tag:theconversation.com,2011:/global/topics/invasive-species-series-39958/articlesInvasive species series – The Conversation2017-09-11T19:59:23Ztag:theconversation.com,2011:article/821812017-09-11T19:59:23Z2017-09-11T19:59:23ZInvasive plants have a much bigger impact than we imagine<figure><img src="https://images.theconversation.com/files/185507/original/file-20170911-1336-1ovqssw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Invasive pine trees in the Western Cape have affected lizards causing their numbers to drop significantly.</span> <span class="attribution"><span class="source">Author supplied</span></span></figcaption></figure><p><em>This article is the fifth in a <a href="https://theconversation.com/africa/topics/invasive-species-series-39958">series</a> The Conversation Africa is running on invasive species.</em></p>
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<p>Most people would agree that <a href="http://www.iucngisd.org/gisd/">invasive plants</a> are unwanted. Invasive plants are plants that are intentionally or accidentally introduced by humans into areas outside of their natural habitat. These species can spread rapidly with negative consequences for native species. </p>
<p>Invasive plant species have an impact on the diversity of local species, they affect water availability and damage the quality of soil nutrients. Once an alien plant has invaded a habitat, it changes the conditions of that environment. It does so by changing the light, solar radiation and temperature levels in the invaded patches. The quality and availability of food, shelter, nest sites, basking sites and perches are changed for a number of animals. </p>
<p>They can also inflict big changes on native vegetation, altering the frequency of fires, nutrient cycling, water availability and soil erosion. For example, pine trees in the Western Cape Province of South Africa <a href="https://link.springer.com/article/10.1007/s00442-016-3726-y">have spread beyond forestry plantations and invaded</a> native fynbos habitat. In these invaded landscapes, the temperatures available to lizards for functioning optimally are generally cooler and the number of lizard species greatly reduced. </p>
<p>In a few cases, some benefits of alien plants have been reported. For example, they can provide fire wood for local communities or add resources for animal species. But these benefits typically do not surpass the negative effects. Invasive plants have an impact on native species through complex interactions and processes. Unless these factors are properly understood, it is difficult to predict what sort of impact invasive plants will have. </p>
<p>How much is known about these processes in South African habitats, where invasive alien plants are a key concern? To find the answer, we read all the studies on the impact of alien plant on animals that we could find from South Africa and presented these findings in <a href="http://www.abcjournal.org/index.php/ABC/article/view/2166">a recent study</a>. We focused on ectothermic animals (reptiles, amphibians and invertebrates), known as “cold blooded”. They <a href="http://www.nhc.ed.ac.uk/index.php?page=24.134.137.139">require heat exchange</a> from the environment to function, grow and reproduce. These animals typically move smaller distances than mammals or birds, which increase their vulnerability to alien plant invasions. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/185510/original/file-20170911-1327-wvoh0d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/185510/original/file-20170911-1327-wvoh0d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/185510/original/file-20170911-1327-wvoh0d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/185510/original/file-20170911-1327-wvoh0d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/185510/original/file-20170911-1327-wvoh0d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/185510/original/file-20170911-1327-wvoh0d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/185510/original/file-20170911-1327-wvoh0d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/185510/original/file-20170911-1327-wvoh0d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Alien vegetation has shaded Nile crocodile nests which are much cooler than normal sunny nests which female crocodiles prefer.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
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</figure>
<h2>A South African perspective</h2>
<p>Habitats that have invasive plants in South Africa have a poorer diversity of animal species than whole native habitats. There are multiple reasons for this poorer animal diversity, like reduced availability of food resources or thermal conditions that are essential for animal survival. These effects can also occur in tandem or accumulate in time and space. This echoes similar findings in other regions <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1461-0248.2011.01628.x/abstract">of the world</a>. There are however many gaps. </p>
<p>Existing studies focus on a few areas of South Africa and look at a small number of alien plants including Acacia, Hakea and Pinus species. Most studies examine the impact of alien plants on invertebrates, especially insects, but we have little data of how they impact reptiles and amphibians. South Africa is unique in its numbers of endemic <a href="http://www.tandfonline.com/doi/abs/10.1080/02541858.1995.11448377">tortoises</a>, lizards, <a href="http://sarca.adu.org.za/index.php">snakes</a> and <a href="http://sarca.adu.org.za/safap/index.php">amphibians</a>. But there are not many <a href="http://link.springer.com/article/10.1007/s00442-016-3726-y">studies</a> that address these species.</p>
