By Olivia Quigan
Restoration is becoming an increasingly useful tool in conservation. We can now bring biodiversity back to an area that has been impaired beyond recognition by human activities, such as logging, damming, or open cast mining. Given that we are restoring more and more ecosystems around the world, does this give us leave to destroy ‘pristine’ habitats in order to exploit them to gain access to resources?
The benefits of destroying habitats in order to access resources are mostly of economic value. When cost-benefit analyses for an open cast mine are done, the only environmental outcomes that are considered are those that can be turned into a monetary value (Abelson, 2015). These are quantified as the physical impacts on the environment and how these impact health and agriculture (Abelson, 2015). This ignores the intrinsic value of unique species, as through losing them we reduce global biodiversity – a value that cannot be measured in currency (Campbell, 2014).
An argument could be made for destruction of habitats with a view to restoration, that given enough planning time, species can be saved before the habitat loss occurs. They could then be returned to the habitat during the restoration process, or found suitable homes elsewhere, that are similar to their current habitat. Translocation can be a valid restoration method, however not without its risks. This method was attempted in 2011. To allow for an open cast mine in New Zealand’s South Island, the unique and endemic Powelliphanta augusta Snails were collected and stored in shipping containers with the ultimate goal of introducing them to nearby forests. This resulted in the deaths of 800 individuals due to a technical failure of the refrigeration unit they were stored in (Vallance, 2011). This attempt was a failure, because even with the remaining snails being translocated, they are not
successfully persisting in their new environment, with death rates at new sites of up to thirty per cent (Morris, 2010). There are many other instances of failed translocations. Analyses of many reptile and amphibian translocations between 1991 and 2006 showed that up to 30 per cent of translocations failed in producing self-sustaining populations (Germano & Bishop, 2008). This rate of failure must force us to come to the conclusion that we do not yet have the knowledge to prevent extinctions in the case of a planned environmental degradation, especially when endemic species are involved, as the risk is often too high to justify needless environmental degradation.
The creation of novel landscapes is an inevitable outcome of the anthropogenic influence on the world. As we remove natural habitats, the areas that replace them won’t be the same; no matter how hard we try to restore them. A study by Lugo, Carlo and Wunderle Jr. (2011) looked at the islands of Puerto Rico and the introduced species there.
The forest cover here dropped from 100 per cent to just six per cent by the 1940s. The restoration of much of the forest has included many introduced species, both plants and animals. The resulting forest was a mixture of both, but the native plant species continue to dominate the forests, with cover of over 80 per cent. Native birds continue to be successful, and forage on both natives and introduced plants. The introduced honeybee appears to have adapted to the phenology of the native plants and is an important pollinator (Lugo, Carlo, & Wunderle Jr., 2012). This indicates that novel habitats created by restoration efforts can be sustained with introduced species, but we must continue to protect the native species to ensure lasting intrinsic value of the ecosystem.
Disturbed habitats are more likely to be susceptible to invading species. These are defined as species which “proliferate and noticeably replace native species,” (Clewell & Aronson, 2013). Invasive species with a more generalist way of life will have an advantage over native species, especially if these species have evolved into a more specialist niche (Clewell & Aronson, 2013). This is even more applicable in island habitats, where animals have evolved with limited predators. Using the land for agriculture or industry changes the scope of the ecosystem, and increases the vulnerability of it to invasions from non-native species (Vitousek, D’Antonio, Loope, Rejmanek, & Westbrooks, 1997). Human modification of environments is a major driver the invasion by non-native species. Logged forests in Thailand that were home to an invasive weed experienced an eight-fold reduction in pollinators visiting native species. The invasive beetle, Coccinella septempunctata, showed higher abundances in agricultural grasslands when compared to non-modified areas (Didham, Tylianakis, Gemmell, Rand, & Ewers, 2007). Due to the precious value of native species, the total destruction of a habitat cannot be justified as this disturbance leads to increased vulnerability to species invasions.
The complete destruction of a habitat will always be detrimental to the species living there. To destroy a habitat for monetary gain is to place a value on the uniqueness of habitats, and deem it less important than the economy. The evidence shows that we are not capable of maintaining the integrity of a habitat if we destroy it completely. Disturbed habitats are more likely to allow invasive species, which decimate native populations. Human attempts at preservation by translocation of species often fail. As we cannot guarantee the safety of our unique species, we cannot justify the destruction of any habitat; regardless of how accomplished we are becoming at restoring them.
Abelson, P. (2015). Cost–Beneﬁt Evaluation of Mining Projects. The Australian Economic Review, 442-52.
Campbell, R. (2014). Seeing through the dust: Coal in the Hunter Valley Economy. Canberra: The Australia Institute.
Clewell, A. F., & Aronson, J. (2013). Ecological Restoration – Principles, Values & Structure of an Emerging Profession (2nd ed.). Washington, D.C: Island Press.
Didham, R. K., Tylianakis, J. M., Gemmell, N. J., Rand, T. A., & Ewers, R. M. (2007). Interactive effects of habitat modification and species invasion on native species decline. Trends in Ecology and Evolution, 22(9), 489-496.
