Additionally, even with equalizing family sizes after wild exposure, the benefits of exposing genotypes within families to natural selection would still be gained. Furthermore, the disproportionate use of individuals from better-surviving families for generating the new broodstock would result in an irreversible loss of genetic diversity. Some families would be under-represented and others potentially not represented at all. Such diversity may be important for the population to respond to future environmental change.
Disproportionately using individuals from families with a greater fitness performance is most in line with what existing conditions in the wild can support. This practice should improve the likelihood that the reintroduced population will become self-sustaining. Captive-bred families favored by natural selection in the wild this year or the next might not be those favored several years or a decade down the road.
Cryopreserved sperm obtained from males in the founder or early generations of captivity could also be used to fertilize female eggs in subsequent generations Sonesson et al. This practice could mitigate the loss of fitness in captivity due to domestication selection or the relaxation of natural selection in captivity, by minimizing captive generations before reintroduction in the wild. The technique has been initiated in recently commenced live-gene banking programs of Atlantic salmon in Norway and Canada O'Reilly and Doyle , but like any tool, it has disadvantages that merit consideration as well discussed below.
Allowing captive-reared adults, or adults that have had some degree of captive-rearing, to also breed in the wild and thus have free mate choice, may generate offspring that have benefitted from sexual selection and whose parents have had exposure to natural breeding conditions and breeding grounds Berejikian et al. The procedure is currently being attempted as part of some Pacific salmon captive breeding programs Berejikian et al.
Increasingly, hatchery-rearing procedures or environments are also being modified to more closely resemble the natural environment. Modifications include reduced juvenile densities, overhead or submerged cover, naturally coloured substrate, antipredator behavior conditioning, subsurface rather than overhead feeding, and even net-pen rearing in natural environments Maynard et al.
Reisenbichler pointed out that the effects of seminatural environments on potentially reducing domestication selection have not been empirically tested in salmonids, and he discussed two potential approaches for assessing this. Considerable uncertainty remains with respect to the short- and long-term fitness effects of captive breeding in salmonids, despite the numerous laboratory and field studies conducted to date on the performance of hatchery-reared and wild salmonids.
The most relevant studies to date also appear to have had limited statistical power to make general conclusions regarding whether or not one generation of captive-rearing can reduce fitness in the wild Araki et al. Caveats aside, the studies of Araki et al.
Furthermore, as discussed by Hard and Waples , the power of even the most ambitious monitoring programs to statistically detect a captive-breeding effect on phenotypic and life history traits is likely very low because natural variability in the same traits is very high. This means that the effects of captive-breeding might only be detected long after considerable harm to wild fish has occurred Waples On the other hand, for several reasons, the rate to which fitness was lost in Araki et al.
Interestingly, fitness reductions in hatchery-reared salmonids detected in laboratory studies were not as strong as the Araki study 2. Studies involving nonlocal hatchery fish also suggest that fitness reductions will become elevated with increasing generations of manipulation or rearing in the captive environment see also Araki et al. Indeed, many of the poorest performances of hatchery fish relative to wild fish involved nonlocal hatchery strains that had been in captivity for greater than five generations or that had undergone intentional artificial selection e.
Finally, a major issue meriting further debate and study pertains to the trade-offs between maintaining genetic diversity and fitness of captive broodstocks Box 2 ; see also the section below on whether to use single versus multiple facilities to conserve genetic diversity and fitness. For instance, there are clear fitness benefits to exposing individuals to existing conditions in the wild for some period of their lifecycle.
There are also clear benefits to equalizing family sizes after a period of wild exposure to maintain neutral genetic diversity. Yet, this may also reduce the fitness benefits that were accrued during the period of wild exposure. Reintroduction attempts of a variety of captive-reared endangered species or populations into the wild have historically had mixed success Griffith et al. Wolf et al. However, owing to the earlier dates in which a considerable portion of the studies within these reviews were conducted, many of these reintroduction attempts might have failed because the reintroduction programs did not account for all the prerequisites for success identified in later documentation, such as mitigating the factors originally leading to extirpation, behavioural deficiencies of the released animals, or improper release dates e.