<p>A nice example of how alien plants impact native animals comes from a <a href="http://www.sciencedirect.com/science/article/pii/S0006320700001774">study</a> in Lake St. Lucia, on the eastern part of South Africa. Alien vegetation has shaded Nile crocodile nests. Since being invaded, nests are much cooler than normal sunny nests which female crocodiles prefer. Temperature dictates the sex of embryos in reptiles, so this finding implies that development of eggs under these conditions will result in more females. These nest temperature changes could therefore affect the population’s demographics in the long-term and alter higher levels of organisation, like communities and species. So, invasive plant species might affect the environment in more ways than we can imagine.</p>
<p>The Nile crocodile study and <a href="http://www.sciencedirect.com/science/article/pii/S000632071200328X">a few other studies</a> in South Africa are the exception rather than the rule. Most attention to date has gone into comparing numbers of species or individuals between native and invaded areas rather than investigating how these changes take place. Most authors report about the potential impact invasive plants have but very few actually test potential causes of these impacts. </p>
<p>This gap is possibly because of the difficulty to experimentally test the ways these impacts develop or record data in the long-term. For example, monitoring and collecting data on native species in the long run would enable comparing processes before and after an alien plant invasion has taken place. </p>
<h2>Where to now?</h2>
<p>Without understanding what causes the potential impact these aliens plants can have, we cannot project the impact of introduced alien species into new regions or into the future. Management practices need to be shaped by the knowledge of these causes. <a href="http://www.ladybird-survey.org/">Scientists and citizens</a> can keep a fairly good record of newly introduced invasive plant species and the spread of established ones. </p>
<p>It becomes a huge challenge to keep comprehensive records of the ways alien plants affect local plants and animals. This difficulty is mostly because <a href="http://www.sciencedirect.com/science/article/pii/S0169534712001747">these processes</a> are often multiple and can change across time and geographic regions. </p>
<p>So, we face a challenge to capture these processes. But in an era of <a href="http://www.nature.com/nature/journal/v498/n7453/full/498255a.html">big data</a>, <a href="http://www.sciencemag.org/careers/2014/06/give-and-it-will-be-given-you">data sharing</a>, cross-country collaborations and <a href="http://science.sciencemag.org/content/343/6178/1436">public participation</a>, it is a task that can be handled.</p><img src="https://counter.theconversation.com/content/82181/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Susana Clusella-Trullas receives funding from National Research Foundation, South Africa. </span></em></p><p class="fine-print"><em><span>Raquel A Garcia receives funding from the Centre of Excellence for Invasion Biology (CIB). </span></em></p>Invasive plants have an impact on native species and unless these factors are properly understood, it is difficult to predict what sort of impact invasive plants will have.Susana Clusella-Trullas, physiological ecologist at the C·I·B, Stellenbosch UniversityRaquel A Garcia, Postdoctoral fellow at the CIB, Stellnbosch University, Stellenbosch UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/809992017-07-27T03:04:16Z2017-07-27T03:04:16ZLifting the lid on how frogs find their way to foreign lands<figure><img src="https://images.theconversation.com/files/179604/original/file-20170725-21564-5g3y7b.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/berniedup/5984078857/in/photolist-bujaGn-rwZTKA-a7MYap-a7QRxN-aWXAd2-7QnNdT-rhJtau-rzgVDv-rzgNKF-ru4ka5">Bernard DUPONT/Flickr</a></span></figcaption></figure><p><em>This article is the fourth in a <a href="https://theconversation.com/africa/topics/invasive-species-series-39958">series</a>. The Conversation Africa is running on invasive species.</em></p>
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<p>A bunch of bananas seems like an unlikely mode of transport for frogs to invade the world. But it’s not far-fetched. In South Africa bananas are moved extensively around the country and are a significant pathway for the movement of frogs from one area to another. </p>
<p>But bananas aren’t the only fruit or vegetable that enables frogs to move around. </p>
<p>Take South Africa’s <a href="http://www.abcjournal.org/index.php/ABC/article/viewFile/2117/2129">painted reed frog</a> (<em>Hyperolius marmoratus</em>) which originally came from the southern Cape. Aside from hopping onto a piece of fruit, it used caravans and nursery plants to expand the areas it lives in. The species is now found all across the Western Cape Province. </p>
<p>Not all invasive frogs come from the same country. Some make it from one continent to another, such as the cane toad which is now highly invasive in Australia.</p>
<p>Identifying how species are moved from one place to another involves studying the pathways provided by human trade and travel, and determining how they can be controlled to prevent new introductions that might lead to invasions. </p>
<p>We set out to <a href="http://www.abcjournal.org/index.php/ABC/article/viewFile/2117/2129">research</a> how southern Africa’s frogs move around the region. Invasive frogs can have a major impact on the environment. They can bring diseases or parasites and can poison other animals <a href="http://john.measey.com/media/04b7de1b-5634-4e72-b685-7a6f05c92f55/xqRrVw/PDFs/Rebelo%20Measey_2017.pdf">that try to eat them.</a></p>
<p>By studying invasions in southern Africa we have been able to understand how frogs might invade the region in the future. This opens the door to designing policies that can ensure those that cause harm can be managed.</p>
<h2>Invasion pathways</h2>
<p>The movement of frogs on plants, vegetables, and fruit is known as jump dispersal. We found that there are many different kinds of invasion pathways. These include:</p>
<ul>
<li><p>leading-edge dispersal: animals colonise neighbouring water bodies close to the edge of their range;</p></li>
<li><p>corridor dispersal: species move along a convenient river or valley;</p></li>