Germano, J. M., & Bishop, P. J. (2008). Suitability of Amphibians and Reptiles for Translocation. Conservation Biology, 7-15.
Lugo, A. E., Carlo, T. A., & Wunderle Jr., J. M. (2012). Natural mixing of species: Novel plant-animal communities on Caribbean Islands. Animal Conservation, 233-241.
Morris, R. (2010). An Unfortunate Experiment. Forest And Bird, 14-16.
Vallance, N. (2011, November 10). Snail fridge deaths an avoidable tragedy. Retrieved from Forest and Bird: http://www.forestandbird.org.nz/what-we-do/publications/media-release/snail-fridge-deaths-avoidable-tragedy
Vitousek, P. M., D’Antonio, C. M., Loope, L. L., Rejmanek, M., & Westbrooks, R. (1997). Introduced Species: A significant component of Human-caused Global Change. New Zealand Journal of ecology, 1-16.
By Andrea Gregor
Non-native species are known to be a strong driver of native species decline and habitat degradation (D’Antonio & Meyerson, 2002). All invasive species are non-native, yet not all non-native species are invasive (Clewell & Aronson, 2013). Non-native species have the ability to infect natives with disease, outcompete them and alter ecosystem functions (D’Antonio & Meyerson, 2002). Non-native species, however, have also been shown to enhance the process of ecological restoration by acting as an alternate food source, or increasing nutrients in soil and becoming an important part of ecosystems. I focus on non-native plant species, however non-native animal species follow similar trends, and equal research should be performed. If ecological restoration is the restoring of native landscapes, then is there any room for non-native species to be part of this process? How can we assure that non-natives used in ecological restoration will not become invasive?
The Potential Impact of Non-Native Species
An area of land that is to go through ecological restoration often has had disturbance caused by human action or environmental events (Keenleyside, Dudley, Cairns, Hall, & Stolton, 2012). According to Vilà and Weiner (2004), disturbance increases the chance of invasion by non-native species as species that have the potential to become invasive tend to be good colonisers after disturbances. As well as this, many create seed banks which allow them to endure for a long period, and make eradication difficult. With an increased risk of invasion, we get an increased risk of interspecific competition between native and non-native species. Studies conducted are unable to say that all non-native species always outcompete natives; however there is still a strong competitive effect on native species, which can cause a decline in the population of native species (Vilà & Weiner, 2004). Species compete for light, nutrients and space (Wilson & Tilman, 1993). Therefore including certain species of non-natives in restoration runs the risk that the introduction, be it accidental or not, could be detrimental to the persistence of that ecosystem through potential outcompeting and overcrowding.
If inadequate research is done, non-native species have the potential to become invasive in certain environments. Invasive species have been recognised as the second largest threat to global biodiversity after habitat fragmentation (Allendorf & Lundquist, 2003). Throughout the world, invasive species cost governments billions of dollars. Management of plants and animals listed under the Endangered Species Act cost $32-$42 million annually, in which 90% of those funds are allocated to mitigate the effects of invasive species (Wilcove & Chen 1998; D’Antonio & Meyerson 2002). In New Zealand invasive species cost $840 million each year to control, and produce a $1 billion loss in productivity (Giera & Bell, 2009). With such a large economic impact that invasive species have on New Zealand and the world, should we risk using species that have the potential to be invasive in ecological restoration?
Are All Non-Natives That Evil?
With adequate research, there is room to include non-natives in ecological restoration. Some non-native species, particularly plant species have been shown to increase the population of native species. Non-native species being used as an alternate food source for native species can lead to an increase in native population numbers due to the increased resources. For example, in the US, introduced honeysuckles are improving native bird populations (Figure 1). It is also found that seed dispersal of native plants is the highest where non-native honeysuckles are the most abundant due to dispersal by the now more populated native birds (Davis, et al., 2011). This positive effect of a non-native plant has enhanced the population of native bird species, as well as other native plants. Subsequently, removing non-native species can have negative effects to an ecosystem removal of these pine plantations will demolish the favourable , and successful eradication so far has been limited to small islands (Zavaleta, Hobbs, & Mooney, 2001). With declining native habitat, half of New Zealand’s threatened indigenous plants are found in historically rare ecosystems with localised distributions (Pawson, Ecroyd, Seaton, Shaw, & Brockerhoff, 2010). Encouraging natives to use non-native habitats as substitutes could help the continuation of species. The New Zealand large bird orchid (Chiloglottis valida) has been found within non-native Pinus nigra plantations. The microclimate under these pine trees which allow orchids to survive outside of their original habitat. Because of this reason, a small orchid reserve in this plantation has been created, while the rest of the plantation has been logged (Pawson, Ecroyd, Seaton, Shaw, & Brockerhoff, 2010). This example is one of many which show the necessity of keeping specific non-native species in order to retain native species.
