A computer simulation program was used to examine interacting effects of genetic drift, mutation, immigration from outside populations, directional and balancing selection, and population subdivision on the loss of genetic variability from small, managed populations. Stochastic events were simulated with a pseudo-random number generator, and the genetic variation (expected heterozygosity) within and between populations was monitored in 25 populations for 100 generations. Genetic drift was the overriding factor controling the loss of genetic variation. Mutation has no noticeable effect on populations of the size typically managed in zoos and nature preserves. Immigration from a large source population can strikingly slow, halt, or even reverse the loss of genetic variation, even with only one or a few migrants per generation. Unless selection is stronger than commonly observed in natural populations, it is inefficient in countering drift when population sizes are on the order of 100 or fewer. Subdivided populations rapidly lose variability from within each sub-population but retain variation across the subpopulations better than does a panmictic population. These results suggest that population managers should be concerned with the variation-depleting effects of genetic drift, perhaps almost to the exclusion of consideration of selection and mutation. Drift can be countered by the introduction of very occasional immigrants or, less effectively, by division of the managed population into smaller breeding groups that interchange enough migrants to prevent unacceptably deleterious inbreeding within each subpopulation.
There are few controlled data with which to assess the conservation role of corridors connecting refuges. If corridors were used sufficiently, they could alleviate threats from inbreeding depression and demographic stochasticity. For species that require more resources than are available in single refuges, a network of refuges connected by corridors may allow persistence. Finally, a corridor, such as a riparian forest, may constitute an important habitat in its own right. A dearth of information on the degree to which different species use corridors makes it difficult to tell which of these potential advantages will be realized in any particular case. Some experimental field studies suggest that certain species will use corridors, although lack of controls usually precludes a firm statement that corridors will prevent extinction. Corridors may have costs as well as potential benefits. They may transmit contagious diseases, fires, and other catastrophes, and they may increase exposure of animals to predators, domestic animals, and poachers. Corridors also bear economic costs. For example, a bridge that would maintain a riparian corridor costs about 13 times as much per lane-mile as would a road that would sever the corridor. Also, per-unit-area management costs may be larger for corridors than for refuges. It may be cheaper to manage some species by moving individuals between refuges rather than by buying and maintaining corridors. Each case must be judged on its own merits because species-environment interactions differ. As an example, we used the case of the Florida panther (Felis concolor coryi), of which there remain about 30. The Florida panther's potential inbreeding problems could possibly be stemmed somewhat by a corridor system, but it is far from certain that even an extensive system will save this animal, and the cost of such a system would lessen the resources that could be devoted to land acquisition and other means of aiding many other threatened species.
The nested subset hypothesis states that the species comprising a depauperate insular biota are a proper subset of those in richer biotas, and that an archipelago of such biotas, ranked by species richness, presents a nested series. The pattern characterizes the distributions of mammals in three different archipelagos, and it appears more strongly developed among faunas in the process of relaxation (landbridge islands) than in those derived by overwater colonization (oceanic islands). The generality of the nested subset pattern and factors that may produce it are evaluated using distributions of land birds in the New Zealand region. Monte Carlo simulations show that species composition of these insular avifaunas is highly nonrandom, exhibiting significantly nested structure. However, avifaunas on nine oceanic islands lack the structure typical of all islands together or of the 22 landbridge islands. Thus, distinctive patterns of species composition, as well as species number, may distinguish landbridge and oceanic islands. Because they are isolated fragments of once-continuous distributions, landbridge islands and their biotas have important implications for long-term biological conservation in preserves. Real or virtual islands that have undergone faunal relaxation support only a fraction of the species expected in equivalent mainland areas. Furthermore, the species inhabiting fragments are not a random collection of those in the source pool, but are rather nested subsets of the species in richer, more intact biotas. The species preserved in such fragments tend to be the most abundant, generalist species that are least in need of special protection.
