Geology topics
Publications and source records attributed to G. B. Rathbun.
The future looks bleak for the manatee population in the waters around Haiti. Results of a survey conducted by the US Fish and Wildlife Service suggest that numbers have declined drastically over the last 50 years. The best hope for the few remaining is that the hunting expertise will vanish with the older generation.
Hemograms on blood obtained from 10 clinically normal West Indian Manatees ( Trichechus manatus ) were studied. The red cells were large and in lower number than in most terrestrial species. The manatee does not have a neutrophil as is present in most species, but it has a heterophil whose granules stain pink with the Wright-Giemsa stain. The eosinophil has uniform red-staining granules that make its differentiation from heterophils difficult. Both large and small lymphocytes, monocytes and basophils are present. The total number of white blood cells was comparable to that of common domestic species as were the platelet numbers. No reticulocytes were found.
The recommendations and implementation of the IUCN conservation plan for African Insectivora and elephant-shrews (Nicoll & Rathbun, 1990) are reviewed. Of the 33 species and subspecies of elephant-shrews, only six forest-dwelling taxa are threatened. Until additional status data are gathered, assessed, and published no changes in the IUCN threatened categories should be made: Rhynchocyon chrysopygus is ‘vulnerable’; Rhynchocyon petersi petersi and Rhynchocyon petersi adersi are ‘rare’; and Rhynchocyon cirnei cirnei, Rhynchocyon cirnei hendersoni , and Petrodromus tetradactylus sangi are ‘insufficiently known’. Implementing status surveys that have not been completed, especially for the forms of R. petersi and P. t. sangi , are a high priority. Rhynchocyon petersi and R. chrysopygus densities are lower in altered and trapped forests compared with undisturbed forests. Because undisturbed forests in eastern Africa are highly fragmented, small, and disappearing due to human encroachment, it is important to determine the population dynamics of Rhynchocyon spp. that occupy degraded forest habitats, such as plantations, follow agricultural lands, and coastal scrub. In the face of the expanding human population, with its increasing need for land and natural resources, Rhynchocyon populations that occur in these degraded habitats may be all that remain in the future.
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Over a 10-wk period in early 1982, 39 Florida manatees ( Trichechus manatus latirostris ) were found dead in the lower Caloosahatchee River and nearby waters of southwestern Florida. Two were killed by boats. The remainder showed no evidence of trauma. Lesions indicative of infectious agents were not identified, and bacteriological and contaminant residue findings were unremarkable. Nonspecific lesions of congestion and hemorrhage were identified in brain tissue. Numerous reports were also received of manatee morbidity. Some distressed manatees showed no biochemical lesions in clinical analyses of blood samples and recovered quickly. Timing of manatee illnesses coincided with fish and double-crested cormorant ( Phalacrocorax auritus ) mortality and morbidity. A widespread bloom of the dinoflagellate red tide organism ( Gymnodinium breve ) also coincided with these incidents. G. breve produces potent neurotoxins (brevetoxins). Circumstantial evidence links these events, and possible routes of exposure may include ingestion of filter-feeding ascidians. Ecological conditions that magnified the extent of the epizootic included an early dispersal of manatees into the area from a nearby winter aggregation site and unusually high salinities that facilitated the inshore spread of the red tide bloom. Management responses to future episodes of red tide in manatee areas are suggested.
Photographs of distinctively scarred manatees ( Trichechus manatus ) were taken at aggregation sites throughout Florida and assembled into a catalog for identifying individuals. Resightings of known manatees in different years or at different locations enabled us to document site fidelity and long-distance movements. Of the 891 individuals included in the catalog as of August 1986, 470 (53%) were resighted at least once. We documented 219 cases of seasonal returns to specific aggregation sites and 98 instances of movements between areas. Movements in excess of 820 km were documented for individuals on the east coast of Florida. Rapid movements south during early winter, as well as northerly spring movements, verify a seasonal migration pattern for many individuals along Florida's east coast. The wide-ranging migratory habits of manatees in Florida must be considered if meaningful management strategies are to be developed and implemented.
