Feeding can occur at any time during the day or night with peak feeding activity occurring from late afternoon through the night to mid-morning and during or immediately after rainfall. When they are active, Orthalicus reses reses often follow a random twisting path that covers the entire bark surface, but they will move in a straight line if the surface moisture is abundant.
is common. Liguus
individuals are able to locate each other by following mucus trails, and Orthalicus reses reses likely do the same. They mate and nest in late summer and early fall during the wettest part of the rainy season. They lay approximately 15 eggs per clutch in a cavity that is dug into the soil humus layer, usually at the base of a tree, and take anywhere from 24 to 105 hours to deposit their eggs. The presence of this humus layer is essential for egg laying. The eggs hatch during the onset of the rains the following spring. Upon hatching the snails immediately proceed to climb adjacent trees. Most nesting snails appear to be approximately 2 to 3 years old and are estimated to live for up to 6 years, with 2.11 years being the mean age for the Stock Island population at the time of Deisler's study (1987). Tree snail age can be estimated by counting the number of dark "suture-like" lines resulting from pigment deposition during long dry spells (the dry season).
Orthalicus reses reses no longer occupies the Key West Botanical Forest and Garden
. In contrast, many populations exist on Key Largo
, well beyond Orthalicus reses reses historic range, as a result of relocations by snail collectors. The majority of relocations occurred by the late 1990s. These were largely carried out by private hobbyists who sought to thwart extinction. However, these actions were poorly documented and subsequently poorly monitored. One clear trend is that Key Largo has accumulated more populations than the Lower Keys.
, since 2 August 1978. It was originally listed as Orthalicus reses. However, Othalicus reses comprises two recognized taxa, and only Orthalicus reses reses is threatened. In the time of listing, the Florida Game and Fresh Water Fish Commission favored listing, since intensive development has reduced the range to Stock Island
. Leslie Hubricht
and Alan Solem
supported listing. Solem believed that collecting or expansion of tourist facilities could have drastic effects. The primary threat to Orthalicus reses reses at the time of listing was habitat loss due to development. Additional threats include pesticides, hurricanes, vegetation trimming along utility corridors, overutilization, and non-native predators. Trends in those threats are continuing at the same level, except for predation, the threat level for which is unknown. The population trend is unknown in 2009.
The recovery criteria largely pertain to habitat, in particular a minimum number of sites (four) and habitat stability for those sites in the Lower Keys. However, only one Lower Keys site is currently occupied by a persistent population, whereas more populations and larger numbers of Orthalicus reses reses occur at various sites in the Upper Keys. In the Lower Keys, the No Name Key
population is the only one that
persists in natural surroundings and generally appears to be viable. Accordingly, the criteria do not reflect the best available and most up-to-date information on the biology of the species because they treat the Lower Keys as the only area to conduct reintroductions and otherwise achieve recovery for Orthalicus reses reses. Moreover, significant threats in addition to habitat loss have emerged, and these are not adequately addressed in the recovery criteria.
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
the Stock Island
Stock Island, Florida
Stock Island is a census-designated place on an island of the same name in Monroe County, Florida, United States. The population of the CDP was 4,410 at the 2000 census. It is located on the portion of the island south of US-1. It is supposedly named for the herds of livestock formerly kept there...
treesnail, is a species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of large tropical air-breathing land snail
Snail
Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...
, a tree snail, a terrestrial
Terrestrial animal
Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...
pulmonate gastropod mollusk in the family Orthalicidae
Orthalicidae
Orthalicidae are a family of tropical air-breathing land snails, terrestrial pulmonate gastropod mollusks are classified in the informal group Sigmurethra of the clade Stylommatophora...
.
The nominate subspecies Orthalicus reses reses is threatened; it lives on trees in hardwood hammocks habitat in Southern Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
, specifically the Florida Keys
Florida Keys
The Florida Keys are a coral archipelago in southeast United States. They begin at the southeastern tip of the Florida peninsula, about south of Miami, and extend in a gentle arc south-southwest and then westward to Key West, the westernmost of the inhabited islands, and on to the uninhabited Dry...