Habitat corridors have become popular in land-use plans and conservation strategies, yet few data are available to either support or refute their value. Simberloff and Cox (1987) have criticized what they consider an uncritical acceptance of corridors in conservation planning. Any reasonable conservation strategy must address the overwhelming problem of habitat fragmentation. Although Simberloff and Cox use island analogies to illustrate advantages of isolation, these analogies do not apply directly to problems in landscape planning. Genetics also does not offer unequivocal advice, but the life histories of wide-ranging animals (e.g., the Florida panther) suggest that the maintenance or restoration of connectivity in the landscape is a prudent strategy. Translocation of individuals among reserves-considered by Simberloff and Cox a viable alternative to natural dispersalis impractical for whole communities of species that are likely to suffer from problems related to fragmentation. Many of the potential disadvantages of corridors could be avoided or mitigated by enlarging corridor width or by applying ecologically sound zoning regulations. Corridors are not the solution to all of our conservation problems, nor should they be used as a justification for small reserves. But corridors can be a cost-effective complement to the strategy of large and multiple reserves in real-life landscapes.
: Quantitative data are presented on the use of trees in terra firme dense forest by four indigenous Amazonian groups: the Ka'apor and Tembe, both Tupi‐Guarani‐speaking groups of Brazil; the Panare, a Cariban‐speaking group of Venezuela; and the Chácobo, a Panoan‐speaking group of Bolivia. In each case, an ethnoecological forest inventory was conducted of a 1‐hectare parcel of forest. All trees at least 10 centimeters diameter at breast height (DBH) were marked, and botanical specimens were collected Specimens were presented to indigenous informants to gather data on use. Based on these interviews and the identifcation of specimens collected, it was possible to calculate the percentage of tree species on each hectare that was useful to each group: Ka'apor, 768 percent; Tembe 61.3 percent; Panare, 48.6 percent; Chacobo, 78.7 percent. Furthermore, by dividing the trees into various use categories (food construction, technology, remedy, commerce, and other), and designating the cultural importance of each species as “major” or “minor,” it was possible to devise a “use value” for each species, and by summation, for each plant family. Based on these calculations, it was determined that the Palmae was the most useful family for all four indigenous groups. Our data support the assertion that the terra firme rainforests of Amazonia contain an exceptionally large number of useful species and that certain plant families (e.g. Palmae) deserve special consideration in terms of conservation. The fact that each indigenous group has different suites of most useful species is, in fact, more a reflection of plant endemism within Amazonia than intercultural differences per se. High indigenous plant use combined with high endemism has important implications for conservation policy: many reserves are needed throughout Amazonia Resumen: Se presentan datos cuantitativos sobre el uso de aárboles en bosques densos de terra firme, por cuatro grupos de indígenas amazónicos: los Ka'apor y los Termbé brasileños de la familia lingüística Tupi‐Guarani; los Panare, venezolanos de la familia lingüística Cariban; y los Chácobo, bolivianos de la familia lingüística Panoan. En cada uno de los casos se hizo un inventario forestal etnoecológico en una parcela de bosque de una hectárea; se marcaron todos los aárboles depor lo menos 10 cm de diámetro a la altura del pecho (DAP), se colectaron muestras botánicas y se mostraron a los indigenas para obtener datos acerca de su uso. Basados en las entrevistas y la identificación de los especimenes colectados fue posible calcular los siguientes porcentajes de especies arboreas utiles para cada grupo: 768% para los Ka'apor, 61.3% para los Tembe, 48.6% para los Panare y 78.7% para los Chácobo. Además, dividiendo los árboles en varias categories de uso (alimento, construcción, tecnologia, medicina, comercio y otros), y designando la importancia cultural de cada especie como “mayor” o “menor” fue posible estimar un “valor de uso” para cada especie y un “valor total” para cada familia de plantas. Estos datos indican que la familia Palmae era la más útil para los cuatro grupos. Nuestros datos sustentan la afirmación de que los bosques lluviosos de terra firme contienen un numero excepcionalmente grande de especies ütiles y que ciertas familias de plantas (e.g, Palmae) merecen especial atención en términos de conservación. El hecho de que cada grupo indigena tenga diferentes colecciones de especies es más un reflejo de endémismo vegetal en la Amazonid que diferencias interculturales per se. El gran uso de plantas nativas combinado con el alto endemismo tiene implicaciones para la politica de conservación: se necesitan muchas resmas a través de la Amazonia.