<li><p>extreme long-distance dispersal: when frogs creep into a shipping container for example; and</p></li>
<li><p>cultivation dispersal: where animals that were purposefully bred for export to a new region, then escape and multiply. </p></li>
</ul>
<h2>Bad invasions</h2>
<p>A number of frog species that were introduced to new regions for specific purposes and then escaped have become notorious because of the damage they’ve caused. </p>
<p>The Cane Toad was introduced to <a href="http://onlinelibrary.wiley.com/doi/10.1111/j.1095-8312.1981.tb01645.x/full">more than 40 countries</a> in the 1930s as a biological control agent against a boring beetle in sugar cane. The toads were ineffective at beetle control, but they thrived in most areas of their invasive range, especially Australia. Today, predators that eat them <a href="http://rspb.royalsocietypublishing.org/content/273/1593/1545.short">suffer the effects of toad toxins.</a></p>
<p>North American Bullfrogs, initially grown for <a href="http://eattheinvaders.org/bullfrog/">culinary purposes</a> were exported to other countries, particularly Europe where frog legs are considered a delicacy. They are large and predatory and <a href="https://peerj.com/articles/1204/">consume other frogs in great numbers</a> making it difficult for other species to share their habitats.</p>
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<a href="https://images.theconversation.com/files/178671/original/file-20170718-2912-fc623s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/178671/original/file-20170718-2912-fc623s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/178671/original/file-20170718-2912-fc623s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/178671/original/file-20170718-2912-fc623s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/178671/original/file-20170718-2912-fc623s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/178671/original/file-20170718-2912-fc623s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=425&fit=crop&dpr=1 754w, https://images.theconversation.com/files/178671/original/file-20170718-2912-fc623s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=425&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/178671/original/file-20170718-2912-fc623s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=425&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">North American Bullfrogs, were initially grown for culinary purposes.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
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</figure>
<p>The African clawed frog originated in South Africa but was transported across the western world, in the first instance, <a href="http://www.ijdb.ehu.es/web/paper.php?doi=10761846">for use as pregnancy tests during the 1930s</a>. Pregnancy was confirmed by an injection of urine from the patient leading to spawning in lab animals, which were in common use up to the late 1960s. Later they were used as model animals in <a href="http://www.tandfonline.com/doi/full/10.1080/0035919X.2016.1158747">science classes and as pets</a>. Some escaped or were released. They are now common in parts of North America, <a href="https://www.researchgate.net/publication/264850290_An_invasive_population_of_Xenopus_laevis_in_Italy">South America, Asia and Europe</a>. </p>
<h2>How do toads get inside shipping containers?</h2>
<p>Many species that become invasive are already anthropophilic – common around human habitations and even industrial areas. Large toads in particular are attracted to strong lighting where insects also congregate. As the light of day arrives, they need to find somewhere dark to hide, and this could be an open container.</p>
<p>Toads are able to withstand dryness and starvation for extended periods, perhaps as long as a month. These toads may simply stay to their hiding places and wait for better times. Once the cargo has been unloaded, they emerge into a new ecosystem.</p>
<p>Once back on land, they need to find a mate and a breeding site. Most urban and peri-urban areas are riddled with suitable breeding habitats like garden ponds and other bodies of water like farm dams which have facilitated <a href="http://onlinelibrary.wiley.com/doi/10.1111/aec.12022/full">“leading-edge dispersal” in the painted reed frog</a>. </p>
<p>The guttural toad has colonised artificial garden ponds, promoting “jump dispersal” to <a href="http://www.abcjournal.org/index.php/ABC/article/viewFile/2117/2129">a growing area of peri-urban Cape Town</a>. </p>
<h2>Wise up</h2>
<p>The movement of goods around the world on ships is growing. These include <a href="http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0173340">containers bound for Africa</a>. No doubt, some of this cargo will contain potential invaders, and we need to be sure that we have <a href="https://www.environment.gov.za/sites/default/files/docs/publications/biosecurity_southafrica.pdf">biosecurity</a> measures in place to manage them.</p>
<p>Once-upon-a-time the frog in a bunch of bananas on a supermarket shelf was an oddity to be admired. But we need to wise up. They could represent pathways for invasions.</p><img src="https://counter.theconversation.com/content/80999/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Measey receives funding from the DST-NRF Centre of Excellence for Invasion Biology, South Africa's National Research Foundation and Stellenbosch University.. </span></em></p><p class="fine-print"><em><span>Sarah Davies receives funding from the DST-NRF Centre of Excellence for Invasion Biology and Stellenbosch University. </span></em></p>Invasive frogs can have a major impact on the environment. Some move continents by human trade or travel. But determining how to control them can lead to policies that limit their spread and effects.John Measey, Senior Researcher at the CIB based in the Department of Botany and Zoology, Stellenbosch UniversitySarah Davies, Deputy Director: Centre of excellence for invasion biology, Stellenbosch UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/798682017-07-10T15:24:04Z2017-07-10T15:24:04ZSouth Africa should sort out the bad from the really bad on its invasive species list<figure><img src="https://images.theconversation.com/files/177520/original/file-20170710-29699-vqh4hb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Managing trout is a contentious issue with conflicting views about whether they pose a risk, or are beneficial.</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p><em>This article is the third in a <a href="https://theconversation.com/topics/invasive-species-africa-40566">series</a> The Conversation Africa is running on invasive species.</em></p>
