3.18.1 Biological characteristics
3.18.2 Available biological data
The 30 key groups or species of Latin American game animals are widely distributed throughout the neotropics (Table 22). Only three, Dasypus novemcinctus, Odocoileus virginianus and Sylvilagus floridanus are widely distributed in North America as well, and only the genera Geochelone and Dendrocygna are also common in the old world tropics. Tayassu tajacu and Trichechus manatus are also found as far north as the southern United States. Myocastor coypus, introduced into areas of North America and Europe, has formed major populations in some regions. The remainder of the game species are exclusive to Latin America and guidelines for their respective management and for research must be developed entirely within the region.
188.8.131.52 Habitat and diet
184.108.40.206 Seasonal reproduction
220.127.116.11 Life history strategies
18.104.22.168 Current status
The key groups and species present a broad diversity of biological traits. Most are medium-sized, and only three terrestrial mammals have adult weights of over 100 kg. North America has 11 big game mammals, including Odocoileus virginianus which grows much larger in the north.
Some species or groups exhibit fairly marked sexual dimorphism, enabling selective harvesting by sex. Some examples are Podocnemis, Geochelone, the iguanas, Caiman, Cairina and some Crax species, certain primates, the Cervidae, and, to a lesser extent, Hydrochaeris. Careful observations of social behaviour can also permit sexual differentiation of wild camelids in the Andean altiplano and in southern South America. Field identification of most game animals by sex is, however, virtually impossible.
The species listed in Table 27 are relatively sedentary, excepting Podocnemis expansa, Dendrocygna. Tayassu pecari and Lama guanicoe in certain localities. The sedentary habits of most game should facilitate local-scale management.
Most of the key groups and species are forest-dwellers (12), aquatic (6), of mixed or secondary habitats (6), or found in wetlands (4). Only two, the guanaco and the vicuña, typically live in open habitats. Except for the big carnivores, forest-dwellers and some of the aquatic species are usually partially or wholly frugivores, e.g. Podocnemis, Geochelone, Penelope. Crax, many of the primates, Tayassu, Odocoileus. Mazama, Agouti and Dasyprocta. This dietary preference is also shared by quite a few birds and mammals. As a result, the diversity of fruit, and the phenological aspects of fruit production and availability, are crucial factors for wildlife and deserve top priority in any review of wildlife habitats.
Table 27. Summary of selected biological characteristics of the key groups and species: adult weight interval, principal habitat type, interval of population densities reported, age (years) at sexual maturity (females), annual rate of reproduction, litter or clutch size, periodicity of reproduction (SEA == seasonal, CONT. = apparently continuous breeding, MAX. = continuous breeding but more intense at some seasons, general status (00 = endangered, 0 = vulnerable, 1 = scarce, 2 = common and 3 = locally abundant). Source: Bibliography cited in key groups and species.
The reproductive periodicity of the key species is only partially known, apparently varying greatly from one species and from one place to the next. Seasonal reproduction in some reptiles is clearly defined, e.g. Podocnemis, Iguana and Ctenosaura. They lay their eggs during the dry season and the clutches hatch with the onset of the rains. Most birds nest during the rainy season but the length of the breeding season often varies from one place to the next. Wild camelids breed on a seasonal basis in the spring or at the onset of summer in the southern hemisphere. A whole series of animals including Caiman, Pteronura, Felis pardalis, Mazama and Hydrochaeris exhibit peak sexual activity during the wet season with birth peaks during the transitional period preceding the dry season. Quite a number of these species also breed at other times of the year as well.
A considerable number of species apparently breed year-round. This includes both big mammals (Panthera, Trichechus, Tapirus, Tayassu, Odocoileus). and medium-sized ones such as Agouti, Dasyprocta. Myoprocta, Sylvilagus. Some tend to breed more during a specific season. It has been postulated, for example, that Trichechus inunguis and Tapirus terrestris are more apt to give birth during the rainy season. Also, the northernmost and southernmost populations exposed to seasonal temperature swings seem to have a more clearly-defined breeding season than their tropical conspecifics.
Future research into this matter is likely to reveal one or several seasons in which mammalian births are more frequent for species and sites where now, under present conditions, they seem to be out of phase. Even so, the breeding chronology of neotropical wildlife clearly presents a much more complicated picture than in the temperate climes. This makes it very difficult to work out hunting seasons that do not overlap with breeding seasons. It also suggests a need for more detailed regionalization of hunting timetables than is currently the case.
Life history strategies are also intimately linked with breeding and management options. Our current state of knowledge is barely sufficient to allow even a tentative approach to this important topic.
