Japanese Knotweed in Hemel: The Nickey Line Nightmare

Over the course of this blog I've covered invasive species problems from all over the world. Now I have come across a case much closer to home. Within a few miles, in fact, of the place I call my own, Hemel Hempstead, in South East England.

It gets called plenty, but I call it home...

Famous for giant oil explosions and recently being voted the UK's ugliest town, the latest travail it is encountering is the invasion of Japanese Knotweed on the rather nice Nickey Line pathway.

Japanese knotweed is native to Japan, Korea and China and was introduced to Britain in the 1850s (Bailey and Conolly, 2000). It is regarded as the most pernicious invasive weed in the British Isles (Mabey, 1996) and since 1981 it has been a criminal offence to introduce Japanese Knotweed (Hollingsworth and Bailey, 2000).Despite this, halting it's spread has proved impossible.

Distribution of Japanese Knotweed, then and now. Source: Cabi.org

It is an aggressive invader that causes substantial economic and environmental damage in the UK (Smith et al., 2007). Amongst these include impacts on native flora, increased flood risk, physical damage to buildings (its roots can grow through concrete) and it can obstruct public access to certain areas (ibid). The plant is problematic to remove as it spreads from its rhizomes rather than seeds (Environment Agency, 2013).
 

No place for a plant: Japanese Knotweed growing through a wall.

Luckily the local council is taking the required action in the very near future. Drains are to be replaced and improved, new tarmac will be layed on the path and the plants will be treated and removed.

In an attempt to ensure the hardy plant doesn't continue to grow or return, a large area around the plant will be excavated to a depth of about 3 metres. The dug up earth will be sent to a special landfill and a copper shield is to be inserted before the area is restored.

A site of Japanese Knotweed removal in nearby Watford, looks...rooty...?

If you happen to spot any possibly harmful plants in the Dacorum Council area, you can call the trees and woodlands department of the local council on 01442 228000.

Over and out

The Invader Inspector

Inspecting Invaders Christmas Edition!

Merry Christmas everyone! The day is now upon us so I feel much more comfortably saying it than I would if it was the start of November. That's right Tesco, it's not ok to have Christmas stuff on the shelves that early. For shame.

Anyway, rant over, you're probably here to read about invasive species. Today's piece is gonna full of seasonal cheer, but factual and sciency and stuff at the same time. A real Christmas cracker you could say!

To make the piece extra festive, I thought where better to rankle a case study from than Christmas Island itself! In my mind, it's permanently snow covered, the lamp posts are candy canes and everyone gets merry with Pierre Noel himself at the local on Friday night.

Merrrrry Christmas!!! First round of samichlaus is on him!

In reality, it's in the Indian Ocean. So probably not climatically suitable for permanent snow cover, but I hope they make the effort with the candy canes...

Location map of Christmas Island

In even starker reality, the island is suffering from an invasive species drama of Dickensian proportions. Playing the roles of synergistic villains, step forward Pulvinaria urbicola Cockerell (almost sounds like a name Dickens would come up with!) and yellow crazy ants.

Pu. urbicola is a honeydew producing scale insect and notoriously destructive invader (Gaigher et al., 2011). It has great reproduction potential and can become widespread on tropical islands And here's the Christmas crisis... it's been detected on Christmas Island (Neumann et al., 2014)! Oh no!

Pulvinaria urbicola, the scoundrel desecrating Christmas Island.

Introduction of Pu. urbicola to Christmas Island is likely anthropogenic; largely associated with movement of plant material to the island.

And the situation is bad. Christmas Island has experienced a large-scale ecosystem 'meltdown' (O'Dowd et al., 2003) as a result of interactions between scale insects, such as Pu. urbicola, and invasive yellow crazy ants.

Honeydew producing insects are a major problem. Not only do they themselves damage plants, they serve as mutualistic partners for invasive ants, exacerbating their impacts (Abbott and Green, 2007). Large populations of scale insects cause forest dieback, while increased honey dew levels facilitate the yellow crazy ants.