<p>Alien species have been introduced to Africa for a variety of reasons. They provide food, raw materials for industry, ornamental plants, recreation in the form of sport fishing, hunting and pets. Some that are highly valued have been moved around widely. And in some areas they now form prominent components of societies and ecosystems like the domestic cat for example.</p>
<p>Many alien species bring considerable benefits. But some have become invasive, causing a loss of biodiversity, changes to ecosystems, economic losses and, in some cases, even affecting people’s health.</p>
<p>The shrub <a href="http://www.arc.agric.za/arc-ppri/Pages/Mesquite-Prosopis.aspx"><em>Prosopis</em></a> or mesquite is an example. It was introduced to South Africa to provide fodder, firewood and shade in arid parts of the country. But it’s also a <a href="http://www.arc.agric.za/arc-ppri/Pages/Mesquite-Prosopis.aspx">major water user</a>. And two trout species (<em>S. trutta</em> and <em>O. mykiss</em>) are used for recreational angling and commercial aquaculture. But they’ve also been implicated in having a negative effect on the environment. </p>
<p>Managing invasive species is therefore critical. In South Africa the movement and use of 552 listed invasive species are managed under the <a href="http://www.gov.za/documents/national-environmental-management-biodiversity-act-0">Biodiversity Act</a> and regulations attached to it. But not all the species on the list are equally harmful. Several may in fact be relatively harmless. </p>
<p>All the listed species under these regulations require management. Given that the capacity is limited, regulations should arguably focus on priority species because not all are necessarily harmful to the extent that would justify spending large amounts of time and effort on keeping them under control. </p>
<p>The question then is: are there some species that could be removed from the list? In our recent <a href="https://doi.org/10.4102/abc.v47i2.2160">study</a> we set out to answer this question by classifying species as inconsequential, beneficial, destructive or conflict generating species. This was done by assessing the relative degree of benefit they brought and their negative effects. </p>
<h2>Beneficial and harmful species</h2>
<p>The classification was done by using a simple scoring system. It had two categories for the negatives (ecological and socio-economic) and two for the benefits (economic and intrinsic).</p>
<ol>
<li><p>Inconsequential species: these make up 55% of the species listed under the act and in the regulations. They were associated with relatively low costs and low benefits to society. Species in this group had limited distribution or no known impact and were largely introduced as ornamentals or pets. Some examples include the eastern grey squirrel (<em>Sciurus carolinensis</em>), European perch (<em>Perca fluviatilis</em>), and the Père David’s Deer (<em>Elaphurus davidianus</em>).</p></li>
<li><p>Destructive species: these make up 29% of the list. They don’t bring substantial benefits to society or the environment, but they have a highly negative impact. Many were introduced accidentally and are regarded largely as pests and weeds. Examples include invasive rodents like the black rat (<em>Rattus rattus</em>) which causes damage to infrastructure and <a href="http://dx.doi.org/10.1080/10408410902989837">transmission of zoonotic diseases</a> and pitch canker (<em>Fusarium circinatum</em>) a growing threat to <a href="https://link.springer.com/article/10.1071/AP08036">pine plantations and forests worldwide</a>. </p></li>
</ol>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/177521/original/file-20170710-4369-150l1v6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/177521/original/file-20170710-4369-150l1v6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/177521/original/file-20170710-4369-150l1v6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/177521/original/file-20170710-4369-150l1v6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/177521/original/file-20170710-4369-150l1v6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/177521/original/file-20170710-4369-150l1v6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/177521/original/file-20170710-4369-150l1v6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/177521/original/file-20170710-4369-150l1v6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The jacaranda is an iconic tree species in the city of Pretoria where it’s regarded as part of the identity.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<ol>
<li><p>Beneficial species: they make up 10% of the list and have clear social or environmental benefits. For example the jacaranda (<em>Jacaranda mimosifolia</em>) is an iconic tree species in the city of Pretoria where the species is regarded as part of the identity and <a href="http://www.stratek.co.za/.%5Carchive%5Cronniekasrils.html">“sense of place” of the city</a>. Active management is not necessary or should only be done in particular cases. </p></li>