Implications on Soil Nutrients
Exotic plants can alter ecosystem processes through differences in nutrient cycles. They can cause an increase, or decrease to the soil nutrients created by native species (Ehrenfeld, 2003). Negative effects of the changes in the soil microbial community can lead to an increase in the invasiveness of an ecosystem from other species (Green, O’Dowd, Abbot, Jeffery, Retallick, & Mac Nally, 2011). This has the potential to create an invasion meltdown which would undo all restoration efforts thus far and render a project useless. Changes in soil structure, such as an increase in nitrogen can encourage growth from other invasive species which outcompete natives, and shroud out the light with denser canopies, reducing the growth of native species (Allison, Nielsen, & Hughes, 2006). In Hawai’i, nitrogen fixing invasive tree Falcataria moluccana (figure 2) alters the soil structure which limits the growth of native species. Along with this, F. moluccana facilitates the invasion of another non-native species, Psidium cattleianum (also known as the strawberry guava) which outcompete natives for resources (Allison, Nielsen & Hughes, 2006). If a species such as this was used in ecological restoration without research, it has the potential to become invasive and harm the ecosystem, rather than benefit it. Changes in soil structure can also have positive effects; non-native species are able to be used positively as substitutes for slower growing natives when restoring areas with poor productivity soils which have had disturbances such as overgrazing or mining (Wong, 2003). Fast growing nitrogen fixing trees from Asia were found to grow well in degraded pastures in Puerto Rico and accelerated regeneration of native forests (D’Antonio & Meyerson, 2002). Without exotic species in circumstances like this, ecological restoration would not be able to get under way, especially if natives we are wanting to maintain struggle to establish in degraded soils. Non-natives in this case are essential to effective recovery of native sites. The differences in the nutrient cycles of non-native species and native species we want to restore will determine the impact non-natives will have on the soil composition and therefore the native species. These impacts can differ from site to site and can cause ecological restoration to fail or succeed. Research is our greatest tool to ensure we only use species that succeed, and remove species that will cause our project to fail.
With continued human movement, non-natives are becoming more and more abundant, creating many novel ecosystems (Marris, 2011). In ecological restoration, you must pick your battles; it is not possible to remove all introduced species. If a non-native has no potential of becoming invasive, and is doing no harm to an ecosystem, then leaving that species and focusing money on other areas would seem like the way forward. In some cases, I feel we should learn to embrace novel ecosystems, especially in circumstances where we are unable to return ecosystems back to their original state. Non-natives may have changed the habitat of an area to make it unsuitable for future natives, whether the non-native is present or not through changes in soil or species composition, and abundance (Norton, 2009) . According to Norton (2009), it has passed the biotic threshold, and there is no way to return the ecosystem back to its original state. If this is to have happened, and a non-native has taken over the niche of a native without affecting other species, it may be in our best interests just to embrace the change leave it there as part of a functioning ecosystem.
Non-native species have a place in ecological restoration, however we must be wary of which species we choose to include in these projects. The fact that invasive non-native species are one of the largest threats to ecological restoration means that using non-natives in these practises can lead us to walk on a fine edge between enhancing native species, and causing an invasive meltdown. Introducing non-native species seems like we are encouraging the opposite of what we are trying to achieve, however it has been shown in many cases to work. We have little room for error, therefore we must use short lived, well researched species and we must monitor them closely to ensure ecological restoration is achieved successfully. We must also acknowledge that there is always a chance of failure; a species may interact with its surrounding different than we had planned. This is a risk that is shared in all conservation and restoration projects which can be minimised, but never removed. In this essay. We must also look at the possibility of leaving non-natives that have been determined low risk to ecosystems; we can never restore every area back to its original state, but if we pick our fights correctly, we are able to nurse many native species back with the help of non-natives.
Allendorf, F. W., & Lundquist, L. L. (2003). Introduction: Population Biology, Evolution, and Control of Invasive Species. Conservation Biology Vol. 17 (1), 24-30.
Allison, S., Nielsen, C., & Hughes, R. (2006). Elevated enzyme activities in soils under the invasive nitrogen-fixing tree Falcataria moluccana. Soil Biology and Biochemistry Vol. 38(7), 1537-1544.
Clewell, A. F., & Aronson, J. (2013). Ecological Restoration – Principles, Values & Structure of an Emerging Profession (2nd ed.). Washington, D.C: Island Press.
D’Antonio, C., & Meyerson, L. (2002). Exotic Plant Species as Problems and Solutions in Ecological Restoration: A synthesis. Restoration Ecology Vol 10 (4), 703-713.
Davis, M. A., Chew, M. K., Hobbs, R. J., Lugo, A. E., Ewel, J. J., Vermeij, G. J., et al. (2011). Don’t judge species on their origins. Nature Vol 474, 153-154.
Ehrenfeld, J. G. (2003). Effects of Exotic Plant Invasions on Soil Nutrient Cycling Processes. Ecosystems Vol. 6 (6), 503-523.
Forbes, A. S., Norton, D. A., & Carswell, F. E. (2015). Underplanting degraded exotic Pinus with indigenous conifers assists forest restoration. Ecological Management and Restoration Vol 16(1), 41-49.