Additionally, it has only been widely recognized more recently that domestication selection may affect reintroduction success Frankham et al. Thus, many historical captive breeding programs probably did not adopt procedures to reduce domestication selection or the loss of genetic diversity in captivity see Table 2. Seddon summarized a variety of definitions that have been considered regarding what constitutes a successful reintroduction.
The definitions put forth have included i breeding by the first-wild born generation, ii a breeding population with recruitment exceeding adult death rates for 3 years, iii an unsupported wild population of a minimum of individuals, iv establishment of a self-sustaining population Griffith et al.
Evidently, the applicability of any one criterion might be limited depending on the life history characteristics of the species targeted for reintroduction Seddon I define a self-sustaining population as a population that persists for multiple generations in the absence of any human intervention, such as supplementation, artificial habitat enhancement or any degree of captive breeding or genetic modification.
In many ways, this definition is most in line with one of the ultimate goals of captive-breeding programs; that is, to re-establish a species in an area which was once part of its historical range IUCN The definition is also formulated with the hope that self sustainability will represent the long-term persistence of the reintroduced species, but does not assume that self sustainability is equated with long-term persistence.
For instance, a salmonid population could be reintroduced as a self-sustaining population for several generations, but then a new threat might render it no longer viable e. I also considered this issue from four additional contexts. First, was there any evidence that hatchery-reared fish in supplementation programs provided net long-term benefits to wild salmonid populations?
These programs differ somewhat from reintroducing captive-reared salmonids into formerly occupied habitats, but they provide another context for assessing the potential for captive-reared lines to translate into self-sustaining populations. Third, how can one improve the chances of successful reintroduction if the wild environment has changed by the time the captive population can be reintroduced? Fourth, was there any indication that particular salmonid species or life-history types may be more difficult to reintroduce successfully?
This list of studies by no means should be viewed as exhaustive as undoubtedly, some other systems have been inadvertently overlooked. In 16 of 31 population systems, captive-breeding programs are too recent to assess whether they will ultimately be successful or not in translating into self-sustaining populations. In six of the remaining 15 systems, reintroductions have been unsuccessful at generating self-sustaining populations.
Reintroduction failures have occurred even after 30 years of reintroduction attempts in some cases Table 7. Reintroduction failure over this timeframe might not be too surprising given that many historical programs probably did not adopt procedures that are implemented in current captive breeding programs Table 2. However, the list of reintroduction failures also includes two captive breeding programs that incorporate many of these procedures e.
Importantly, not all of the obvious factors that were likely contributing to reintroduction failure had been removed in any of these six systems, regardless of whether current captive breeding procedures had or had not been adopted.
While these factors were often multifaceted, it is noteworthy that environmental changes to habitat were implicated in all six systems with unsuccessful reintroductions Table 7. Characteristics of salmonid reintroductions involving hatchery- or captive-reared fish. Conversely, there were no obvious habitat limitations in the nine population systems, where captive-breeding has led to apparently self-sustaining populations.
Yet, in one case, artificial liming of rivers was required to reduce acidification induced by acid rain so that Atlantic salmon populations inhabiting them could be self-sustaining Hesthagen and Larsen In another case, successful reintroduction of sockeye salmon populations might have been driven by dispersal and gene flow from neighboring, healthy wild populations and not necessarily by captive-reared fish Withler et al. In four other cases, reintroduced populations might be becoming self-sustaining but they are all still dependent on supplementation Spidle et al.