An original difficulty in accepting the idea of a pelagic developmental period for sea turtles was to explain how food could be found in reliable supply in the open ocean. The uncertainty that this introduced was removed when I belatedly came to appreciate the prevalence and diversity of convergences where downwelling gathers and aligns buoyant material, including the dispersed food resources of the surface waters. Thus, it now seems clear that an essential factor in the survival of young sea turtles-and of other elements of the epipelagic, open-ocean fauna as well-is the accessibility of a front, where inanimate debris and any floating animal or plant will be gathered in. This new evidence of complexity in the lost-year ecology of sea turtles has important implications for their conservation and management. It is now obvious that when young cultured sea turtles are released in so-called head-starting projects, the release sites ought to be chosen with the greatest care. Shores located at a distance from any major current or its eddy ought to be avoided. It is also necessary to avoid release localities where the convergence habitat may carry heavy loads of pollutants. Results of the present work reveal an urgent need for further study of sea turtle life cycles, with special attention to their developmental ecology. The growing evidence for a more protracted pelagic stage, during which the juvenile turtles are passive migrants in fronts that are increasingly invaded by debris and toxic wastes, emphasizes the need for a better understanding, by marine biologists, of the organization of the driftline habitat and the behavioral ecology of its occupants. Until these studies of the oceanography and biology of driftlines are done, we are bound to remain peculiarly ignorant of the ecologic organization of three-fifths of the surface of the earth.
The effect of the spatial structure of populations on extinction rates is a central question in conservation biology, ecology, and evolution. We show that the effect of subdivision on the mean time to extinction in independently varying habitat patches depends upon the relationship between extinction probabilities and habitat area. Models of extinction by demographic stochasticity alone predict that subdivision should decrease the mean time to extinction. If environmental stochasticity is incorporated into the model, subdivision may increase the mean time to extinction. Empirical species persistence times estimated from island biogeography studies show no systematic relationship to the degree of subdivision. However, subdivision always increases the probability of survival over a sufficiently short time interval. These results suggest that over ecologically relevant timescales, subdivision into a number of independent subpopulations may frequently act to decrease the probability of overall extinction in rare species. To the degree that these considerations may be applied to rare and endangered species, maintaining sufficient numbers of nature reserves is likely to be crucial to effective conservation strategies.
Differential extinction of forest species following forest fragmentation raises the questions of which populations are most prone to disappear, and why. Hence we studied an 86-hectare woodland in west Java, the Bogor Botanical Garden (BBG), that became isolated when surrounding woodland was destroyed 50 years ago. Out of 62 bird species breeding in the BBG during 1932-1952, 20 had disappeared by 1980-1985, four were close to extinction, and five more had declined noticeably. The two main variables that identify extinction-prone populations in the BBG are 1) small initial population size in the BBG and 2) rareness or absence in the surrounding countryside. Although the BBG retained wooded habitat, it is evidently too small to retain self-sustaining populations of many woodland bird species. Small populations at high risk of extinction for stochastic reasons are doomed to disappear permanently unless subsidized by recolonization from the surroundings. Thus, a too-small reserve cannot function as a distributional island but comes to mirror the species composition of its surroundings. More such case studies documenting species losses from small habitat fragments are required to demonstrate to nonbiologists the need for reserves large enough to support self-sustaining populations.
Peasant agroecosystems are seen as a continuum of integrated farming units and natural ecosystems where plant gathering and crop production are actively practiced. Many of these traditional agroecosystems still found throughout developing countries constitute major in situ repositories of both crop and wild plant germplasm. These plant resources are directly dependent upon management by human groups; thus, they have evolved in part under the influence of farming practices shaped by particular cultures. Because genetic conservation programs are more effective when preserving the ecosystems in which the resources occur, maintenance of traditional farming systems and adjacent natural ecosystems is proposed as a sensible strategy for in situ preservation of crop and wild plant genetic resources. It is here argued that preservation efforts should be linked to rural development projects that take into account the ethnobotanical knowledge of rural people and that emphasize both food self-sufficiency as well as local resource conservation. Preservation of these traditional agroecosystems cannot be achieved when isolated from maintenance of the culture of the local people. Therefore, projects should also emphasize maintenance of cultural diversity.