<li><p>Conflict-generating organisms: these can be either beneficial or destructive, depending on one’s perspective or what value is placed on them. They make up only 6% of the list. There’s huge disagreement about whether these species should be controlled, or how they should be controlled. Examples include woody plants introduced for forestry, erosion control, sand dune stabilisation, agriculture and as ornamentals. Acacias and pines <a href="https://link.springer.com/article/10.1007/s10530-013-0615-8">are examples</a>. Animal examples include species like the Himalayan tahr which was introduced to the Table Mountain National Park. The goat has been the focus of <a href="https://doi.org/10.1016/j.landurbplan.2016.03.010">eradication attempts</a>, despite strong opposition. It also includes species introduced for aquaculture like maroon and brown trout. Managing trout has been highly contentious with conflicting views about whether they pose a risk, or deliver a benefit. This has led to them being listed and delisted. The trout fraternity refuse to acknowledge that trout are invasive species and highlight the lack of scientific evidence of the risks <a href="http://www.farmersweekly.co.za/opinion/by-invitation/is-this-the-end-of-the-line-for-freshwater-fishing/">they pose</a>. </p></li>
</ol>
<h2>Finding common ground</h2>
<p>We need to keep sight of the fact that there is general agreement on 94% of listed species. By identifying the small number that are generating the greatest tension, it’s more likely discussions can be held to reach common ground on regulation.</p>
<p>Most countries in Africa don’t have invasive species regulations. But there’s growing recognition that they’re needed. South Africa offers useful lessons on how this could be done. </p>
<p>The control of species listed under the country’s biodiversity act is compulsory. This means that plans to manage them have to be drawn up and implemented. But this doesn’t seem sensible given that not all are equally harmful and resources are limited. Our study <a href="https://doi.org/10.4102/abc.v47i2.2160">suggests</a> that some of the species currently regulated could be removed from the list. </p>
<p>Countries wanting to set up a system of managing invasive species could start by classifying a prospective list of candidates. Policymakers could then quickly bring out legislation against the most damaging and destructive ones. At the same time, discussions could be had on the ones that generate conflict with the aim of reaching consensus.</p>
<p>This would allow managers and regulators to focus on the most destructive species – as well as those that are at the centre of fierce disagreement.</p><img src="https://counter.theconversation.com/content/79868/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Tsungai Zengeya receives funding from National Research Foundation, South Africa.
Affiliation: Centre for Invasion Biology, South African National Biodiversity Institute, Kirstenbosch Research Centre, Claremont, South Africa</span></em></p>Regulating species in South Africa is difficult. But identifying those creating the greatest tension, would shift focus on the most destructive species.Tsungai Zengeya, Researcher at the South African National Biodiversity Institute, South African National Biodiversity InstituteLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/794442017-06-22T13:20:06Z2017-06-22T13:20:06ZInvasive species have a massive impact, but wise policy can keep them out<figure><img src="https://images.theconversation.com/files/174706/original/file-20170620-30812-1yhyxff.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The American red swamp crayfish was intentionally introduced to parts of Africa to control snails and as a pet.</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p><em>This article is the second in a <a href="https://theconversation.com/topics/invasive-species-africa-40566">series</a> The Conversation Africa is running on invasive species</em></p>
<p>Invasive alien species harm ecosystems, economies and human health across the globe. In Africa, alien trees <a href="http://www.sciencedirect.com/science/article/pii/S0921800907006167">reduce water yield</a> in regions that are severely water stressed. Fishes introduced for aquaculture <a href="http://www.nationalgeographic.org/media/impact-invasive-species/">reduce native biodiversity</a> and alien whiteflies spread <a href="http://www.apsnet.org/publications/apsnetfeatures/Pages/cassava.aspx">diseases in cassava</a> that can lead to famine.</p>
<p>Many of these species were introduced intentionally for use as pets, crops, livestock, garden plants or for forestry. Overall trade between countries has greatly improved human welfare by giving access to useful species. In Africa, these intentionally introduced species include the food staples cassava and maize, which are both native to the Americas.</p>
<p>But the continent has learned the hard way. A subset of imported species have become invasive, and by the time they become established in the wild it’s almost always too late to eradicate them. </p>
<p>More species than ever are being moved intentionally around the world as the pace of trade between countries continues to grow. Most countries still operate with what is essentially an open door policy, allowing in any species that commercial interests want to import.</p>
<p>But there is a better way. Invasive alien species are different from alien species that don’t cause harm. Scientists have the techniques and the know how to track these differences and to predict which species are likely to become invasive in the future. This makes it possible to decide wisely which species are safe to import. The impact of invasive species can be massively reduced if policies are developed based on these insights.</p>
<p>Developing these policies would be financially and environmentally beneficial for all countries. But there are significant challenges to implementation, particularly in developing countries, where resources for assessing species and then monitoring borders are scarce. These challenges could be overcome by sharing the results of assessments on species among countries, and through cooperation between importing and exporting nations to prevent the transport of harmful ones.</p>
<h2>A basic biology</h2>