Giera, N., & Bell, B. (2009). Economic Costs of Pests to New Zealand. Wellington: Crown Copyright- Ministry of Agriculture and Forestry.
Green, P. T., O’Dowd, D. J., Abbot, K. L., Jeffery, M., Retallick, K., & Mac Nally, R. (2011). Invasional meltdown: Invader–invader mutualism facilitatesa secondary invasion. Ecology Vol 92(9), 1758-1768.
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Marris, E. (2011). Rambunctious Garden. New York: Bloomsbury.
Norton, D. A. (2009). Species Invasions and the Limits to Restoration: Learning from the New Zealand Experience. Science Vol 325 (5940), 569-571.
Pawson, S. M., Ecroyd, C. E., Seaton, R., Shaw, W. B., & Brockerhoff, E. G. (2010). New Zealand’s exotic plantation forests as habitats for threatened indigenous species. New Zealand Journal of Ecology Vol 34 (3), 342-355.
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by Hannes Öckerman
Previously locally extinct, the wolf has reestablished itself in Sweden in the past decades. Had this species been a bumblebee or a fungus, it would probably not have been given much attention. However, being top predator surrounded with much controversy, the wolf has caused a polarized society and an eye-opener to how we must reconcile with each other and the wild regarding restoration issues.
Hunted to extinction (Laikre et al., 2013), wolves were absent in Sweden for about a century prior to their natural recolonization in the beginning of the 1980s (Wikenros et al., 2010). They established themselves in the southwestern parts of Sweden making them geographically isolated from the Eurasian population (Ericsson and Heberlein, 2003). Descending from only five founders, individuals of the Swedish wolf population are on average more related to each other than siblings (Laikre et al., 2013). This raises deep ecological and biological concerns addressing the dangers of genetic isolation and inbreeding (Laikre, 1999; Laikre et al., 1993).
Considered a native species, the majority of the Swedish population is positive to the right of wolves to exist within the nation’s borders (Swedish Society for Nature Conservation, 2015). There is discrepancy, however, to what extent. Appointed by the Swedish government, the Predators Commission concluded in 2009 that a viable population should consist of at least 450 individuals (Swedish Society for Nature Conservation, 2013; Liljelund, 2011) in order to significantly reduce its inbreeding (Laikre et al., 2013). On the contrary, the government adopted a policy to keep numbers below 210 (Swedish Government, 2009, p. 210), possibly influenced by the interests of hunters and farmers (Franchell, 2012). Thus, Swedish authorities have permitted ‘selective culling’ of wolfs since 2010 (Carlgren, 2010) despite being a protected endangered species. The wolf hunts have been juridically controversial, potentially breaching both national and European legislation (Laikre et al., 2013).
The polarization of society
The attitude differences regarding wolf restoration can also been seen in other parts of society. As Ericsson and Heberlein (2003, p. 150) put it, “The wolf has become the symbol for the divide between urban and rural [people]”. Farmers have a more negative attitude towards wolves (Stronen et al., 2007) and studies have concluded a positive correlation between attitude and distance to a wolf territory (Ericsson and Heberlein, 2003; Karlsson and Sjöström, 2007). So while some conservationists may wish to rewild Sweden back to a 19th century baseline, with wolves present throughout the entire country, I believe this desire comes with a reservation of the wolf not showing up in one’s backyard.
Hunters have raised concerns about the wolf’s impact on game populations of moose and roe deer but it has proven to be minor in comparison to that of humans (Nicholson et al., 2014; Sand and Gervasi, 2014; Gervasi et al., 2013). Moreover, competition with other native predators such as lynx is low (Wikenros et al., 2010). A recent increase in sheep and dogs killed by wolfs is observed though (Karlsson et al., 2014) and these direct negative experiences are likely to breed more unfavorable attitudes towards the canine predator (Karlsson and Sjöström, 2007). As these attitudes probably contributed towards the authorities’ decision to hunt wolf (Franchell, 2012), one must ask: are they justified? Should farmers accept some loss of livestock to benefit an endangered species? Can it be considered a risk one takes, just like losing sheep from theft, accidents or diseases? According to Mills (1987, p. 95), “Careless husbandry is the problem, not wolves”.
As some loss of livestock and competition for game animals probably is inevitable, there are measures that could be taken towards reconciliation between farmers, hunters and conservationists, between urban and rural people. Most likely, farmers and hunters will have to adapt to wolves repopulating the country. Consequently, it is important to present alternative husbandry solutions such as existing subsidies for preventive actions (Karlsson et al., 2014), lamas to protect sheep herds (Radio Sweden, 2013) and protection vests for hunting dogs (DN, 2011). Meanwhile, conservationists should move away from historical baselines and aim for achievable goals. These could include improving the connectivity in the landscape in order to increase the gene flow and reestablish a larger metapopulation across Scandinavia, Finland and Russia (Laikre et al., 2013; Hansen et al., 2011).