Looking at the list of breeding statistics in Table 27, we note a series of long-lived species which reach sexual maturity late and are generally not very prolific, but which do live long lives in the wild under favourable conditions. Into this category we can put Podocnemis, Geochelone, Caiman, Penelope, Crax, the big primates, Pteronura, Panthera, Trichechus and Tapirus. Within their taxonomic groups these species are usually the largest ones. They are also alike in that they are closely dependent on primary habitats, whether aquatic or forest. They are well-adapted to their own primary ecosystems and can maintain stable populations and achieve high biomass in their native habitats. In ecology this is known as the strategy of K-selection. At the same time, K-selected species are not tolerant of habitat modification, and their low reproductive capacity makes them extremely sensitive to increased adult mortality from hunting. Managing these populations through sustained harvesting is therefore extremely difficult and would depend entirely on stringent conservation measures in the primary habitat. Additionally, these animals are usually the largest and preferred game animals in their respective ecosystems, and therefore those most affected by commercial and subsistence hunting. Many representatives of this category are critically scarce: 10 of the 11 vulnerable or endangered taxa in Table 27 answer to the profile of K-selected species.
The opposite strategy is typical of some of the fairly prolific game animals, usually much less selective and much more flexible as to habitat, such as Dendrocygna, Sylvilagus and Myocastor, among the key species. Other game animals exemplifying this strategy are some dove species of the genera Columba and Zenaida, partridges (Colinus), spotted tinamous (Noctura maculata), hares (Lepus) and European rabbits (Oryctolagus). They live in open areas, mosaics of wooded and open areas, or in wetlands, and often successfully invade heavily modified habitats. They are generally much shorter-lived than the K-selected species and there may be sharp fluctuations in abundance. Animals with this type of life history are known as R-selected species. They are generally tolerant of moderate hunting pressures, which are partially offset by their high natural mortality rate. None of the species in this category is under serious threat, but some may be locally scarce. Generally speaking, the response to management is good and these are productive species, particularly in modified environments.
Obviously, K selection and r selection represent the two poles of a range of intermediate situations, probably covering most of the game animals in the region dealt with here. It is true of the ones that contribute most to the human diet such as Dasypus, Tayassu, Odocoileus, Mazama, Hydrochaeris, Agouti and Dasyprocta. Odocoileus americana, for its excellent ability to adapt to different kinds of habitat, is also in this category. The reproductive capacity of the two Tayassu species are also similar, if the available data are to be relied upon. Despite this, the management prospects for T. tajacu are much more promising than for T. pecari because T. pecari is highly mobile and requires vast and unbroken tracts of primary forest. As these few examples show, life history strategies can be a useful classification but the management of individual species demands specific planning geared to species biology.
The current status of the key groups and species compared in the last column of Table 27 is highly variable. Several species are currently in a very tight spot, whereas others, while scarce in some areas, can be common or abundant in others. Clearly, the prime management option for each local population and/or species depends on its status. Thinking along these lines, the sole immediate management objective should be to guarantee survival, and, where possible, secure the recovery of all vulnerable and endangered species and/or populations. For scarce but still not imperilled populations such as Geochelone, many iguana populations, Caiman crocodilus, Cairina, the cracids, various primates, Tapirus and many populations of Tayassu, Lama guanicoe, Odocoileus, Mazama and the big rodents, the priority objective should be to avoid degradation and to re-establish abundance and productivity at levels compatible with land use in each case. Finally, where there are solid indications that a species or population is common or abundant, the conditions will obtain for utilization for the maximum collective benefit, subject to the principle of sustainable harvest, constant monitoring and any necessary changes in order to conserve resource productivity. This objective may be applicable, for example, for certain iguana populations, Caiman, Dendrocygna, Dasypus, Tayassu, Lama guanicoe, Odocoileus, Mazama, Hydrochaeris, Agouti, Dasyprocta, Myocastor and Sylvilagus.
22.214.171.124 Classifying the available information
126.96.36.199 Biological aspects
188.8.131.52 Species biology
A fundamental condition of wildlife management is knowledge of species biology. However, there is no consensus as to the amount and type of biological documentation required to undertake a management plan. The more conservation-minded take the view that no utilization of wildlife is admissible unless in-depth and exhaustive data exists on the species it is proposed to manage. Partisans of quick solutions, on the other hand, allege that in most cases there is now enough available knowledge to form the basis of experimental management plans. Research, designed to go hand-in-hand with the experimental plan, would also include monitoring of the plan as a fundamental component, according to this view.
Both ways of thinking make sense, but in terms of practical implementation they may not be wholly compatible with reality. The research implicit in the first option (inevitably prior, dedicated and lengthy research) is costly and rarely realized. This leads to a peremptory vagueness where wildlife is concerned, which in turn furthers unregulated, clandestine and often destructive resource utilization. The principal risk involved in the second option is that experimental norms become definitive before they are duly accompanied by research and monitoring, generating an imbalance between the dynamics of the resource and the standards for its utilization, and eventually leading to population decline and the failure of the management plan.