The ants themselves cause rapid, catastrophic shifts to tropical forests, affecting at least three trophic levels (O'Dowd et al., 2003). They extirpate red land crabs, the dominant omnivorous forest floor consumer, overwhelming them by their sheer numbers and bump them off by spraying formic acid into their eyes and mouths. The ants then occupy burrows and consume resident crabs. Starting to see where the 'crazy' bit of their name comes from...

The loss of crabs caused by this invader indirectly releases pressures on seedling recruitment and slows litter breakdown. The impact of which can be prettyyyyy big. 

Impacts of the yellow crazy ant (a) shows an univaded site, maintained by foraging red land crabs (b) shows a site 1-2 years after invasion.

In June and July of 2011, heavy infestations of Pu. Urbicola were discovered on Pisonia Grandis, a tree species on the south coast of the Island. 12 of 15 trees sampled had Pu. Urbicola presence, with 5-60% of leaves on each tree infested. And, of course, attracted by the honeydew they produce, yellow crazy ants were found nearby (Neumann et al., 2014).

Pisonia grandis forests are important to the island ecosystem, providing nesting and roosting habitats for sea birds and regulating understory vegetation. However, the tending of Pu. urbicola by invasive ants is implicated in the dieback and decline of Pisonia Grandis (Neumann et al., 2014). Climate change is also implicated in the forest decline, but there is strong evidence this is a secondary factor.

A Pisonia Grandis forest

At present there is no feasible chemical option for direct control of Pu. urbicola, and it is not significantly predated on Christmas Island (Neumann et al.,2014). However, biological control could be an option as introducing scale insect predators has aided suppression on oceanic islands (Smith et al., 2004).

So Christmas Island is facing a tricky situation, with three species seemingly intertwined in the threats faced by the Island's forest ecosystem. These interactions make the situation even harder to manage, but a biological control programme for Pu. urbicola on Christmas Island is underway.

I hope it proves to be successful, but am unsure of the effects that extirpating Pu. urbicola will have on the yellow crazy ant, which seems to be the greater issue... we can only wait and see what happens.

So that wasn't as festive as I'd hoped... I mean, a story about crabs being sprayed with acid and forests dying doesn't really embody the spirit of Christmas. I think that needs fixing...

Do you remember the piece I did earlier this year on the decline of red squirrels due to the invasive greys? Well those greys have now reached Santa Claus himself, and one cheeky little blighter has even stolen his hat! They really are causing havoc everywhere it seems!

The most heinous of crimes.

I hope he finds the delinquent squirrel soon, or he'll probably be very chilly when he's out delivering our presents. I know I'll be keeping my fingers crossed for the hats safe return.

Merry Christmas

The Invader Inspector

Invasive Species and Human Health - Imminent Illnesses in Europe?

In my previous two pieces on the impact of invasive species on agriculture, some examples of invader facilitated diseases cropped up (no pun intended...). This got me thinking, if invasive species can cause ailments to our farming activities, can they have direct negative effects on humans too?

I knew that mosquitoes cause diseases like malaria and dengue fever. I also knew that with changes in climate, their distributions are changing. So, I figured it was worth investigating further... with emphasis on Europe, so it has some 'closer to home' relevance.

Mozzies are vectors for a number of diseases including yellow fever, dengue fever, malaria and chikungunya (Akbari et al., 2013). Picking out dengue specifically, approximately 2.5 billion people worldwide are at risk, with approximately 25000 deaths a year (Guzman and Isturiz, 2010).

Aedes aegypti is the principal species facilitating Dengue spread (Halstead, 2008) and it's also responsible for outbreaks of chikungunya (Ligon, 2006). It is native to tropical Africa (Braks et al., 2004) but expanding in range, with Dengue occurrence closely following this expansion (Guzman et al., 2010).

A female Aedes aegypti, you don't want to encounter one...