Environment Agency b , , Bosch et al. Consequently, there is little long-term evidence regarding whether captive-reared salmonids can or cannot be reintroduced as self-sustaining populations. This is either because i captive breeding programs that adopt a multitude of procedures to reduce domestication selection and the rate of loss of genetic diversity in captivity have been initiated too recently to assess the performance of captive releases in the wild, ii reintroduction failures were confounded by not having other threats removed that likely impeded reintroduction success, most notably, habitat loss or change, iii apparently successful reintroductions may have been confounded by other factors which could explain the success besides captive-breeding e.
This estimate is based on the realistic amount of time required to initiate a captive-breeding program, carry out reintroduction attempts, and monitor postrelease success after multiple generations. Waples et al. Most programs 17 of 22 used hatchery fish from the local wild population for supplementation, but their data had not previously been summarized and published in the primary literature.
For net long-term benefits to occur, Waples et al. Again, this situation is somewhat different from that of reintroducing captive-reared salmonids in an attempt to generate self-sustaining populations into formerly occupied habitats — it more typifies the situation where a captive-breeding program is initiated to supplement a rapidly declining population. Also, Waples et al. Bearing these caveats in mind, the major conclusions from the meta-analysis were as follows. Second, in the long-term, and in parallel to the observations and conclusions above, there is considerable uncertainty regarding the ability of supplementation programs to provide net long-term benefits to wild salmonid populations.
As a result, these authors highlighted that the lack of empirical demonstration that supplementation provides net long-term benefits to wild salmonids should be a cautionary note to those considering initiating new programs or continuing existing ones Waples et al. These patterns are interesting for two reasons. Second, where salmonids have historically been capable of dispersing naturally, they have colonized all habitats currently suitable to them.
The wild environment of captive salmonid populations might also change dramatically by the time fish can be reintroduced. The environment of the Bay may therefore be very different than that of say 15 to 20 years before its salmon populations collapsed, and these changes could have been the major reason for the collapse in the first place COSEWIC b. Krueger et al. Such an approach would presumably lead to a greater likelihood of that captive population evolving the capacity to respond to environmental change.
To date, however, no empirical studies on any species have addressed this possibility Frankham , though research on this topic has recently been initiated within live-gene banking programs for Atlantic salmon populations in eastern Canada P.
Still, one potential risk of this approach is that it could lead to an increase in straying to nontarget areas and thereby potentially affect other native populations. For instance, interbreeding of individuals between pink salmon populations resulted in increased straying rates to surrounding populations Bams In addition, and especially if the crosses will be carried out at a hierarchical level greater than subpopulations e.
For instance, the advantages of generating greater genetic diversity in the released individuals might be outweighed by the possible disadvantages of outbreeding depression from mixing populations reviewed in Edmands Currently, there appears to be insufficient quantitative data on salmonid reintroductions to discern whether different species or life-history types vary in their chances of being successfully reintroduced into previously occupied habitats Table 7.
However, if the ability of a salmonid species to be introduced successfully outside of its native range reflects its ability to be reintroduced into previously occupied parts of its native range, then two points merit consideration. First, anadromous populations, followed by lake migratory populations, may on average be more difficult to reintroduce than freshwater, resident populations. For instance, reviews of salmonid introductions suggest that anadromous salmonid populations do not transplant as well as freshwater species, perhaps because of their more complex requirements in having intricate life histories across multiple environments Withler ; Allendorf and Waples ; Utter Factors involved in freshwater salmonid declines might also be easier to rectify than those occurring across environments utilized by anadromous populations.
Second, species such as rainbow trout and brown trout might be easier on average to reintroduce than species such as Atlantic salmon or several other Pacific salmon species, the former having been successfully introduced in many regions throughout the world where the latter have not Quinn ; references therein; Crawford and Muir One caveat of these predictions is that they assume the potential fitness consequences of captive-rearing are uniform across species and captive-breeding programs or even life-history variants within species.