As a privileged nation I believe we have an ethical responsibility in restoring the Swedish wolf. Once having disrupted the ecosystem, I argue that humans should not prevent what in many ways is a natural recolonization of a native species. Furthermore, if we were to accept systematic hunting of wolf despite being an endangered species, there is a risk of knock-on effects with other conservationist values being questioned. The whole concept of protecting endangered species could be queried.
As emphasized by Marris (2013), the restoration of a top predator is usually problematic. In Sweden it has caused a polarized society with disagreements on a sustainable wolf population size. The current situation with wolf hunts, however, hinders the mitigation efforts on inbreeding and threatens the concept of protecting endangered species. Therefore, I conclude that society and authorities need to unite behind the restoration of a genetically viable wolf population, based on scientific research and embedded in reconciliation efforts. But then again, what do I know? I live hundreds of kilometers away from the closest wolf territory…
 With the exception of single wolves occasionally wandering in from Finland or Russia.
 Protecting individuals considered genetically important
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Ericsson, G., Heberlein, T.A., 2003. Attitudes of hunters, locals, and the general public in Sweden now that the wolves are back. Biological Conservation 111, 149–159. doi:10.1016/S0006-3207(02)00258-6.
Franchell, E., 2012. EU har rätt om de svenska vargarna (EU are right about the Swedish wolfs). Aftonbladet, Stockholm.
Gervasi, V., Sand, H., Zimmermann, B., Mattisson, J., Wabakken, P., Linnell, J.D.C., 2013. Decomposing risk: Landscape structure and wolf behavior generate different predation patterns in two sympatric ungulates. Ecological Applications 23, 1722–1734. doi:10.1890/12-1615.1.
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Karlsson, J., Kjellberg, L., Månsson, J., Svensson, L., Hensel, H., Levin, M., 2014. Statistics of Wildlife Damages 2013 – Damages of inviolable game to domestic animals, dogs and crop (No. 2014-1). Institution of Ecology, Swedish University of Agricultural Sciences, Uppsala.
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Laikre, L., 1999. Conservation Genetics of Nordic Carnivores: Lessons from Zoos. Hereditas 130, 203–216. doi:10.1111/j.1601-5223.1999.00203.x.
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Laikre, L., Ryman, N., Thompson, E.A., 1993. Hereditary Blindness in a Captive Wolf (Canis lupus) Population: Frequency Reduction of a Deleterious Allele in Relation to Gene Conservation. Conservation Biology 7, 592–601.
Liljelund, L.E., 2011. Rovdjurens bevarandestatus – Delbetänkande av Rovdjursutredningen. (Predator conservation status – interim report of the Predator Investigation) (Government Public Investigation No. SOU 2011:37). Swedish Government Public Investigations, Stockholm.
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Nicholson, K.L., Milleret, C., Månsson, J., Sand, H., 2014. Testing the risk of predation hypothesis: the influence of recolonizing wolves on habitat use by moose. Oecologia 176, 69–80. doi:10.1007/s00442-014-3004-9.
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“The pathway of degradation differs from that of recovery.” – Suding and Hobbs, 2009.
Restoration ecologists have long worked to restore native habitats to their “natural state” by eradicating non-native species. Such conservation efforts need the community’s support to succeed. To obtain this support, a clear message was crafted: non-native species (including invasives) are harmful and must be eradicated. But this assertion is no longer entirely true. We now know that some non-natives are actually beneficial and should be preserved…or even introduced. Most habitats are now “novel” and will never again be “natural.” To ensure the community’s continued support for ongoing and future restoration efforts, the message must be changed. Realistic goals and practices must be conveyed convincingly to the public. Economic and cultural values should also be considered. Scientific credibility and community support are at stake.
Changing the Perspective
Global human movement of species has resulted in a breakdown of biogeographic barriers. Combined with climate change, the consequence has been novel ecosystems and species combinations (Hobbs 2006 & Meyerson 2007). Conservationists have declared war on these non-natives. The battle cry has remained unchanged: native habitats should be restored to their natural state by eradicating non-native species. This message has been forcefully and repeatedly conveyed to the public. And to some extent the message-bearers have a point. Some non-native species have had devastating effects: causing extinctions of native species, altering and destroying native habitat, and threatening animal and human health by spreading disease. Non-native species are recognised as a great threat to biodiversity. They also threaten our global environmental and economic welfare. The estimated economic impact of non-natives, including control costs, is $1.4 trillion annually, which is almost 5 percent of the global GDP (Pimentel 2001).
But it is equally clear that some non-native species are beneficial, both directly and indirectly, to native species and ecosystems. Conciliation biology, a subgroup of invasion biology, recognises just this. It promotes the concept that short- and long-term conservation management should include these interactions (Caroll 2011).
Restoration ecologists already know this, and more adaptive management plans now call for the preservation and/or introduction of non-natives. Yet, the conservation community continues to deliver a contrary message to public. Let’s take a look at some essential restoration practices that are currently in use.