.
Taxonomy
Orthalicus reses is a species within the genus Orthalicus, a group of large, arboreal pulmonate snails in the family OrthalicidaeOrthalicidae
Orthalicidae are a family of tropical air-breathing land snails, terrestrial pulmonate gastropod mollusks are classified in the informal group Sigmurethra of the clade Stylommatophora...
. The genus Orthalicus occurs primarily in Central and South America. Two species occur in North America, Orthalicus reses and Orthalicus floridensis Pilsbry, both of which are restricted to South Florida. Orthalicus reses has two subspecies:
- Orthalicus reses reses (SayThomas SayThomas Say was an American naturalist, entomologist, malacologist, herpetologist and carcinologist. A taxonomist, he is often considered to be the father of descriptive entomology in the United States. He described more than 1,000 new species of beetles and over 400 species of insects of other...
, 1830) - Stock Island tree snail - Orthalicus reses nesodryas PilsbryHenry Augustus PilsbryHenry Augustus Pilsbry was an American biologist, malacologist and carcinologist, among other areas of study. He was a dominant presence in many fields of invertebrate taxonomy for the better part of a century...
, 1946 - Florida Keys treesnail
The Stock Island tree snail (Orthalicus reses) was first described by Thomas Say
Thomas Say
Thomas Say was an American naturalist, entomologist, malacologist, herpetologist and carcinologist. A taxonomist, he is often considered to be the father of descriptive entomology in the United States. He described more than 1,000 new species of beetles and over 400 species of insects of other...
in 1830, based on a snail which was probably collected in Key West
Key West
Key West is an island in the Straits of Florida on the North American continent at the southernmost tip of the Florida Keys. Key West is home to the southernmost point in the Continental United States; the island is about from Cuba....
. That specimen was lost, and the species was later described by Henry Augustus Pilsbry
Henry Augustus Pilsbry
Henry Augustus Pilsbry was an American biologist, malacologist and carcinologist, among other areas of study. He was a dominant presence in many fields of invertebrate taxonomy for the better part of a century...
in 1946 using a snail collected from Stock Island
Stock Island
Stock Island is an island in the lower Florida Keys immediately east of Key West . Immediately northwest is Key Haven , from which it is connected by causeway with US 1 . The part north of U.S...
.
It is generally thought that the two subspecies of Orthalicus reses do not interbreed because of differences in their anatomy.
However, Emmel and Perry (2004) recommended that if the two Orthalicus reses subspecies prove to be as genetically invariant as was observed in their study, the groups should be considered a single taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
or taxonomic unit. In that case, the nominate form, Orthalicus reses reses, would prevail and Orthalicus reses nesodryas would be demoted to a synonym
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
instead of a valid subspecies. Emmel and Perry (2004) asserted that the taxa “should continue to be considered as independent units for management purposes.”
Description
Orthalicus reses is a snail with a large, conical shellGastropod shell
The gastropod shell is a shell which is part of the body of a gastropod or snail, one kind of mollusc. The gastropod shell is an external skeleton or exoskeleton, which serves not only for muscle attachment, but also for protection from predators and from mechanical damage...
that is approximately 45 to 55 mm in length. The external ground color of the shell is white to buff, with three poorly developed spiral bands and several flame-like purple-brown axial stripes that stop at the lower of the spiral bands. The thickness of the shell varies, but is usually more lightweight and translucent than other species of Orthalicus
Orthalicus
Orthalicus is a genus of air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Orthalicidae.- Species :Species within the genus Orthalicus include:* Orthalicus floridensis - banded treesnail * Orthalicus undatus...
. The axial stripes are typically narrower than their whitish interspaces, and do not fork near the upper suture. There are two to three white apical whorls
Whorl (mollusc)
A whorl is a single, complete 360° revolution or turn in the spiral growth of a mollusc shell. A spiral configuration of the shell is found in of numerous gastropods, but it is also found in shelled cephalopods including Nautilus, Spirula and the large extinct subclass of cephalopods known as the...