Long-term studies of checkerspot butterflies (Euphydryas spp.) are used to draw conservation lessons with implications for the design and management of reserves for invertebrates. We discuss; 1. The importance of determining the structure of and patterns of mating within demographic units. 2. The lack of congruence between migration and gene flow. 3. The crucial role of habitat diversity in the protection of species which otherwise require only small areas of habitat. 4. The importance of identifying and preserving "reservoir" populations within metapopulations. 5. The necessity of identifying subtle habitat requirements. 6. The key role of environmental stochasticity in the extinction of small populations. 7. The difficulty of protecting metapopulations and of introducing populations into "empty" habitat patches. We conclude, among other things, that the size of reserves required to preserve herbivorous insects is often underestimated; that a "minimum viable metapopulation" approach to their conservation may be needed; that long-term studies of the biology of populations of sample invertebrate groups would greatly aid conservation biologists; and that more effort is needed to inform the public and decision makers about the need to conserve populations as well as species.
Endemic species are commonly hypothesized to have little genetic variation because of inbreeding, genetic bottlenecks, and/or other factors. We investigated genetic variation in Pedicularis furbishiae (Scrophulariaceae), an endangered endemic of the St. John River valley in northern Maine, by examining electrophoretic patterns at 22 loci in 28 individuals distributed among four populations. No variation appeared at any of the loci, although this sample was sufficient to detect any variant alleles with a frequency of 5.2 percent or more with 95 percent probability. This lack of variation is probably due to founder effects accompanying the original postglacial establishment and subsequent repeated episodes of population establishment and local extinction along the St. John.
International economic development projects speed deforestation in Brazil's Amazon region. Highways financed by these projects form a key link in a positive feedback relationship between deforestation and population migration. Roads facilitate entry of settlers whose land claims (established by deforestation) justify building more roads. Deforestation is explosive in Rondonia, site of the World Bank-financed POLONOROESTE project. Increased deforestation is likely in Acre, where highway improvement financed by the Interamerican Development Bank is under way, and (if funded) in the Grande Carajas agricultural program area. Deforested areas are usually converted to low-diversity cattle pasture to secure land claims at minimal cost. Pasture also facilitates obtaining land titles. Profits from land sales are enhanced by road improvements and by titling. Government and development project efforts to encourage nonpasture uses are unlikely to be effective in the absence of reforms limiting the profitability of land speculation. Economic development projects in Brazilian Amazonia share many common patterns that lead to heavy impact on the region's natural ecosystems. High-level decisions make the projects irreversible before environmental and land capability studies are madeor even in spite of negative indications that are already known. Previous commitments to preserving natural habitats and tribal areas are frequently reneged. Environmental measures are often mere symbolic actions serving only to tranquilize public concern during the key period when the development is not yet a fait accompli. Projects in Amazonia are often undertaken to alleviate social problems outside the region, especially by absorbing migrants who leave southern and northeastern Brazil because of population growth, agricultural transformation, and land tenure concentration. If they are to be effective, measures addressing these problems must be applied directly in the migrant source areas. Financing Brazil's agrarian reform efforts in these areas represents a major opportunity for international lending agencies to help slow Amozonian deforestation.