Take for Example…
Taxon substitutes are non-natives that support restoration efforts by filling ecological niches left by extinct or fragmented populations. One example is the non-native Aldabra giant tortoise (Aldabrachelys gigantea) which was introduced to the surrounding islands of Mauritius. These animals were intended to replace extinct native large-bodied vertebrates that served as generalists and seed dispersers. The tortoises’ introduction has succeeded in maintaining ecosystem heterogeneity and native biodiversity. As a result, the giant tortoise is being considered for other similarly degraded insular ecosystems around the world (Griffiths & Harris 2010, Hansen 2010).
The introduced African honeybee (Apis mellifera scutellata) had an unexpected positive effect on Dinizia excelsa (canopy tree) in Amazonian pastures (Figure 2). Due to human-induced habitat loss and fragmentation, D. excelsa was expected to experience a decline in population resulting from the disruption in mutualism by native pollinators. Instead, the honeybee replaced the native pollinators, enabling the D. excelsa to not only thrive in fragmented areas but to have a higher vigour and genetic diversity than the same trees in a contiguous forest (Dick 2001). Once considered a pest, this non-native has become an invaluable part of the management strategy, ensuring the preservation of this native habitat and species.
And lest we forget about biocontrol…
Biocontrol is another restoration practice which introduces non-native species to control other non-natives. A prime example of biocontrol is the introduction of the non-native Tanzania Eurytoma erythrinae to control a non-native gall wasp (Quadrastichus erythrinae). The wasp was introduced to Hawaii and soon attacked a native Erythrina species, leading to massive population declines (Rayna 2013). The biocontrol successfully suppressed some of the wasp infestation, allowing the Erythrina population to partially recover. This non-native biocontrol agent should be preserved. It has become part of its adopted environment and will protect the native Erythrina from extinction.
Changing the Message
Introducing and/or preserving non-natives are essential to restoring and protecting native habitats. But how can conservationists reconcile these practices with the repeated message that all non-natives should be eradicated? They can’t. And worse, they will likely have trouble promoting these new practices to a public made sceptical by the conflicting messages. The public may even lose confidence in the scientific community, seeing the changing message as an admission of faulty science. (“Hey Alexander, did you hear that the world really isn’t flat after all?!”) And if they were wrong before, perhaps they are wrong now. The public may oppose these new practices or simply throw their hands up in resignation, not knowing what to believe.
Yes, the message must change, but it must be done in a thoughtful way, considering ongoing and future management practices including non-natives. In other words, we have to learn from our mistakes.
In the excitement of a dawning movement and the rush to convince the public, scientists sometimes put little thought into crafting the message. For example, environmentalists used to warn against “global warming”. Scientists subsequently changed the message to the broader term, “climate change” after determining that other environmental changes posed more significant impacts on humans than increasing surface temperatures. The changing message fuelled scepticism about the legitimacy of the underlying science, eroding public support.
In the conservation context, non-native species were once referred to as “alien” species. That term, which conjured up visions of space invaders, was subsequently discouraged. Similarly, “invasive” species suggests an unwelcome visitor. “Non-native” connotes a species that doesn’t belong. These terms implicitly suggest that the subject species is harmful and intrusive. The negative connotation of these terms supports the message that non-native (alien, invasive, etc.) species should be eradicated. Predictably, this will make it even harder to garner public support when the message is changed to call for the preservation and/or introduction of “non-native” or “invasive” species.
Perhaps then it is time to retire the terms, “native” and “non-native.” In “Who’s Invading What,” the author suggests that the non-native/native dichotomy may eventually give way to “dominant”/“non-dominant” species. The spread of a dominant species may promote a decline in species diversity (Larson 2007). Whether the dominant species is “native” or “non-native” would seem to be of little importance (Houlahan and Findlay 2004; White 2006; Meiners 2007). More important is the reduction in ecological functioning and the diminished landscape diversity.
The New Message
So, the message should change. But what should it become? Perhaps something like this: Although there are legitimate reasons to eradicate some non-natives, restoring a native habitat to its natural state should not top the list. Restoring a habitat to its natural state is a largely unattainable goal – a financial “luxury” affordable by only a handful of communities. For the rest, restoration efforts should be designed to restore merely some of the habitat’s original functional attributes. This could be watershed preservation, providing habitat for natives, and economic recovery or return (Ewel and Putz 2004). The use of non-natives can play an integral part in these efforts. But even partial restoration efforts are not inexpensive (Mitsch and Gosselink 2000). Non-natives are often the most cost-effective option (D’Antonio and Meyerson 2002). Reducing the restoration price tag may engender social acceptance.
The new message should inform the public about the unavoidable development of “novel” ecosystems which are normal responses to environmental changes and disturbances. Alterations in climate change and land use affect species distributions and the environment. These alterations modify the composition and/or function of ecosystems. If you think about it, all ecosystems were novel at some point in time (Root 2006 and Harris 2006).
The new message should also consider the cultural uses and socio-economic value of non-native species. Restoration ecologists should be mindful of the cultural and political sensitivities of local communities. The success or failure of any particular restoration project can easily turn on social acceptance or rejection. The public’s support may be a prerequisite to obtaining the funds, labor, and regulatory approval necessary to complete the project. Resources should be carefully allocated to conservation efforts that yield more desirable results.