. The last whorl
Body whorl
Body whorl is part of the morphology of a coiled gastropod mollusk.- In gastropods :In gastropods, the body whorl, or last whorl, is the most recently-formed and largest whorl of a spiral or helical shell, terminating in the aperture...
contains two to four darker brown growth-rest varices
Varix (mollusc)
A varix is an anatomical feature of the shell of certain sea snails, marine gastropod molluscs.It is a thickened axial ridge in the shell of some families of gastropods. A varix is located at intervals around the whorl, and is formed by considerable thickening of the outer lip at a resting stage...
. The columella and parietal callus
Parietal callus
A parietal callus is a feature of the shell anatomy of some groups of snails, i.e. gastropods. It is a thickened calcareous deposit which may be present on the parietal wall of the aperture of the adult shell. The parietal wall is the margin of the aperture and part of the wall of the body whorl...
are white or faint chestnut brown.
The nominate subspecies Orthalicus reses reses is distinguished from the supposed subspecies Orthalicus reses nesodryas by the lighter color pattern of the apical whorl, columella, and parietal callus. These characteristics are chestnut-brown or darker in Orthalicus reses nesodryas.
Distribution
Henry Augustus Pilsbry suggested in 1946, that Orthalicus reses reses arrived in FloridaFlorida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
from Central America
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
and the Caribbean
Caribbean
The Caribbean is a crescent-shaped group of islands more than 2,000 miles long separating the Gulf of Mexico and the Caribbean Sea, to the west and south, from the Atlantic Ocean, to the east and north...
shortly after the emergence of the Florida peninsula in the late Pleistocene
Late Pleistocene
The Late Pleistocene is a stage of the Pleistocene Epoch. The beginning of the stage is defined by the base of the Eemian interglacial phase before the final glacial episode of the Pleistocene 126,000 ± 5,000 years ago. The end of the stage is defined exactly at 10,000 Carbon-14 years BP...
. Snails that were sealed to floating tropical trees may have been cast ashore on the Florida peninsula by high winds and hurricanes. This form of dispersal has been suggested for both Orthalicus and Liguus
Liguus
Liguus is a genus of large tropical air-breathing land snails, more specifically arboreal or tree snails, terrestrial pulmonate gastropod mollusks in the family Orthalicidae....
, but the exact origin of these species is still in question. In 1972, Craig suggested that populations of Orthalicus arrived directly across the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
from Central America, but the mode of transportation and whether dispersal occurred on a single or multiple occasions was not known. No one knows when the Orthalicus reses reses arrived in the Lower Keys.
Historically, the Stock Island tree snail was believed to have a very limited distribution, being found only in tropical hardwood hammock
Tropical hardwood hammock
Tropical hardwood hammocks are closed canopy forests, dominated by a diverse assemblage of evergreen and semi-deciduous tree and shrub species, mostly of West Indian origin...
s on Stock Island and Key West
Key West
Key West is an island in the Straits of Florida on the North American continent at the southernmost tip of the Florida Keys. Key West is home to the southernmost point in the Continental United States; the island is about from Cuba....
; although it may have been found in other hammock areas in the Lower Keys. Their distribution has since been artificially extended by collectors who have introduced them to Key Largo
Key Largo
Key Largo is an island in the upper Florida Keys archipelago and, at long, the largest of the Keys. It is also the northernmost of the Florida Keys in Monroe County, and the northernmost of the Keys connected by U.S. Highway 1...
and the southernmost parts of the mainland. Orthalicus reses nesodryas has a broader range, distributed throughout the Keys from Sugarloaf Key
Sugarloaf Key
Sugarloaf Key is a single island in the lower Florida Keys that forms a loop on the Atlantic Ocean side giving the illusion of separate islands. Although frequently referred to simply and with technical accuracy as "Sugarloaf Key", this island contains two distinct island communities, known as...
north. Orthalicus floridensis is the only Orthalicus species to occur naturally on the mainland, and it is also found in the Keys.