An understanding of vegetation dynamics is basic to the manipulation of plant communities. Traditional succession/climax concepts can often hinder rather than aid in sound vegetation management. In interpreting vegetation change, a diverse set of factors is often operative. Certain of theseinitial floristic composition and the tolerance, facilitation, and inhibition modelsare specifically related to the basic processes involved in vegetation or biotic change and to specific management problems. For example, certain shrublands within forested regions can exhibit remarkable resistance to tree invasion, a phenomenon especially relevant in managing rights-of-way, naturalistic landscape areas, and wildlife habitats and in maintaining landscape diversity. Fire and herbicides are also important management tools in the restoration and perpetuation of certain community types. Because natural disturbances are critical in maintaining landscape diversity, the incorporation of natural areas should be a part of every land-use management plan. Because wetlands are pulsed systems, succession and climax concepts are often of limited usefulness, that is, wetland vegetation belting is often erroneously interpreted as succession. Considering the diverse interpretations of these traditional concepts, a new paradigm is needed. To give a more holistic view of biotic or ecosystem change, the appellations vegetational or biotic development are proposed to replace succession, and steady state and relative stability are offered as more realistic terms than climax.
We are well aware of the main mechanisms of extinction, especially those which derive from human activities. But these mechanisms tend to be studied in isolation from each other. We know much less and understand less still about the dynamic interplay between the discrete mechanisms. When we consider the likely outcome of several mechanisms operating at once, we can reasonably surmise that many of their effects will serve to amplify each other. These synergistic interactions are the subject of this exploratory paper. It is proposed that synergisms between discrete mechanisms, working collectively and with compounding impact on each other, will surely lead to a greater scale extinction episode ultimately. In the more immediate term, they may cause the episode to be telescoped in its time frame, especially in the early phases. This means that a large-scale elimination of species may occur even sooner than some observers anticipate. To the extent that this is so, there is all the greater premium on anticipatory planning and conservation measure, to be taken with due urgency.
Recent reformulation of the birth-and-death process model to include the effects of environmental variation on stochastic demography presents a pessimistic view of the prospects for persistence of small populations. The models indicate that modest increases in population size, or in the mean (positive) growth rate of the population, do not dramatically increase the mean persistence time. The key to long-term persistence seems to lie in reducing the variance in the population growth rate. Natural populations, of those species that are not numerous, achieve their persistence through a variety of variance-reduction mechanisms. These notably include: 1) risk-averaging by wide geographic distribution over areas that experience mutually independent environmental variation, and 2) reliance on restricted "hot spots" of especially favorable habitat where the local population growth rate is almost invariably strongly positive when the population is not crowded. These natural mechanisms depend on a spatial scale, and on species-specific richness of habitat, which is not readily attained for many species on biological reserves with a "hands-off" management policy. However, these mechanisms can be mimicked by management intervention strategiesparticularly by reintroduction programs in an "archipelago" of geographically dispersed reserves that are otherwise mutually isolated, and by resource augmentation, predator and disease control, and other survival-and-reproduction enhancement programs implemented specifically at times when the population is at a low ebb.
: During the course of a recent compilation of information concerning the natural history of Sulawesi, Indonesia, it became apparent that there were no recent records of the endemic Caerulean paradise‐flycatcher Eutrichomyias rowleyi and few of the endemic species of the fish family Adrianichthyidae. Efforts were made to confirm the continued existence of these animals but without success, and while it is impossible to be certain, we suggest that these species, and perhaps others from their communities, may be extinct or iritically endangered It is of great concern that none of the species discussed has ever been mentioned in the IUCNRed Data books, and it is suggested that further species in the endemic‐rich area ofWallacea may also have become extinct in the last few decades. Resumen: Durante el curso del la mhs reciente recopilación de información sobre la historia natural de Sulawesi, Indonesia, se hizo obvio la falta de datos actualizados sobre el ave endémica Caerulean Paradise‐flycatcher Eutrichornyas rowleyi y los pocos datos existentes sobre las especies endémicas de la familia de peces Adrianichthyidae. Sin éxito alguno se ha tratado de confirmar la existencia de estos animales, y mientras es imposible estar seguro de esto, nos atrevemos a sugerir que estas especies, y quizá otras de las mismas comunidades, se encuentran extintas o críticamente amenadas. También es alarmante que ninguna de estas especies a las que nos referimos hayan sido mencionadas en el Libro Rojo de la IUCN, y nos atrevemos a manifestar que otras especies de la rica y endémica área de Wallacea tambié hayan desaparecido en las últimas decadas.