In October 2012, Aedes aegypti was implicated in a large outbreak of Dengue fever in Madeira, Portugal (Sousa et al., 2012). By early 2013, more than 2000 cases had been reported (ECDC, 2013).

Notified dengue fever cases by week, Madeira, Portugal, 3 October - 25 November 2012. Source: Sousa et al., (2013)

So, maybe soon we'll need vaccinations before we go on holiday to some of Southern Europe? And I can't see 'Sun, Sea and Possible Chances of Deadly Diseases' catching on in travel brochures anytime soon...

Another concern is the Asian Tiger Mosquito, Aedes albopictus, an aggressive species with vectorial capacity for a number of nasty aforementioned diseases.

It is native to East Asia, but is expanding globally at a rapid rate, having colonised every continent bar Antarctica in the past 40 years (Bonizzoni et al., 2013). In the last 10 years the species has been the principal cause of Dengue and Chikungunya outbreaks in Hawaii, Central Africa, southern China and now, Europe too (Bonizzoni et al., 2013). Quite a spread, I'm sure you'd agree.

Aedes Albopictus: currently the most invasive vector species worldwide (Bonnizoni et al., 2013).

Focusing specifically on Europe again, the Tiger Mosquito was first recorded in Albania in 1979. It's now present in all Mediterranean countries and is moving north to countries including Belgium (Bonizzoni et al., 2013).

The Tiger Mosquito was the cause of the first notable invasive mosquito-borne disease outbreak in Europe. In the summer of 2007 in Ravenna, Italy, more than 200 cases of chikungunya were reported (Angelini et al., 2007). 

It's globetrotting nature presents a threat. Between 1990 - 2013, the number of people living in countries with Tiger Mosquito presence has increased from 3.2 - 5.1 billion.  The species is highly adaptable ecologically, can transmit many pathogens and is happy in both urban or rural locations. So, it's not just a globetrotter, it's also cosmopolitan. That could be an issue...

Global distribution of Aedes albopictus, now available in Western Europe! Source: Bonizzoni et al (2013).

Concerns over mosquitoes are rising as they have spread considerably since 1990 (Schaffner et al., 2013). Changes in weather patterns and land cover are known to impact vector borne disease transmission (Vanwembeke and Lambin, 2006). Climate change could also facilitate higher mosquito densities and spreads beyond current boundaries.

However, the principal driving forces for the spread of mosquito borne diseases have been anthropogenically driven, due to globalisation and inefficient public health measures (Schaffner et al., 2013). 

On the other hand, it is worth pointing out that other invasive mosquitoes such as Aedes Atropalpus and Aedes koreicus currently represent very low threats to European public health (Schaffner et al., 2013).

Aedes Atropalpus: not as much of a health concern.

Generally though, given these developments, mosquito surveillance is now essential to detect early invader presence and prepare for control of disease outbreaks (ECDC, 2012). Early eradications have been achieved for certain mozzies in France, Italy and the Netherlands (Schaffner et al., 2013).

Another invader I came across with the potential to inflict disease upon humans was Nyctereutes procyonoides, or, as we more commonly know it, the raccoon dog. Historically, it was restricted to the Far East, however, it now has a presence in much of northern and eastern Europe, with potential to expand further (Kauhala and Saeki, 2004).

The Raccoon Dog's native range (blue) and invaded areas (red).

The danger posed by raccoon dogs is their ability to transmit the potentially lethal viruses to humans, including rabies. In fact, as many as 55,000 humans are killed by rabies every year. The concern in Europe is that the racoon's flexible habitat use, high offspring numbers and large dispersal potential could lead to high population densities (Sutor et al., 2013).

Raccoon dogs, cute but be careful.

However, it should be pointed out that countries such as Finland and Germany have raccoon dog presence, but are also rabies free. And more generally, it seems the raccoon dog poses greater threats to wildlife than to humans in Europe. So I don't think we need to worry about large quantities of people foaming at the mouth anytime soon.