But as previously mentioned, this is likely not the case. A sensible but untested hypothesis is that captive-breeding programs elicit the greatest reductions in fitness in species or populations with the greatest life-history and habitat differences between captive and natural conditions Reisenbichler On the other hand, it appears that some supplementation programs, at least those involving juvenile releases, can achieve a measure of short-term success in terms of boosting overall numbers of fish Waples et al.
It would also seem that many salmonid populations with long histories of intense supplementation have not become extinct or severely reduced in abundance. If fitness can be reduced so much and so rapidly by domestication selection, why have not many of these populations experienced rapid declines? Thus, an unresolved enigma in evaluating the likelihood that captive breeding programs can translate into self-sustaining salmonid populations, is whether, and how, increases to population abundance N provided by captive-rearing could offset reduced fitness in the wild of captive-reared fish and their progeny.
Interestingly, there are numerous examples of the ability of salmonids to evolve rapidly in the wild over several generations Haugen and Vollestad ; Hendry et al. Certainly, then, the possibility exists that a reintroduced population based on captive-reared fish could re-adapt to the wild environment under a similar timeframe. Consider firstly a simple scenario where the original threats that led to the extirpation of a wild population have been removed and a one-time reintroduction of the captive-reared population is implemented.
Owing to inevitable domestication selection in captivity, the captive-reared population has experienced a shift away from the wild optimum in quantitative trait variation related to fitness. Thus, it is now maladapted to the wild environment. Gomulkiewicz and Holt introduced a model examining conditions under which selection might prevent extinction of the captive-bred population upon reintroduction Fig. They considered whether such a population could evolve a sufficiently positive intrinsic growth rate r at abundance N below carrying capacity K before extinction from demographic stochasticity took place.
Gomulkiewicz and Holt did not consider density-dependent effects but assumed that extinction risk was elevated below a threshold, critical population size Nc. In the context of attempting to reintroduce populations with captive-reared fish, the major implication of the model is that an initially maladapted reintroduced population with a negative growth rate could evolve a positive growth rate without going extinct, provided that: i genetic diversity was sufficiently high, ii fish were not too maladapted initially, and iii initial N was large relative to Nc to allow the reintroduced population to persist long enough for evolution to occur Fig.
Note that these conclusions are also consistent with those in previous sections relating to the importance of maintaining as high a N e as possible in captivity Frankham et al. Note also, however, that there is an inherent tension between keeping N e and genetic diversity as high as possible and reducing domestication selection in captivity, a subject treated in detail in the next section.
Potential relationships between reintroduced population abundance and extinction risk with or without evolution by natural selection, modified from Gomulkiewicz and Holt see also Kinnison and Hairston Population growth is density-independent and Nc represents a threshold abundance below which extinction risk is high.
Without evolution, or when evolution cannot achieve replacement in the absence of gene flow, reintroduced populations decline to extinction A.
Evolution is insufficient to prevent the reintroduced population from being at a high risk of extinction, but it allows the population to avoid extinction if the population persists B. Evolution is sufficient to prevent the population from being at a high risk of extinction C. Immigration and resultant gene flow allows the evolving population to avoid extinction more rapidly D than in its absence B.
Immigration and resultant gene flow increases the susceptibility of extinction to the evolving population E than in its absence. All cases assume the same reduction in wild fitness within the captive-bred population before reintroduction. Gomulkiewicz and Holt's model thus also assumed that mechanisms exist that allow for positive population growth despite reintroduction of maladapted individuals, and similarly, that at some point following the initial drop in N from K , evolutionary contributions to population growth would not be countered by density-dependent factors Gomulkiewicz and Holt ; Tufto ; Kinnison and Hairston Unfortunately, empirical assessments of these assumptions are currently very limited in salmonids.