This species is known to occur in the National Key Deer Refuge
National Key Deer Refuge
The National Key Deer Refuge is a National Wildlife Refuge located on Big Pine Key and No Name Key in the Florida Keys in Monroe County, Florida....
.
Behavior
Orthalicus reses reses snails are active mainly during the wet season, May through November, during which time breeding, feeding, and dispersal takes place. Dry periods (December through April) are spent in aestivation, during which time the snail forms a tight sealed barrier between the apertureAperture (mollusc)
The aperture is an opening in certain kinds of mollusc shells: it is the main opening of the shell, where part of the body of the animal emerges for locomotion, feeding, etc....
and a tree trunk or branch. Snails secrete this mucus
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
seal that cements their shell to a tree in order to protect them from desiccation
Desiccation
Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately sealed container.-Science:...
during the dry period. Snails may come out of aestivation briefly to feed during dry-season rains, and also may go into aestivation during summer dry spells.
Habitat
Originally, Orthalicus reses occurred exclusively in hardwood hammocks of the KeysFlorida Keys
The Florida Keys are a coral archipelago in southeast United States. They begin at the southeastern tip of the Florida peninsula, about south of Miami, and extend in a gentle arc south-southwest and then westward to Key West, the westernmost of the inhabited islands, and on to the uninhabited Dry...
. Orthalicus reses survives best in hammocks with smooth-barked native trees that support relatively large amounts of lichen
Lichen
Lichens are composite organisms consisting of a symbiotic organism composed of a fungus with a photosynthetic partner , usually either a green alga or cyanobacterium...
s and algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
. In the Keys, Orthalicus is limited to the higher portions of the islands that support hammock forests (minimum elevations of 5 to 11 feet).
Lower Keys hammocks consist of thick forests of tropical trees and shrubs which grow in limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
, marl
Marl
Marl or marlstone is a calcium carbonate or lime-rich mud or mudstone which contains variable amounts of clays and aragonite. Marl was originally an old term loosely applied to a variety of materials, most of which occur as loose, earthy deposits consisting chiefly of an intimate mixture of clay...
, and calcareous sand soils. Canopy trees include black ironwood (Krugiodendron ferreum
Krugiodendron ferreum
Krugiodendron ferreum, commonly known as the Black Ironwood or Leadwood, is a species of tree in the buckthorn family, Rhamnaceae. It is found in southern Florida, throughout the Caribbean and from southern Mexico to Honduras...
), gumbo limbo (Bursera simaruba
Bursera simaruba
Bursera simaruba, commonly known as the Gumbo-limbo, is a tree species in the family Burseraceae, native to tropical regions of the Americas from the southeasternmost United States south through Mexico and the Caribbean to Brazil and Venezuela...
), Jamaican dogwood (Piscidia piscipula
Piscidia piscipula
Piscidia piscipula, commonly named Florida fishpoison tree, Jamaican dogwood or Fishfuddle, is a medium-sized, deciduous, tropical tree endemic to southern Florida, the Florida Keys, Texas, Caribbean, and Latin America. Native Americans of the West Indies discovered extracts from the tree could...
), mahogany (Swietenia mahagoni
Swietenia mahagoni
Swietenia mahagoni, commonly known as the West Indies Mahogany, is a species of Swietenia native to southern Florida, USA, The Bahamas, Cuba, Jamaica, and Hispaniola. It is the species from which the original mahogany wood was produced....
), pigeon plum (Coccoloba diversifolia), poisonwood (Metopium toxiferum
Metopium toxiferum
Metopium toxiferum is a species of flowering tree in the cashew or sumac family, Anacardiaceae, that is native to the American neotropics...