To conclude, there is ample evidence that we should be concerned about the impacts of invasive species with regard to human health, particularly concerning certain species of mosquitoes. The growing threat is entwined with global environmental change, anthropogenic and 'natural', as this is permitting the spread of the potential disease inflictors. Should we be concerned? I'd have to say yes, and if we're aware of the threat now, it should help mitigate the effects in the future.

Uninvadable Agriculture?: Cubes, Corn and Creepy Crawlies

Today's piece represents a unique situation for Inspecting Invaders. That's because I'm not going to talk about invasive species at all, well, except to make reference to a lack of them.

In my previous post, I painted a slightly worrying picture about how invasive species are reducing agricultural yields, and how this is set to become worse in the future.

However, during a recent reddit procrastination session, I stumbled across a link to this article on how it seems nothing can live in a corn field apart from corn. And it got me thinking, is this uninvadable agriculture?

The article discusses stories from two interesting books. The first is A World in One Cubic Foot, by David Liittschwager (a portrait photographer) and E.O Wilson (a Harvard biologist) (cool tag-team). David spent years travelling round the world, dropping one-cubic-foot metal frames into all sorts of environments, and the species he found were documented.

For example, in a Costa Rican tree, the aforementioned cube was found to contain more than 150 different plants and animals.

A cube hanging out in a Costa Rican tree top...

...and the species it was found to contain.

Countering this, scientific writer Craig Childs, tells the story of species surveys in a 600 acre Iowan cornfield in his new book, Apocalyptic Planet. The results bore a stark contrast to the Costa Rican tree census. This is because corn farmers really really value their corn. Anything which may eat, hunt or even bother it, is killed. The corn is also bred to fight pests. the ground is sprayed, with stalks sprayed again. Cause you can't be too careful.

A corn field. Plenty of corn not much of anything else.

In three days and two nights, he only came across one tiny ant, a minuscule mushroom, a single spider, a single red mite and some grasshoppers.

Yep, not much here apart from corn.

This is even more stark when considering that these prairies were once home to a rich variety of species. Now they're home to pretty much just one living thing.

Clearly this is good for food supply, but is it worth the loss of biodiversity? My opinion is that if the loss of biodiversity remains localised, species invasions are prevented, and sufficient corn yields are produced, then there is no issue with a farm taking precautions to ensure its productivity.

We need to be careful though with what we apply to our crops with regard to human health, as this blog post by Laura Tamjarv on an Argentinian atrocity demonstrates.

That's just my opinion, as the use of pesticides and such like is a delicate issue I'd be very interested to hear any thoughts anyone reading this may also have.

Over and out

The Invader Inspector

Invasive Species, Agitating Agriculture?

Well that management section was fun, I can barely remember what it's like to write about anything else. But the past is the past, I need to knuckle down and rattle through some more invasive species related capers. So, onwards we go!

When I was chatting with Hugo Watkins the other day about his farming blog, I flippantly asked him if he'd done a piece on the impact of invasive species on agriculture yet. That very second, the cogs in my brain slowly clicked into action.

An actual X-ray of the inside of my skull.

*Wait, I've just suggested something invasive species related...that means... Gah I know the answer to this one..*

...15 minutes later...

*That means I can write about it!*

And write about it I shall! Because it turns out, the impact of invaders on agriculture has been quite a big deal. AND it's likely to increase in future.

So, whereas Hugo's blog discusses how agriculture is contributing to environmental change, I'm looking at how environmental change is contributing to agriculture. Neat, huh?

Invasive species and agriculture, how costly could the impacts be?

Earth is now home to over 7 billion hungry humans, and we're heavily reliant on agriculture for food. However, invasive species can cause agricultural product losses worth more than a trillion US dollars per year (Oerke and Dehne, 2004). According to Ziska et al (2011), in their 'agronomics'  paper, ¹/₄ of U.S.A's gross agricultural product is lost to invasive species each year. Yipes.