For instance, analogous to reintroducing maladapted, captive-bred fish to a previously occupied habitat, Kinnison and Hairston and Kinnison et al. Under what conditions, then, could repeated reintroduction events increase the likelihood of successful overall reintroduction? On one hand, recurrent immigration from a maladapted, captive-reared source could demographically rescue a young, reintroduced population because the population literally never becomes extinct Holt Indeed, repeated influxes of immigrants have apparently been involved in some successful introductions or species invasions Lambrinos ; Roman and Darling On the other hand, immigrants would in general be maladapted to the local environment and resultant gene flow with the reintroduced population as it grows might constrain the effects of ongoing selection Fig.
As a rough guide based on Gomulkiewicz and Holt , the reciprocal of the time a population first reaches low densities Nc following the initial reintroduction could be used as the frequency of gene flow episodes required for population persistence due to regular immigration or introductions. In short, assessments of the relative degree to which these opposing effects might affect reintroduction success are sorely needed.
Whether single or multiple facilities are required to maintain both genetic diversity and fitness in captive breeding programs of endangered salmonids raises some important trade-offs to be factored in for biodiversity conservation.
On one hand, to avoid significant losses of genetic diversity in captivity, captive populations must be kept at sufficiently large N e to slow the rate of loss of genetic diversity due to the genetic consequences of small N e Frankham et al.
Yet, paradoxically, larger N e populations respond more readily to selection than smaller N e populations, all else being equal Robertson ; Weber and Diggins ; Allendorf and Luikart That is, a large N e facilitates adaptation by minimizing genetic drift, whereas a small N e increases genetic drift, which can hinder adaptation Crow and Kimura Consequently, while a larger N e is more advantageous than a smaller N e in the wild larger N e populations will on average be more capable of responding to environmental change than smaller N e populations , it might be disadvantageous in captivity larger N e populations may become more adapted than smaller N e populations to the captive environment.
Nevertheless, Options 4—5 must be tempered with the fact that in small N e populations, one gets more genetic drift, in addition to some selection. Thus, a key issue for accommodating fitness and genetic diversity is not only the degree to which a captive population becomes adapted to the hatchery environment, but also the degree to which the selective regimes differ between the captive and wild environment.
To throw more complexity into the different options, however, some theory Kimura and Crow ; Nei and Takahata ; see also Waples b predicts that Options 4—5 could also result in the maintenance of more overall genetic diversity and increase the overall N e compared to Options 1—3. This would only happen if no extinctions of the small populations occurred Kimura and Crow ; Nei and Takahata ; Lande ; Toro and Caballero Yet, such extinctions can arise in small captive breeding programs e.
Thus, unless there is some means to avoid these captive population extinctions altogether, the potential genetic diversity benefits of Options 4—5 might not be realized.
For salmonids, this would involve the maintenance of several small populations in captivity at one or multiple hatchery facilities, with translocations occurring only every several generations see Margan et al. To my knowledge, no empirical studies have tested whether the potential advantages of utilizing several small, isolated captive breeding populations with periodic mixture are upheld in salmonid captive breeding programs.
These authors generated replicate populations and compared the genetic diversity and reproductive fitness of populations with the following N compositions: i 50 vs. Margan et al. The N compositions involving population subdivision e. Namely, cases involving subdivided populations that were then pooled, when compared to single large populations of equivalent total size, had lower inbreeding levels, significantly higher or similar reproductive fitness, and higher levels of genetic diversity i.
There is only very limited empirical research to suggest that maintaining several small isolated populations with periodic mixing may be more effective at reducing losses of genetic diversity and fitness than maintaining a single large population. Periodic mixing might also reduce the risks associated with regular translocations e. Again, though, the tentative conclusion here is based on the assumption that no extinctions of the small populations occur in captivity.
Although Frankham recently acknowledged that such a fragmentation regime had considerable merit, he did not recommend its application, perhaps because of the limited research on the subject. I now consider some potential pros and cons of these options as they may pertain to salmonids. This might have advantages in reducing i financial costs associated with translocations, ii the stresses that translocations impose on animals depending on the life-history stage of salmonid being translocated , and iii the potential asynchrony that might arise in breeding times and embryonic developmental times by using multiple facilities that realistically vary in their thermal regimes i.