), and strangler fig (Ficus aurea
Ficus aurea
Ficus aurea, commonly known as the Florida strangler fig , golden fig, or higuerón, is a tree in the family Moraceae that is native to the U.S. state of Florida, the northern and western Caribbean, southern Mexico and Central America south to Panama...
). Hammock understory contains torchwood (Amyris elemifera
Amyris elemifera
Amyris elemifera, commonly known as Sea Torchwood, is a coastal evergreen shrub or small tree. It is found in central and southern Florida in the United States, The Bahamas, the Caribbean, and the Central American countries of Guatemala, Belize, Honduras, and El Salvador. The resinous wood has been...
), milkbark (Drypetes diversifolia), wild coffee (Psychotria nervosa
Psychotria nervosa
Psychotria nervosa, also known as wild coffee, is a shade tolerant medium-sized shrub native to Florida as well as Central and South America. It produces "small, red, ellipsoid fruit" that resemble "the true coffee bean" in shape and attract birds...
), marlberry (Ardisia escallonioides), stoppers (Eugenia
Eugenia
Eugenia is a genus of flowering plants in the myrtle family Myrtaceae. It has a worldwide, although highly uneven, distribution in tropical and subtropical regions. The bulk of the approximately 1,000 species occur in the New World tropics, especially in the northern Andes, the Caribbean, and the...
sp.), soldierwood (Colubrina elliptica
Colubrina elliptica
Colubrina elliptica, Mabi or Soldierwood, is a species of flowering tree in the buckthorn family, Rhamnaceae, that is native to the Florida Keys, the Caribbean, Central America, Mexico, and Venezuela.-Uses:...
), crabwood (Gymnanthes lucida
Gymnanthes lucida
Gymnanthes lucida, commonly known as Shiny Oysterwood, is a species of flowering plant in the spurge family, Euphorbiaceae, that is native to southern Florida in the United States, the Bahamas, the Caribbean, Mexico, and Central America. It is a tree, reaching a height of ....
), and velvetseed (Guettarda scabra).
Larger trees are more likely to support more Orthalicus reses reses snails than smaller trees, probably because they provide the snails with an increased surface area for foraging. It is not known if Orthalicus reses reses prefer certain tree types or species; however, Voss (1976) suggested tree snails generally prefer trees with smooth bark
Bark
Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines and shrubs. Bark refers to all the tissues outside of the vascular cambium and is a nontechnical term. It overlays the wood and consists of the inner bark and the outer bark. The inner...
over trees with rough bark, because it would require less energy to crawl over smooth bark. Voss also believed Orthalicus reses reses would prefer smooth bark because it would make it easier for them to form a secure mucous
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
seal when they were aestivating, resulting in lower mortalities from dehydration
Dehydration
In physiology and medicine, dehydration is defined as the excessive loss of body fluid. It is literally the removal of water from an object; however, in physiological terms, it entails a deficiency of fluid within an organism...
or accidental dislodgement.
Orthalicus reses reses snails are entirely arboreal except when they move to the forest floor for nesting or traveling. Hammocks that contain well-developed soils or leaf litter are important for nesting activity and dispersal. Essential factors affecting food availability are the light intensity and moisture content of the hammock habitat.
No data are available on minimal hammock size needed to support a viable population of tree snails. Suitable habitat would have to include an area large enough to provide for foraging and nesting requirements, as well as provide for the microclimate
Microclimate
A microclimate is a local atmospheric zone where the climate differs from the surrounding area. The term may refer to areas as small as a few square feet or as large as many square miles...
(air temperature and humidity) needed by the Orthalicus reses reses. Preferences for edge or interior hammock have been observed in Liguus
Liguus
Liguus is a genus of large tropical air-breathing land snails, more specifically arboreal or tree snails, terrestrial pulmonate gastropod mollusks in the family Orthalicidae....
populations on Lignumvitae Key
Lignumvitae Key
Lignumvitae Key is an island in the upper Florida Keys.It is located due north of, and less than one mile from the easternmost tip of Lower Matecumbe Key....