The new message should be broad enough to encompass ongoing as well as future practices. New research, co-evolutionary responses, and environmental resilience should be considered.
Now is the Time
It is time to modify efforts to restore native habitats to their “natural” state. Long-term adaptive management plans must include appropriate non-natives to promote the efficient use of resources. Most habitats are now novel and dependent on non-native species. There will continue to be a subgroup of non-native species that cause environmental, economic, and social damage. However, other non-natives will adapt and contribute to evolving ecosystems (Schlaepfer 2011). Messaging is key to obtaining critical public support. Evolving science and conservation practices may require future changes to the messaging. Today’s message must be flexible enough to accommodate these future changes. Scientific credibility and community support depend on a coherent message. We must always look forward while working to preserve the past.
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Paul G. Roman is currently enroled in the Masters of Conservation Biology programme. This unique programme is offered jointly by Victoria University of Wellington, located in New Zealand’s capital city, and The University of New South Wales in Sydney, Australia. Mr. Roman graduated with a Bachelor of Science in Biology from the University of Hawaii in 2010. After graduation, he worked in conservation in Hawaii for 3 years as a field technician for both the Ko’olau Mountains Watershed Partnership and the Wai’anae Mountains Watershed Partnership.
Friend or foe? The controversial status of native predators in New Zealand restoration projects using weka as a case study species – Asher CookPosted: May 4, 2014
Introduced predators have had a catastrophic impact on New Zealand’s unique flora and fauna (King, 1984; O’Donnell, 1996; Holdaway, 1999). Generally, given their non-native status, the control or eradication of introduced predators is a logical procedure that results in clear conservation benefits for native biodiversity (Moorhouse et al. 2003; Whitehead et al. 2008). However, an important but often overlooked issue arises when predation pressure is exerted by native species. In this case, the distinction between predator control and conservation gain is blurred and is exacerbated when the predator is, itself, a threatened species. This paradoxical situation raises an important question – are New Zealand’s native predators friend or foe? This essay will (1) focus on weka (Gallirallus australis) as a real-life example of a native New Zealand predator, (2) present the arguments for and against their inclusion in restoration projects and (3) provide a generalised decision-making framework designed to help conservation practitioners who are considering the reintroduction of a native predator species.
New Zealand’s native predators
New Zealand has a number of native species that are at least part-time predators of native vertebrate fauna – avian examples include swamp harrier, pukeko, morepork, New Zealand Falcon and weka (van Winkel & Ji, 2012; Dey & Jamieson, 2013). They consume a wide range of prey including birds, lizards and bats, and several of these predator species have been controlled to protect rare native species (Seaton & Hyde, 2013). Both weka and New Zealand falcon are threatened with extinction (Miskelly et al. 2008).
Why can native predators pose problems in New Zealand?
Generally in natural predator-prey scenarios the prey species are robust enough to withstand predation from native predators (Salo et al. 2007). Yet, many of New Zealand’s surviving endemic species have small and fragmented populations in which even relatively low rates of predation by native species may cause population decline (especially when coupled with predation by introduced species). This means that in some scenarios native predators pose a significant threat to native biodiversity. Pukeko, for example, are controlled in pateke/brown teal breeding areas due to the threat they pose at high densities to eggs and ducklings (O’Connor et al. 2007; Dey & Jamieson, 2013).
The weka is an iconic large flightless endemic rail (figure 1). Originally found throughout mainland New Zealand, they are now extinct over large tracts of their former range due to a combination of predation (particularly by mustelids), drought susceptibility and habitat loss (Beauchamp, 1997; Miskelly & Beauchamp, 2004). Three of the four subspecies are listed as threatened according to the New Zealand Threat Classification System (Molloy et al. 2002) with the northern and Stewart Island weka listed as ‘nationally vulnerable’ and the western weka as ‘declining’ (Miskelly, 2008). Though invertebrates and fruit constitute most of their diet they also opportunistically prey on lizards, snails, eggs and juvenile ground nesting birds (Harper, 2006).
Weka have the potential for both negative and positive spin-offs for native biodiversity. Therefore they provide an important case study to compare the advantages and disadvantages of including a native predator in a restoration project.
Is it friend…?
There are a number of reasons that support the inclusion of weka within restoration projects. Conservation benefits include increased dispersal of large-fruited plants such as hinau, tawa and taraire (Beauchamp& Butler, 1999). This is especially important because most other species capable of dispersing large seed are now either extinct or absent across large areas of the country (Clout, 1989). In addition, weka also prey upon mammalian pests (namely rats and mice) so can provide a natural form of pest control within mainland sanctuaries – this is particularly significant in unfenced sites where total eradication of introduced mammals is currently infeasible (Saunders & Norton, 2001).