A first recommendation is that the small populations should not be so small that rapid inbreeding and loss of genetic diversity arises. A second recommendation, based on the results of Margan et al.
Consequently, decisions to adopt such a strategy would have to weigh such benefits against their added financial costs, perhaps especially for i given the kind of space required to house adult salmonids. Finally, it is difficult to gauge how long the small populations should be maintained before pooling them. Inbreeding thresholds in salmonids are poorly characterized within species Wang et al. Yet, available data indicate that the fitness effects of inbreeding might be considerable in salmonid populations at a minimum of a half-sibling inbreeding coefficient without long histories of small population size Pante et al.
As an overall cautionary approach, Margan et al. This may be unachievable in some cases unless pedigree information is available. Preceding summaries of certain sections in this review have suggested that salmonid captive-breeding programs may be unsuccessful in many cases because the root or purported causes of population decline or extirpation have not been mitigated.
This implies that technical alternatives to hatchery facilities for conserving genetic diversity and fitness will also be unsuccessful unless at least some of the root causes of salmonid extirpation are corrected. Nevertheless, such technical alternatives may have practical utility in particular circumstances for conserving biodiversity.
Since the disease likely resulted from genetic weaknesses in the Asiatic breeding stock, all the zookeepers could do was isolate the sick lions and keep them comfortable until they died. Captive breeding of Asiatic lions continues, but a black-footed ferret-style comeback seems a distant hope. Releasing animals born in captivity into their natural habitat can also be tricky.
Re-introduction can also place the wild population at risk, as it did in , when a once-captive toad brought the deadly chytrid fungus Batrachochytrium dendrobatidis to the island of Mallorca. Making sure species have suitable habitat to return to is also necessary for successful outcomes. Another challenge is artificially replicating very specific habitats, such as that of the Kihansi spray toad, a tiny amphibian whose survival requires the light mistings of a single waterfall in Tanzania.
It can be done , but figuring out when to invest in such strategies is key. The puzzle for conservation biologists is separating the ferrets from the songbirds—which species would more likely prosper from time in captivity and which should be left to fight for survival in the wild? The authors of the new paper , published in the Journal of Applied Ecology , examined the case of the great Indian bustard. Thanks to hunting and habitat destruction, this bird species consists of approximately individuals surviving on the dry plains of India and Pakistan.
See iucnredlist. Establishing captive populations is an important contribution of zoos and aquariums to the conservation of endangered species. Zoos and aquariums have limited space, however, so to maintain healthy populations, they cooperate in managing their collections as breeding populations from international to regional levels.
Perhaps the most important tools in managing these programs are studbooks, which ensure that captive populations maintain a sufficient size, demographic stability, and ample genetic diversity. All information pertinent to management of the species in question is included e. These studbooks are used to make recommendations regarding which individuals should be bred, how often, and with whom in order to minimize inbreeding and, thus, enhance the demographic and genetic security of the captive population.
Another goal of some captive breeding programs is to reintroduce animals to the wild to reestablish populations. Reintroductions can also utilize individuals from healthy wild populations, meaning individuals that are thriving in one part of the range are introduced to an area where the species was extirpated.
Reintroduction programs involve the release of individuals back into portions of their historic range, where they are monitored and either roam freely e. However, reintroduction is only feasible if survival can be assured. All rights reserved. International trade in wildlife is a multi-billion dollar industry that affects millions of plants and animals. As a result, CITES lists species in three Appendices according to the level of protection they require to avoid over-exploitation; species listed in Appendix I require the most protection and, thus, trade limitations Table 3.
Appendix Level of Protection Trade Appendix I Species threatened with extinction Permitted only in exceptional circumstances Appendix II Species might be threatened with extinction but not required Trade is controlled to ensure survival Appendix III Species are protected in at least one country Trade is controlled after a member country has indicated that assistance is needed in this capacity Table 3. Reptiles 76 spp. Amphibians 17 spp. Fish 15 spp. Plants spp.