. Age-class differences were seen where older individuals were found in the central mature hammock, while younger individuals were found more often along the edges of the hammock. Tuskes (1981) suggested this may be an adaptation
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
of younger snails to move to the edge to escape competition
Competition
Competition is a contest between individuals, groups, animals, etc. for territory, a niche, or a location of resources. It arises whenever two and only two strive for a goal which cannot be shared. Competition occurs naturally between living organisms which co-exist in the same environment. For...
from older snails. It is not known whether Orthalicus reses reses prefer interior or edge hammock areas. Recent surveys of snails in the Key Largo
Key Largo
Key Largo is an island in the upper Florida Keys archipelago and, at long, the largest of the Keys. It is also the northernmost of the Florida Keys in Monroe County, and the northernmost of the Keys connected by U.S. Highway 1...
populations have shown higher numbers of snails along the edge of the hammock than in the interior, but this result may be affected by the differences in visibility during surveying.
Feeding habits
The rate at which individuals of Orthalicus reses reses grow is dependent upon the availability of food, and how quickly their food is replenished after being grazed. Food regrowth is affected by the light intensity and moisture (canopy density and climate) of the hammock habitat. They feed on epiphytic growth on hardwood tree trunks, branches, and leaves. Little is known about the feeding habits or food preferences of the Orthalicus reses reses. Likely food items include a variety of fungi, algaeAlgae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
, and lichen
Lichen
Lichens are composite organisms consisting of a symbiotic organism composed of a fungus with a photosynthetic partner , usually either a green alga or cyanobacterium...
s found on many of the native hammock trees. Mixobacteria and some small mite
Mite
Mites, along with ticks, are small arthropods belonging to the subclass Acari and the class Arachnida. The scientific discipline devoted to the study of ticks and mites is called acarology.-Diversity and systematics:...
s may serve as a secondary food source. Feeding can occur at any time during the day or night with peak feeding activity occurring from late afternoon through the night to mid-morning and during or immediately after rainfall. When they are active, Orthalicus reses reses often follow a random twisting path that covers the entire bark surface, but they will move in a straight line if the surface moisture is abundant.
Life cycle
Orthalicus reses reses snails are hermaphroditic, and cross-fertilizationCross-fertilization
Cross-fertilization can refer to:*Allogamy, where an ovum from one individual is fertilized with the spermatozoa of another*Heterosis, where different strains are cross-bred to form a hybrid...
is common. Liguus
Liguus
Liguus is a genus of large tropical air-breathing land snails, more specifically arboreal or tree snails, terrestrial pulmonate gastropod mollusks in the family Orthalicidae....
individuals are able to locate each other by following mucus trails, and Orthalicus reses reses likely do the same. They mate and nest in late summer and early fall during the wettest part of the rainy season. They lay approximately 15 eggs per clutch in a cavity that is dug into the soil humus layer, usually at the base of a tree, and take anywhere from 24 to 105 hours to deposit their eggs. The presence of this humus layer is essential for egg laying. The eggs hatch during the onset of the rains the following spring. Upon hatching the snails immediately proceed to climb adjacent trees. Most nesting snails appear to be approximately 2 to 3 years old and are estimated to live for up to 6 years, with 2.11 years being the mean age for the Stock Island population at the time of Deisler's study (1987). Tree snail age can be estimated by counting the number of dark "suture-like" lines resulting from pigment deposition during long dry spells (the dry season).