We recognize three levels of extinction–global, local, and ecological – and provide examples of each. The protection and recovery of sea otters (Enhydra lutris) has provided abundant evidence of the consequences of their local extinction from kelp forest communities in the North Pacifc Ocean. These consequences include release of benthic invertebrate populations from limitation by predation; deforestation of kelp beds due to increased grazing by herbivorous sea urchins, one of the otter's main prey; and various cascading effects resulting from the biological and physical importance of kelp in coastal ecosystems. These interactions probably were important agents of selection for certain species. Two other examples are discussed: Steller's sea cow (Hydrodamalis gigas), a case of global extinction, and spiny lobsters, a possible case of ecological extinction. We speculate that grazing by sea cows was an important disturbance to surface-canopy-forming kelps and other algae in the littoral zones, but also point out that any such interactions probably acted in concert with physical disturbances by ocean waves. The ecological and evolutionary importance of sea cow grazing probably will remain a matter of speculation and conjecture because the species is globally extinct. Predation by spiny lobsters limits a variety of littoral and sublittoral invertebrate populations, particularly mollusks In one remarkable example, the reduction or local extinction of spiny lobsters enabled predutory whelks to increase in size and abundance, ultimately resulting in a predutor-prey role reversal. From these and other case studies we can clued that (1) the extinction of consumers may have brad and sometimes unexpected influences on kelp forest ecosystems; (2) direct or indirect interactions with now-extinct species probably exerted important selective influences on many extant forms; (3) such ecological and evolutionary influences are best understood where local or ecological extinctions, followed by recoveries, have provided comparisons in space or time; and (4) because of various ecological and behavioral barriers, local extinctions and their ecological consequences may not be simply reversed by protecting or reintroducing depleted or locally extinct species.
The Pacific pond turtle (Clemmys marmorata) is a widespread aquatic turtle in the Pacific states, yet relatively little is known about its ecology. We radio-tracked 34 individuals during an 8 year period in 4 small coastal creeks in central California to determine their use of terrestrial upland habitats. Most of our turtles left the drying arroyos during late summer and returned after winter floods. Turtles spent an average of 111 days at these land refuges, which were located in woodland and coastal sage scrub habitats an average of 50 m from arroyos. Most gravid females left the creeks during June to oviposit in sunny upland habitats with low vegetation structure, such as grazed pastures. Nest sites were an average of 28 m from creeks. Terrestrial basking sites averaged 4.5 m from streams, but were only used for a few days. We believe the use of terrestrial upland sites was related to the Mediterranean climate and the resulting unique hydrodynamics of the small coastal arroyos (dry in summer and flooding in winter).
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The nearshore coastal areas of Belize and of Chetumal Bay, Mexico, support one of the largest populations of manatees ( Trichechus manatus manatus ) in the Caribbean. In order to further document the distribution, relative abundance, habitat associations, and status of this population, we conducted three aerial surveys. The flights were done in January 1994, May 1994, and January 1995. Total manatee counts for each survey were 266, 207, and 171, respectively. Calves represented 7.4% of the grand total. Solitary manatees represented 62.8% of the total count. Manatees were numerous around the cays east of Belize City, in Placentia and Indian Hill lagoons, and in Chetumal Bay. Most manatees were observed in lagoons and rivers. Growing tourist activities should be assessed to avoid undesirable effects on manatees. Poaching and marketing of manatee products continues to jeopardize the animals in some areas. Current research and management activities are part of a cooperative international program to conserve the manatee in the Caribbean region.
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To study burrow use by small mammals, we needed to develop a simple, non-invasive radiotag for the endangered giant kangaroo rat (Dipodomys ingens). We designed and tested a radiocollar made of beaded-chain on 4 captive Heermann's kangaroo rats (D. heermanii). Attachment of the collar required no anesthesia, the collar was easily fitted in 1-2 minutes, and it caused minimal stress to the animals. Once the collar design and attachment technique were perfected on the surrogate animals, we fitted radiocollars on 48 giant kangaroo rats for about 15 days. Upon recapture, 12 animals showed some minor fur or skin abrasion on the neck. Overall, the attachment performed as expected and proved to be a reliable method to radiotrack kangaroo rats during our short-term field study.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.