Two types of biological information are needed for the design of wildlife management plans: 1) a knowledge of the basic biology of the species applicable over large areas and, 2) local data on the abundance, condition, habitat and seasonality of each of the specific populations to be managed. This brief review primarily concerns the basic biology.
One extremely positive fact is the increasing number of publications and writing on Latin American wildlife (Figure 2). Within this information there is quite a range in terms of detail, reliability, and relevance for resource management. We therefore need to classify the information before we can properly review the current state of knowledge on the various species and their biology.
Most of the information now available is descriptive and/or anecdotal, based on the experiences, views or beliefs of hunters and campesinos, or on naturalists' accounts, observations of animals in captivity, and so forth (Category 1). This diffuse information is repeatedly cited but there is no way to check its origin and accuracy.
Figure 2. Increase in the number of neotropical wildlife research works from 1935-1985 following the five-year bibliographical distribution used in this study.
Formal, science-based research with clear objectives and a quantitative approach (Category 2) does already exist for some species. These studies on basic biology (mainly doctoral theses, such as references 31, 33, 34, 74, 78, 80, 107, 109, 126, 133, 148, 168, 189, 217, 236, 271, 312, 315, 353, 363, 367, 442, 450, 459, 488, 492, 503, 546, 555, 564, 567, 599) cover specific biological aspects of concrete populations. While the information they generate is sound, it may not be applicable to the management of these populations.
Another source of information is medium- or long-term programmes of management, monitoring and research that have produced sufficient biological data for the management of at least some populations (Category 3): e.g., the Peruvian and Chilean vicuña project, the capybara project in Venezuela, and river turtles in Brazil.
The interactions between wildlife populations, habitat and people are complex ones involving many aspects of wildlife biology. Some, however, are of more immediate utility for management than others: reliable estimates of abundance, population growth rates, net productivity, selection and carrying capacity of the habitat and periodicity of reproduction are of prime importance for any management plan. The order of priority for other factors may vary with the specific case. Mortality data are usually a priority for short-cycle species, whereas dispersion and social structure are much more important for the larger animals.
The quality and quantity of available data on the various biological aspects is quite variable, as the bottom line averages in Table 28 indicate. Reproductive biology, feeding habits, behaviour and other selected aspects of natural history are the best-covered. In some cases the data come exclusively from animals in captivity, and are thus of questionable application for wild populations.
Moreover, documentation concerning population aspects such as growth and regulation, natural mortality, net productivity, and various impacts of density-dependence are not at all well-known for most species and populations. Other factors of great practical value, such as the rate of individual growth, mobility and dispersion, and techniques for estimating population density have also received little attention. Hunting statistics and management plan monitoring statistics are habitually and widely under-utilized. A careful study of these data can be most useful in elucidating growth rates and other population responses to management plans. The relationships between wildlife and wildlife habitat are also not very well understood for the neotropics. Scientists are in the habit of describing the general structure and floral composition of their study area, but an in-depth analysis of how animal populations are dependent on the available habitat and which factors determine habitat selection, quality and carrying capacity is not part of the description.
The scant knowledge of the biological aspects most relevant for wildlife management would seem to indicate the predominance of academic objectives in the research done to date. At the same time, the situation would seem to suggest the advisability of setting applied research priorities in strict accordance with management plan objectives.
The biological information available for each species repeats the same highly variable pattern as above. As a group, primates have received a good deal of attention in recent years, and are now among the best-known neotropical animals from the biological standpoint. In addition to the primates, the most studied and best-known native Latin American species are the vicuña and the capybara. Both are dominant native herbivores in their respective ecosystems, of great importance in socio-economic terms, and currently the subject of long-range management plans. A substantial basic research effort, plus many years of management and monitoring, has provided fairly complete data which should enable careful decision-making for the management of these species. The biology of capybara along rivers in the forest regions is virtually unknown, however, as all of the current experience refers to open habitats.
The available information on the remaining key groups and species is rather more fragmentary, with both quality and quantity varying. The best-known turtle, thanks to various research projects set up in Brazil, Peru and Venezuela to document population trends and breeding, is Podocnemis expansa. However, very little is known about the ecology of P. expansa away from the nesting beaches. The very patchy data on land turtles (tortoises) comes mainly from observations of tortoises in captivity. The available information on iguanas is quite fragmentary, particularly population data. Ongoing projects in Costa Rica, Panama and Venezuela do, however, hold out the promise of new information in the near future. The natural history and some aspects of the population ecology of Caiman crocodilus have been elucidated in Brazil, Colombia, Peru and Venezuela. Population monitoring and captive breeding data are also available for vast areas of Venezuela, but neither the net productivity of C. crocodilus populations nor their density-dependence are known at this time.