Interaction with other snails in the genus
Emmel and Perry (2004) believed there to be shifts in the relative abundances of the three Orthalicus taxa in the Keys. In the past, the Orthalicus floridensis was the most common and widespread of the three, whereas subsequent to 2000, Emmel and Perry (2004) considered the Orthalicus floridensis to be the rarest. This situation results partly from the translocations that bolstered Orthalicus reses reses distribution and allowed them to avoid extinction, but probably also reflects actual declines in Orthalicus floridensis populations over time. Orthalicus reses reses now occur in sympatry with their congeners in several locations. The observations of Emmel and Perry (2004) suggested that translocated Orthalicus reses reses, all of which are outside the historic range, perform as well or better than congeners in those places where they overlap.Population biology
The abundance and range of Orthalicus reses reses declined throughout the 20th century. Rigorous estimates of Orthalicus reses reses numbers are not known for any population. Orthalicus reses reses status is currently assessed by the numbers of discrete populations that are known. Accordingly, potential trend information only includes observations of whether various populations continue to persist. However, for most populations, even the area occupied is poorly defined. As of 2006, a tabulation of all well-known and poorly documented sites indicated that Orthalicus reses reses occupied approximately 25 sites in the Florida Keys (Monroe County) and two sites on the mainland (Miami-Dade County). However, for many of those sites, even confirmation as to whether Orthalicus reses reses persists in recent years is lacking. Survey and monitoring efforts have been limited and highly variable, and methodologies are usually not reported in detail. Whereas Orthalicus reses reses occupies more sites at present than in the recorded past, the total area occupied remains unknown, as are trends in abundance and demographics. Overall, however, the Orthalicus reses reses population status appears to be more secure than when it was listed, due to the widespread translocations that occurred subsequently.Orthalicus reses reses no longer occupies the Key West Botanical Forest and Garden
Key West Botanical Forest and Garden
The Key West Tropical Forest & Botanical Garden 11 acres is a frost-free arboretum and botanical garden containing a fine collection of trees, shrubs, and palms, including several "champion tree" specimens. It is located at 5210 College Road, Key West, Florida, USA...
. In contrast, many populations exist on Key Largo
Key Largo
Key Largo is an island in the upper Florida Keys archipelago and, at long, the largest of the Keys. It is also the northernmost of the Florida Keys in Monroe County, and the northernmost of the Keys connected by U.S. Highway 1...
, well beyond Orthalicus reses reses historic range, as a result of relocations by snail collectors. The majority of relocations occurred by the late 1990s. These were largely carried out by private hobbyists who sought to thwart extinction. However, these actions were poorly documented and subsequently poorly monitored. One clear trend is that Key Largo has accumulated more populations than the Lower Keys.
Conservation
Orthalicus reses reses is listed as threatened on the United States Fish and Wildlife Service list of endangered speciesUnited States Fish and Wildlife Service list of endangered species
This list contains only the bird and mammal species described as endangered by the United States Fish and Wildlife Service. It contains species not only in the U.S. and its territories, but also species only found abroad. It does not contain fish, amphibians, reptiles, plants, or invertebrates,...
, since 2 August 1978. It was originally listed as Orthalicus reses. However, Othalicus reses comprises two recognized taxa, and only Orthalicus reses reses is threatened. In the time of listing, the Florida Game and Fresh Water Fish Commission favored listing, since intensive development has reduced the range to Stock Island
Stock Island, Florida
Stock Island is a census-designated place on an island of the same name in Monroe County, Florida, United States. The population of the CDP was 4,410 at the 2000 census. It is located on the portion of the island south of US-1. It is supposedly named for the herds of livestock formerly kept there...
. Leslie Hubricht
Leslie Hubricht
Leslie Hubricht was an American biologist and malacologist.If he had lived in a previous century, Hubricht would have been called a "gentleman naturalist"...
and Alan Solem
Alan Solem
Alan Solem, full name George Alan Solem was an American malacologist, a biologist who studied mollusks.He was one of the most renown land snail experts of his time and had earned a reputation for his comprehensive revisions of mainly terrestrial pulmonates...
supported listing. Solem believed that collecting or expansion of tourist facilities could have drastic effects. The primary threat to Orthalicus reses reses at the time of listing was habitat loss due to development. Additional threats include pesticides, hurricanes, vegetation trimming along utility corridors, overutilization, and non-native predators. Trends in those threats are continuing at the same level, except for predation, the threat level for which is unknown. The population trend is unknown in 2009.