For example. Asian soybean rust (Phakopsora pachyrzi), an invasive pathogen, has potential to inflict major soybean production damage in the U.S.. It is thought to have arrived from South America in 2004, having been carried by Hurricane Ivan. In future, with storminess expected to increase under climate change, its spread and negative agriculture effects could become worse (Ziska et al., 2011).

U.S states with confirmed detections of Asian soybean rust in 2006. Source: Economic Research Service

Invasive weeds can also pose agricultural problems. For example, Follak and Essl (2013) have documented the spread and agricultural impact of Sorghum halepense, an emerging invasive species in Central Europe.

The Central Asian native first arrived in Austria in 1871, was rare until 1970, but has expanded rapidly since 1990 and even more so since the new millennium. The S. halepense invasion puts approximately 41% of maize fields and 40% of oil pumpkin fields at risk of yield losses.

Cumulative records of S. halepense in Austria. Source: Follak and Essl (2013)

S. halepense can also act as a reservoir for Maize Dwarf Mosaic Virus (MDMV). Evidence for this comes from N. Italy, where S. halepense is widesprad and MDMV is commonly found on maize plants (Ivanovic et al., 1995), and Hungary, where yield losses from maize fields were reported to be up to 30.5% (Peti, 1983 cited in Ziska et al., 2011). 

Sorghum halepense, reducing Austrian agricultural yields since 1871.

The fast and ongoing spread of S. halepense is likely to increase under climate warming as more habitat becomes suitable.  In fact, all major agricultural areas in Austria and Germany expected to be climatically suitable by 2050 (Kleinbauer et al., 2010).

Additionally, management is troublesome, given that it has high seed production, high regeneration potential and is only sensitive to specific, high cost herbicides (Follak and Essl, 2013). Double yipes.

Invasive insects can also initiate farming frustrations. For example, African honey bees are moving north through America. These invaders readily capture feral and managed European honey bee colonies, with subsequent impacts on fruit production. Once again, this spread is likely to be facilitated further by climate warming (Ziska et al., 2011).

Current and projected range of Africanised honey bees. Black areas are where it is currently present. Grey areas represent the area that could support the bee if there are 120 days where the max temperature is >10°C

An even more serious insect invasion took place at the start of the 20th century when the introduction of the boll weevil (Anthonomus grandis) to the U.S. from Mexico resulted in almost the complete eradication of cotton crops in the U.S., with billions of dollars of crop damage (Ziska et al., 2011).

The risk to agriculture from invasive species is only likely to increase in future, not just due to rising temperatures, but also potentially from heightened winds and CO₂ increases. These factors could also interact. For example, the invasive weed, Kudzu, is known to respond strongly to CO₂ increases (Forseth and Innis, 2004) and is likely to move north as temperatures increase (Sasek and Strain, 1990).

Increasing CO₂ concentrations have been shown to increase the biomass of invasive kudzu.

The impacts of this on agriculture will be heightened by the fact that Kudzu can act as a host for Asian soybean rust, which I described above. Treble yipes.

This post has been a bit of a downer so far, so I should probably try and lighten the mood. Our food supply isn't completely doomed. We must also recognise the response of agroecosystems themselves to climate change. For example, rising CO2 could be used by breeders to improve existing cultivars. This could enable them to become more competitive against potential invaders and reduce productivity losses (Ziska et al., 2011).

To conclude, invasive species have been agitating agriculture for quite some time, and look likely to be an even greater annoyance as we move into the future. We should be aware of the impact invasive species can have on important ecosystem services, such as agriculture, and do our utmost to ensure that the future impacts of invaders are not as damaging as it looks like they could be.

Over and out

The Invader Inspector

Managing Invasive Species: Conclusion

Today marks the end for the 'Managing Invasive Species' chapter of this blog. I could keep going but no one likes a series that goes on for too long (Lost, I'm looking at you...). I'm taking the all good things must come to an end approach and retiring it at its peak.