<p>It’s possible to predict the behaviour of species by looking at their basic biology, how they interact with the environment, and how they spread. Using basic analysis, it’s possible to predict which invasive species will be bad, and which benign.</p>
<p>Not all are bad. Take the mollusc populations of the US Great Lakes which is home to a number of alien snails and mussels. But only a few are harmful – like the notorious zebra mussel which causes hundreds of millions in damage by clogging pipes and has fundamentally rearranged the Great Lakes ecosystems.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/174734/original/file-20170620-30863-wk24dl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/174734/original/file-20170620-30863-wk24dl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/174734/original/file-20170620-30863-wk24dl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/174734/original/file-20170620-30863-wk24dl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/174734/original/file-20170620-30863-wk24dl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/174734/original/file-20170620-30863-wk24dl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=504&fit=crop&dpr=1 754w, https://images.theconversation.com/files/174734/original/file-20170620-30863-wk24dl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=504&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/174734/original/file-20170620-30863-wk24dl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=504&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Zebra mussels, an invasive species of fresh water mussels, on the propeller and shaft of a
sailing yacht.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>This and other harmful non-native molluscs in the Great Lakes are characterised by having <a href="https://www.researchgate.net/profile/David_Lodge4/publication/6505938_Fecundity_as_a_Basis_for_Risk_Assessment_of_Nonindigenous_Freshwater_Molluscs/links/53dab7350cf2631430cb10a8.pdf">much higher production of offspring</a> than their harmless counterparts. </p>
<p>And in South Africa, <a href="https://www.researchgate.net/profile/Richard_Cowling/publication/227677415_Assessing_the_risk_of_invasive_success_in_Pinus_and_Banksia_in_South_African_mountain_fynbos/links/56fd3ec708ae3c85c0c9bf8e.pdf">invasive pine trees</a> mature faster and produce small seeds that can be blown long distances to colonise new habitats. These harmful pines are out competing native species in some habitats, while species without these characteristics rarely spread from where they’re planted.</p>
<p>Alien species with a history of being harmful in one area are likely to <a href="https://www.researchgate.net/profile/Keith_Hayes2/publication/225567176_Are_there_any_consistent_predictors_of_invasion_success_Biol_Inv/links/00b49532d0d139e018000000.pdf">cause harm in another</a>. </p>
<p>Transferring this scientific knowledge to policy helps to make predictions about how imported species are likely to act in the future. Risk assessment tools have been developed to do this. Some countries -– notably <a href="http://www.environment.gov.au/biodiversity/wildlife-trade/live">Australia</a> and <a href="https://www.mpi.govt.nz/law-and-policy/legal-overviews/biosecurity/">New Zealand</a> -– have been implementing these for over a decade. They ban all species that have the characteristics of invaders, including most reptiles. </p>
<p>Many others, including the US, European Union, and South Africa, are moving in this direction. But progress is slow and there is opposition from companies concerned about regulations that restrict what they can buy and sell.</p>
<h2>Policy is crucial for developing nations</h2>
<p>Progress has been made in managing the import of species in developed countries, but there’s been less in developing nations. Poorer countries face big challenges in, for example, developing policies and monitoring borders. </p>
<p>But developing nations have the most to gain from keeping invasive species out because invaders have a big impact on agricultural production and fisheries that make up a large portion of their economies. For example, the American <a href="http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0104-64972015000100002">red swamp crayfish</a> was intentionally introduced to Africa to control snails and as a pet. But it soon escaped into the wild where it reduces harvests of aquatic plants and fishes, and can even destabilise dam walls with its burrowing. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/174735/original/file-20170620-30842-17av5i3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/174735/original/file-20170620-30842-17av5i3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/174735/original/file-20170620-30842-17av5i3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=896&fit=crop&dpr=1 600w, https://images.theconversation.com/files/174735/original/file-20170620-30842-17av5i3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=896&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/174735/original/file-20170620-30842-17av5i3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=896&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/174735/original/file-20170620-30842-17av5i3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1126&fit=crop&dpr=1 754w, https://images.theconversation.com/files/174735/original/file-20170620-30842-17av5i3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1126&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/174735/original/file-20170620-30842-17av5i3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1126&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The red swamp crayfish escaped into the wild where it can reduce harvests of aquatic plants and fishes.</span>
<span class="attribution"><span class="source">Reuben Keller</span></span>
</figcaption>
</figure>