Total spp. Table 4. Approximate number of species spp. The trade in wildlife is an international issue and, as such, cooperation between countries is required to regulate trade under CITES. However, member countries adhere to regulations voluntarily and, consequently, they must implement them. Most important, CITES does not take the place of national laws; member countries must also have their own domestic legislation in place to execute the Convention. In general, the public is unaware about the current extinction crisis.
Public awareness can be increased through education and citizen science programs. Conservation education often begins in elementary school and may be enhanced through summer camps or family vacations that are nature oriented e. Early positive experiences with nature are essential for children to gain an appreciation for wildlife and the problems species face.
In high school, this education is continued through formal science education and extra-curricular activities. Other means of increasing public awareness involve internet websites where subscribers can receive emails from conservation organizations like Defenders of Wildlife, Environmental Defense, and World Wildlife Fund.
In many cases, these organizations provide updates on the status of endangered species and promote letter writing to elected officials in requesting protection for endangered species and their habitats. Amphibians are one of the earth's most imperiled vertebrate groups, with approximately one-third of all species facing extinction Stuart et al.
In addition, the recent declines observed in relatively pristine areas, such as state, provincial, and national parks worldwide have brought to light the tremendous impact of pathogens on amphibian populations, most notably that of the amphibian-killing fungus Batrachochytrium dendrobatidis Bd. So what is being done to preserve amphibian diversity? To address the historic sources of amphibian population declines, such as overexploitation and habitat loss, national and international legislation exists to monitor the trade in amphibians and prevent further reductions in available habitat.
These species' native habitats are afforded protection at various levels of organization. The AZE has identified sites worldwide exhibiting at least one criterion for protection Table 2 , and these sites are home to hundreds of amphibian species listed by IUCN as between Vulnerable and Critically Endangered.
In addition, IUCN's Amphibian Specialist Group ASG has partnered with governmental and non-governmental organizations and individuals to create new protected areas and minimize further population declines due to habitat fragmentation and loss. In addition to designation of new protected areas, efforts of the ASG include habitat restoration, promotion of ecotourism, and extended amphibian-monitoring programs.
Figure 4: The Frosted Flatwoods Salamander Ambystoma cingulatum is endemic to the pine forests and savannahs of the southeastern United States. This species is listed as vulnerable by IUCN, and both the species and its habitat are afforded protection as a threatened species as defined by the United States Endangered Species Act and.
Despite efforts to preserve suitable habitat, biologists became increasingly aware of catastrophic population declines associated with Bd, and more urgent action became necessary when declines were detected in protected areas with minimal risks of habitat loss and overexploitation.
Batrachochytrium dendrobatidis is a parasitic fungus that disrupts the bodily processes of its amphibian hosts, resulting in lethargy and ultimately death. Although the exact origins of this pathogen are currently debated, Bd has been detected throughout the world and linked to dramatic amphibian population declines and extinctions Skerratt et al.
Due to the rapidity with which Bd invades amphibian communities, swift conservation action was deemed necessary to prevent extinctions; consequently, many institutions realized the necessity of collecting wild individuals prior to the arrival of Bd with the hopes of establishing captive populations.
Members of these organizations worldwide participate in captive amphibian husbandry and breeding programs using wild-caught individuals Figure To this day, Australia is struggling to control the spread of this invasive species. Indicator species are organisms whose presence or absence tells us about the condition of the environment. Often indicator species tell us about the levels of pollution in an area. Oxygen dissolves in water.
This comes from the oxygen in the air and that which is produced when plants photosynthesise. Without this, aquatic animals would suffocate and die. Healthy lakes and rivers have high levels of oxygen.
However, polluted waters often have low levels of oxygen. This pollution means that only certain species can survive there such as sludgeworms.
0コメント