The recovery criteria largely pertain to habitat, in particular a minimum number of sites (four) and habitat stability for those sites in the Lower Keys. However, only one Lower Keys site is currently occupied by a persistent population, whereas more populations and larger numbers of Orthalicus reses reses occur at various sites in the Upper Keys. In the Lower Keys, the No Name Key
No Name Key
No Name Key is an island located in the lower Florida Keys in the United States. It is 3 miles from US 1 and sparsely populated with only 43 homes. It is a fairly small island in comparison to its neighbor, Big Pine Key, which lies about a half mile to its west...
population is the only one that
persists in natural surroundings and generally appears to be viable. Accordingly, the criteria do not reflect the best available and most up-to-date information on the biology of the species because they treat the Lower Keys as the only area to conduct reintroductions and otherwise achieve recovery for Orthalicus reses reses. Moreover, significant threats in addition to habitat loss have emerged, and these are not adequately addressed in the recovery criteria.
Further reading
- Forys, E.A., A. Quistorff, C. R. Allen, and D.P. Wojcik. (2001). "The likely cause of extinction of the tree snail Orthalicus reses reses (Say)". Journal of Molluscan Studies 67: 369-376. abstract
- (2001) STOCK ISLAND TREE SNAIL Orthalicus reses reses. In: Field Guide to the Rare Animals of Florida. Florida Natural Areas Inventory.
- Tryon G. W.George Washington TryonGeorge Washington Tryon, Jr. was an American malacologist who worked at the Academy of Natural Sciences in Philadelphia.- Biography :George Washington Tryon was the son of Edward K. Tryon and Adeline Savidt...
(1899) Manual of Conchology, structural and systematic, with illustrations of the species. Second series: Pulmonata. Volume 12. American Bulimulidae: North American and Antillean Drymaeus, Leiostracus, Orthalicinae and Amphibuliminae. 109-110. Plate 27, figure 24-26.
External links
- Species Profile of Stock Island Tree snail (Orthalicus reses) at U.S. Fish & Wildlife Service webpage
- Photo of shell of Orthalicus reses reses
- Photo of shell of Orthalicus reses nesodryas
- at NatureServe Explorer:
- http://www.natureserve.org/explorer/servlet/NatureServe?sourceTemplate=tabular_report.wmt&loadTemplate=species_RptComprehensive.wmt&selectedReport=RptComprehensive.wmt&summaryView=tabular_report.wmt&elKey=117235&paging=home&save=true&startIndex=1&nextStartIndex=1&reset=false&offPageSelectedElKey=116348&offPageSelectedElType=species&offPageYesNo=true&post_processes=&radiobutton=radiobutton&selectedIndexes=116348&selectedIndexes=117235&selectedIndexes=119125&selectedIndexes=119076Orthalicus reses]
- http://www.natureserve.org/explorer/servlet/NatureServe?sourceTemplate=tabular_report.wmt&loadTemplate=species_RptComprehensive.wmt&selectedReport=RptComprehensive.wmt&summaryView=tabular_report.wmt&elKey=119076&paging=home&save=true&startIndex=1&nextStartIndex=1&reset=false&offPageSelectedElKey=116348&offPageSelectedElType=species&offPageYesNo=true&post_processes=&radiobutton=radiobutton&selectedIndexes=116348&selectedIndexes=117235&selectedIndexes=119125&selectedIndexes=119076Orthalicus reses reses]
- http://www.natureserve.org/explorer/servlet/NatureServe?sourceTemplate=tabular_report.wmt&loadTemplate=species_RptComprehensive.wmt&selectedReport=RptComprehensive.wmt&summaryView=tabular_report.wmt&elKey=119125&paging=home&save=true&startIndex=1&nextStartIndex=1&reset=false&offPageSelectedElKey=116348&offPageSelectedElType=species&offPageYesNo=true&post_processes=&radiobutton=radiobutton&selectedIndexes=116348&selectedIndexes=117235&selectedIndexes=119125&selectedIndexes=119076Orthalicus reses nesodryas]