<p>There are ways round the problem. Developing nations can use simpler methods to determine which species are likely to become invasive. The US <a href="https://www.fws.gov">Fish and Wildlife Service</a> has developed a useful approach to <a href="https://www.fws.gov/injuriouswildlife/pdf_files/ERSS-SOP-Final-Version.pdf">risk assessment</a> that relies primarily on determining whether a species is suited to climates in the new region, and whether it has become invasive elsewhere. The assessment can be adapted for any region, applied to any plant or animal, and has reasonable accuracy. </p>
<p>Another way to reduce the cost is for countries to share predictions. This would mean that the burden of assessing species was spread out. </p>
<p>And better coordination between exporting and importing countries could help improve border controls and ensure compliance. </p>
<p>Policies that predict which species are likely to become invasive and then keep them out would have huge environmental and economic <a href="http://onlinelibrary.wiley.com/doi/10.1111/conl.12071/full">benefits</a>. South Africa is <a href="http://www.abcjournal.org/index.php/ABC/article/view/2136/0">developing regulations</a>. It should consider using one of the risk assessment approaches that have already been shown to be effective. </p>
<p>Other countries in sub-Saharan Africa need to take action too. Acting together, countries will be able to keep out the next invaders, protect biodiversity, reduce future financial costs, and lessen future losses of vital ecosystem services.</p><img src="https://counter.theconversation.com/content/79444/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Reuben P. Keller receives funding from United States Environmental Protection Agency.</span></em></p><p class="fine-print"><em><span>Sabrina Kumschick receives funding from the South African National Department of Environment Affairs through its funding of the South African National Biodiversity Institute’s Invasive Species Programme and from the DST-NRF Centre of Excellence for Invasion Biology. </span></em></p>Developing countries have been slow to react to the alien species problem. Its impact can be massively reduced if policies are developed to deal with the issue.Reuben P. Keller, Assistant Professor Freshwater Ecology, Invasive Species, Bioeconomics, Loyola University ChicagoSabrina Kumschick, Researcher and core team member Centre for Invasion Biology, Stellenbosch UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/786842017-06-14T15:26:34Z2017-06-14T15:26:34ZAlien animals and plants are on the rise in Africa, exacting a growing toll<figure><img src="https://images.theconversation.com/files/173342/original/file-20170612-10193-b97g43.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The larger grain borer beetle attacks crops like maize and cassava, threatening food security.</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p><em>This article is the first in a series The Conversation Africa is running on invasive species.</em></p>
<p>Let’s say you’re travelling from Uganda to South Africa for business. You finally arrive at your hotel after a long day and decide to change before dinner. You unlock and unzip your luggage, but there’s something in your bag that you didn’t pack. As you reach for a clean shirt, a moth flies out. Did that come with you all the way from Uganda? It’ll be fine, right? Surely, something so small won’t cause any harm.</p>
<p>Species are intentionally or accidentally transported by humans between continents to regions where they are not native. With the help of humans or by natural means like flight, these alien species can also spread within continents.</p>
<p>Their spread within continents can be rapid, affecting both the ecology as well as societies and the economy. Unfortunately, it’s really challenging to prevent species from spreading. Given the vast amount of people and goods that are transported between and around continents they can easily be moved across oceans as well as between countries.</p>
<p>The spread of alien species within Africa is increasing. Since 2000 more alien insect pests of eucalyptus trees have spread to other African countries from South Africa, than have been introduced to these African countries <a href="http://www.abcjournal.org/index.php/ABC/article/view/2157">from other continents</a>. To manage the spread of these alien species countries need to <a href="http://www.abcjournal.org/index.php/ABC/article/view/2157">co-operate, communicate and share information and skills.</a>. </p>
<h2>The spread of alien species</h2>
<p>Many alien plants and animals have been introduced to Africa from other regions and then have spread from country to country, often having devastating effects.</p>
<p>Take the larger grain borer beetle, (<em>Prostephanus truncatus</em>) which is thought to have arrived on the continent in imported grain from Mexico and central America. The beetle was introduced to Tanzania before 1984, Togo before 1981 and <a href="http://www.abcjournal.org/index.php/ABC/article/view/2157">Guinea before 1987</a>. It then spread across the continent and within 20 years could be found further south in South Africa. </p>
<p>The beetle attacks crops such as maize and cassava, threatening food security and the <a href="http://www.cabi.org/isc/datasheet/44524">livelihoods of the poor</a>. Infestations often destroy maize that’s been stored by farmers, forcing them to buy maize as well as lose income they could have earned from selling any excess.</p>
<p>But alien species don’t just arrive from abroad. Many that are native to parts of Africa have also spread to countries on the continent where they are not native.</p>
<p>An example is the fish commonly known as the Mozambique tilapia (<em>Oreochromis mossambicus</em>) which is native to rivers on the east coast of southern Africa. Fishermen have transported the Mozambique tilapia to other areas and it is now found in river systems in southern and western South Africa and Namibia. </p>
<p>The Mozambique tilapia is a popular species for fishing but it can pose a threat to native <a href="http://www.iucngisd.org/gisd/speciesname/Oreochromis+mossambicus">fish</a> and has been responsible for the disappearance of native species in some <a href="https://www.fws.gov/fisheries/ans/erss/highrisk/Oreochromis-mossambicus-ERSS-revision-July-2015.pdf">regions</a>.</p>