Most of the high-impact weka scenarios have occurred on seabird-dominated offshore islands more than 1 km from the mainland where weka do not naturally occur (Miskelly & Beauchamp, 2004). The grounds for eradication from off-shore islands (where weka often reach high densities) should not necessarily be applied to mainland sanctuaries which are generally within their natural range. In ‘natural’ mainland populations it is likely that other native vertebrate species could cope with weka predation (unless prey populations are particularly small or vulnerable) (Salo et al. 2007). Weka also hold strong cultural significance to some iwi and their availability for sustainable harvest remains an important issue (Beauchamp & Butler,1999).
Weka are prone to rapid population decline and as a result they are now more threatened than many of the species that restoration projects are designed to protect (Miskelly, 2008). North island weka populations in the Gisborne region plummeted during the mid-1980s through to the early 1990s and disappeared from a majority of their former range (Beauchamp et al. 1998). Similar sharp declines were also observed in a Northland population over a similar period when the local population declined from approximately 400 birds to just three individuals in only eight years (Beauchamp, 1997). Many of the large, stable weka populations now occur on offshore islands (Chathams, Kawau, Kapiti) where they have been introduced and act as an important insurance policy to their fragile mainland counterparts.
Their threatened status and susceptibility to sudden population decline suggests that at least limited inclusion in restoration projects is essential to their long-term survival.
Or is it foe…?
Arguments against their inclusion in restoration projects focus mainly on the negative impact they can have on other native vertebrates. Weka have a documented history of predation on a wide range of native species. These include sooty shearwater chicks on the southern Titi Islands (Harper, 2006), petrels on Macquarie Island (Brothers, 1984), lizards on islands free of introduced mammals (Hitchmough, 1998), saddleback (Lovegrove, 1992; Roberts, 1994), North Island kaka, little spotted kiwi (Miskelly & Beauchamp, 2004), snipe (Miskelly, 1987) and Fiordland-crested penguins (St. Clair & St. Clair, 1992). Furthermore, they are thought to have contributed to the extinction of the Macquarie island parakeet (Taylor, 1979). As a result, weka have been removed from at least nine island restoration projects (figure 2) and have been excluded from the reintroduction lists of many mainland projects (Miskelly & Beauchamp, 2004). However, in most examples it remains unclear whether weka predation rates are high enough to induce population decline. Further quantitative research is needed to more accurately determine their impact and would bring more scientific rigour to the ongoing debate.
Their potential for negative impacts on such a wide range of native species suggests that ubiquitous inclusion in restoration projects is neither logical nor feasible.
Posing the important questions
There are a number of important questions that conservation practitioners face when considering their stance on weka – these questions can be applied to other similar situations involving native predator species. The first clear distinction to consider is whether the predator species is already present within the boundaries of the restoration project. Logically, if it is already present then decision making will focus on whether or not to remove the predator. Conversely, if it is absent, focus will be placed on the whether to undertake a reintroduction.
Listed below (figure 3) are some important questions to contemplate when considering the reintroduction of a native predator:
In the case of question (1) if the extinction threat (refer to Miskelly, 2008) of the potential prey species are higher than the extinction threat of the predator, a reintroduction effort should not be considered given that even low rates of additive predation can exert severe population pressure on small populations (O’Donnell, 1996). In this situation other reintroduction sites with less threatened prey species should be considered.
In cases where the extinction threat of the prey species is low but concern remains over the impact of the reintroduced predator, population modelling (incorporating the expected predation rate) can give some idea of the likely scale of impact. In this case, question (2) should be considered because empirical site-specific population data is required for accurate modelling and informative predictions.
Before practitioners proceed with a reintroduction, questions (3) and (4) should also be considered. Evidence of coexistence in similar situations provides strong evidence that a reintroduction could be successful for both predator and prey. In circumstances where there are no examples of coexistence then reintroduction efforts should be considered with extreme caution. Question (4) is also an inquiry of fundamental importance given that predator impacts are usually intensified outside of their natural range (Salo et al. 2007). As mentioned earlier, most high-impact weka scenarios have occurred on offshore islands outside of their natural range (Miskelly & Beauchamp, 2004).
It is well-documented that introduced mammalian predators have had a detrimental impact on New Zealand’s biodiversity (Holdaway, 1999; Croll, 2005). Therefore, the control of predators is generally a logical procedure that leads to clear benefits for native biodiversity. However, when predation pressure is exerted by native species the distinction between predator control and conservation gain is made unclear. In this scenario there is no easy answer.
Sometimes native predators are our friends. Sometimes they are foe.
The example of weka in New Zealand emphasises the need for flexibility in our approach toward native predators in restoration projects.
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 This list of questions should be used in conjunction with those asked in regular reintroductions. See Seddon et al. 2007 (http://onlinelibrary.wiley.com/doi/10.1111/j.1523-1739.2006.00627.x/full) and Armstrong et al. 2008 (http://ac.els-cdn.com/S0169534707003345/1-s2.0-S0169534707003345-main.pdf?_tid=7ee08b5c-bc6c-11e3-a7b0-00000aab0f27&acdnat=1396666172_79fb8b9cdd14260d86ca36bb2f595a7f) for more background information.