The available information on whistling ducks (Dendrocygna) includes aspects of its basic natural history, hunting season data, and the results of an ongoing ringing programme in Venezuela. There is no specific field research data on Cairina moschata biology. The data on cracids, summarized in 153 and 186, with evaluations of some highly endangered species and experience in aviaries, is also very general. Various research projects now underway, particularly in Venezuela, will be providing further information to guide cracid management.
Table 28. Evaluation of the current status of biological data on the key species: 0 = no information whatsoever, 1 = anecdotal information, 2 = at least one quantitative study, 3 = satisfactory level of information. The figures in parentheses refer to research studies in captivity and/or not done in Latin America
Table 28. Evaluation of the current status of biological data on the key species: 0 = no information whatsoever, 1 = anecdotal information, 2 = at least one quantitative study, 3 = satisfactory level of information. The figures in parentheses refer to research studies in captivity and/or not done in Latin America (cont.)
As for the mammals, almost nothing is known about the biology of Dasypus novemcinctus in tropical America: the applicability of information from North America to management in Latin America is very much open to question. There is some recent research work on the endangered carnivores: Pteronura (67, 168, 327), Felis pardalis (181, 353) and Panthera onca (181, 406, 487, 521) that may provide some guidelines for plans to recover the populations of these species, but much study is still needed on the population aspects. Most of the biological data on manatees comes from Florida in the United States and from the Brazilian Amazon. However, due to the difficulties inherent in studying manatees, many aspects such as those concerning breeding remain unknown. Virtually the only information available on the South American tapir is anecdotal or comes from observations in captivity, and little or nothing is known about the ecology of this species in the wild. The same can be said of Tayassu pecari, the prime subsistence hunting target in forest areas. The data from field reconnaissance operations in Brazil (520), Paraguay (372) and Peru (315) are so very incomplete that there is an urgent need for in-depth research on the wild populations of these two ungulates. The situation for Tayassu tajacu is quite different: a great deal of information is available from the southeastern United States. Summarized by Sowls (560), it can supplement the data collected in Latin America. For now, very little is known about T. tajacu's reproduction, productivity and relations with the habitat. The existing information on guanaco ecology is not as extensive as that on vicuña. The most exhaustive research on guanaco was done in Magallanes (488) in a project that covered most of the relevant factors for the management of this population.
The case of the white-tailed deer Odocoileus virginianus is much like that of the collared peccary. White-tailed deer biology is well-documented in North America and some of the information is applicable to Latin America, particularly Mexico. Field research has also been done on the species in Mexico, Suriname and Venezuela. The documentation is therefore fairly representative. The general picture of O. virginianus's reproductive periodicity is blurred, however, and very little is known about the species' abundance and natural mortality, and the carrying capacity of its habitats. The available data on Mazama americana, the dominant neotropical forest deer, is limited to a very recent study in Suriname (73-75) concentrating on the breeding and feeding of this species. Likewise, almost all of the information on the ecology of wild populations of the paca (Agouti paca) and the agouti (Dasyprocta) come from a single study for each (126, 546). There is also data on the breeding of animals maintained in captivity. The ecological research on the agouti was done in Barro Colorado Island, Panama, where there are excessive numbers of these rodents, and so the findings of the study are inevitably not representative of normal Dasyprocta populations. Clearly, what we know about the biology of these rodents is very little compared to their value as game animals. Most of the available data on coypu (Myocastor coypus) comes from the United States and from European countries where this rodent has been introduced and may even be considered a pest. Field research in South America is neither sufficient nor adequate for serious management of this valuable South American rodent. The same is true of the native rabbit Sylvilagus floridanus, the biology of which is well-documented in North America. The initial research done in South America (434, 450, 564) shows considerable ecological differences compared to S. floridanus's northern conspecifics, suggesting that findings from other latitudes may have little bearing on the tropics.
Generally speaking and in conclusion, while more and more biological data is available on the main game animals of Latin America, the data on species and geographical areas and the biological specifics are still very patchy. The predominant focus continues to be natural history, with population dynamics and relations with the habitat remaining in the background. Most of the fundamental contributions on the subject concern individual academic initiatives, i.e. university theses. It is often difficult for wildlife administrators to gain access to this information, particularly to papers done by foreign researchers. Another thing is that research usually concentrates on protected areas where wildlife population densities and overall ecology may well be quite unrepresentative of the region as a whole. With few exceptions, the government agencies responsible for wildlife affairs lack a coherent research policy focusing on the priority biological considerations from the management standpoint. The scarcity of biological data is therefore a serious constraint to the development of management plans. This is particularly true for Geochelone, Dasypus, Tapirus, Tayassu pecari, Mazama and Agouti for which very little is known in population terms, despite their significant contribution to the human diet in forest areas.