<p>The spread of alien species within Africa is by no means a new thing. For instance, the bur clover (<em>Medicago polymorpha</em>), a plant from northern Africa, might have been accidentally transported by humans to South Africa <a href="http://www.abcjournal.org/index.php/ABC/article/view/2157">as early as 760 AD.</a></p>
<h2>A high and increasing threat</h2>
<p>Recently a number of alien species have spread extremely rapidly across the continent, posing a particularly high threat to food security and livelihoods.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/173341/original/file-20170612-10258-1rjje5i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/173341/original/file-20170612-10258-1rjje5i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/173341/original/file-20170612-10258-1rjje5i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=403&fit=crop&dpr=1 600w, https://images.theconversation.com/files/173341/original/file-20170612-10258-1rjje5i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=403&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/173341/original/file-20170612-10258-1rjje5i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=403&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/173341/original/file-20170612-10258-1rjje5i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=506&fit=crop&dpr=1 754w, https://images.theconversation.com/files/173341/original/file-20170612-10258-1rjje5i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=506&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/173341/original/file-20170612-10258-1rjje5i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=506&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The fall armyworm, native to the Americas, was first recorded in west and central Africa in early 2016 and then in South Africa in January 2017.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>One is a caterpillar known as the fall armyworm (<em>Spodoptera frugiperda</em>). The species, native to the Americas, was first recorded in west and central Africa in early 2016 and then in <a href="http://www.arc.agric.za/arc-ppri/Fact%20Sheets%20Library/The%20new%20Invasive%20Fall%20Armyworm%20(FAW)%20in%20South%20Africa.pdf">South Africa in January 2017</a>. </p>
<p>The moths of the armyworm are strong fliers and the species may have spread through flight to South Africa from other African countries. Although the species attacks a wide range of crops, it poses a particularly serious threat <a href="https://theconversation.com/armyworms-are-wreaking-havoc-in-southern-africa-why-its-a-big-deal-72822">to grain farmers</a>. It is extremely <a href="https://theconversation.com/why-its-hard-to-control-the-fall-armyworm-in-southern-africa-72890">difficult to manage</a>. </p>
<p>Another example is a wasp known as the bluegum chalcid (<em>Leptocybe invasa</em>), which is native to Australia. In 2000 it was <a href="http://www.fabinet.up.ac.za/publication/pdfs/1952-kelly_et_al_selitrichodes_neseri.pdf">detected in Israel</a> and shortly afterwards it was reported in <a href="http://www.forestry.co.za/uploads/File/home/notices/2011/ICFR%20IS01-2011gallwasp.pdf">Uganda and Kenya</a>. From there it spread rapidly to many African countries including Zimbabwe, Mozambique, and Tanzania and was finally detected in <a href="http://www.forestry.co.za/uploads/File/home/notices/2011/ICFR%20IS01-2011gallwasp.pdf">South Africa in 2007.</a> The insect probably reached Israel on live plant material and spread into Africa the same way, or was carried by people travelling between countries. </p>
<p>The wasp causes swelling or growths on eucalyptus trees, which can lead to <a href="http://www.fao.org/forestry/13569-05912e0e2fe9054c3ed4904ae597e3310.pdf">decreased growth and tree death.</a> As eucalyptus trees are an important source of income and fuel, this species could have an impact on the livelihoods of locals in these countries.</p>
<h2>Preventing the introduction and spread</h2>
<p>Once a species is introduced to one African country it’s highly likely it will spread to others on the continent because borders checks are weak.</p>
<p>The introduction and spread of species could be reduced if countries introduced biosecurity systems. These are used extensively in countries like Australia and New Zealand and involve using technology to check for alien species when people and goods enter a country. In Australia this involves inspecting goods, vehicles and luggage before they enter the country.</p>
<p>But even these systems aren’t a guarantee that species won’t spread. African countries would need to work together and share information and skills. This would also allow countries to prepare for the arrival of species, and to draw up plans to reduce their impact.</p>
<p>This is a tall order. But as a country’s defence against alien species introductions is only as strong as that of its neighbours, such action would benefit all of the countries involved.</p><img src="https://counter.theconversation.com/content/78684/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Katelyn Faulkner receives funding from South African National Biodiversity Institute's Invasive Species Programme. </span></em></p><p class="fine-print"><em><span>Mark Robertson receives funding from the DST-NRF Centre for Invasion Biology. </span></em></p><p class="fine-print"><em><span>Brett Hurley does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Many alien plants and animals have been introduced to Africa from other regions and spread from country to country, often having devastating effects.Katelyn Faulkner, Postdoctoral research fellow, University of PretoriaBrett Hurley, Senior Lecturer Zoology and Entomology, University of PretoriaMark Robertson, Associate Professor Zoology & Entomology, University of PretoriaLicensed as Creative Commons – attribution, no derivatives.