Beginning with a recap, most conservation biologists believe that species invasions should be prevented wherever possible (Larson et al., 2013), however the methods for doing so are extremely wide ranging.

Aim for prevention where possible, things can escalate quickly once that threshold had passed. Source: Invasive Species Ireland

The first management approach I tackled was eradication. This was frequently effective in its initial aim of wiping out 'Invasive Species X' but often had negative side effects and could be expensive when taking account of environmental monitoring afterwards.

Second, I looked at legislation. In principle, this seemed to be a good idea. However, implementation of policy, especially at the international scale, was fraught with difficulty and often unable to become effective.

Next I looked at some alternatives. The strategy of human consumption (A fellow invasive species blogger has also recently analysed this strategy.) is thought to be potentially effective for Asian Carp management in the U.S.A. However at this early stage, it's difficult to be sure. Additionally this approach falls down by the fact that there are plenty of inedible invaders. 

I also considered biotic resistance, where we, as humans, don't act, and we allow natural predator-prey relations suppress the invaders. There was a case where this appeared to work, but it clearly isn't always effective, otherwise I guess there would be no prevailing invasive species! And this blog would be short on material...

Finally, I looked at public participation (for more on the related topic of 'Citizen Science' check out a recent post by Rachel Harris here). This approach has been effective at halting the spread of the Killer Shrimp in the UK, and it's cheap, but it is heavily reliant on the fact that people give a damn. And, maybe I'm bitter, but I don't think everyone does... And of course, there is plenty the public are plainly unable to do due to lack of resources.

So, all of these analysed. All with some good points, all with some bad. What is our best option?

In my opinion, when we uncover a potential troublemaker of an invasive species, we need to consider all the possible options for approaching its management. I mean, what would be the point in eradicating something when we can find a human use for it?

Research is clearly the key to choosing the best management approach for each individual case. Heck, it may even suggest a combination of approaches as the best way forward. I'm sure there are plenty of members of the public who would be up for removing invasive weeds rather than pumping in chemicals to eradicate them. 

Overall, here are some key point to take from this management series:

1. Where possible, the most effective course of action is, of course, to prevent invasive species establishing.
2. If dealing with an established invasive species, treat each case uniquely, and take the best possible action after considering all available evidence.
3. There is no 'one size fits all' solution to invasive species management. The benefits and costs of each approach should be accounted for in each case.

Invasive species management process cycle, note the high number of stages before implementation itself. Source Invasive Species International

When I started this series, I knew that I wouldn't find 'an answer' on how to manage invasive species, so to speak, but rather engage in a discussion of possible options to highlight the very fact that there isn't 'one'. There have been successes and failures when it comes to managing invasive species regarding all the strategies covered, but hopefully, as our ecological knowledge grows, the former will soon greatly outweigh the latter.

Over and out

The Invader Inspector

Management Approach 3: Alternatives

So far in this series of management posts, we've looked at two of the major players. eradication and legislation. Today I'm going to cover three slightly more out there methods, namely: human consumption, letting nature deal with it (biotic resistance) and public participation. 

Without further ado, let's kick things off with consumption. Ever had hunger pangs and thought to yourself *man, I would kill to chow down on an invasive species right now*? Well, me neither. But that doesn't mean that we can't, right?

Y'know, in certain cases anyway, I'm not suggesting going to your local park and nibbling on a grey squirrel. The likely outcome of that would be a court date and/or a rabies shot, which would be difficult to stomach.

On the other hand, the brilliantly named journal, Appetite, has recently published a piece highlighting consumption of Asian Carp in the U.S as a management strategy.

Over the past 20 years, Asian carp have invaded lakes and rivers in the Midwest and southern United States (Varble and Secchi, 2013) . The effects of this have been negative for many native fish, including the bigmouth buffalo and gizard shad (best names ever?), which have died off due to habitat encroachment resulting in food and space competition (Irons et al., 2007).

Map of Asian carp locations in the U.S.A

Mississippi River. Asian Carp. Everywhere... who's hungry?

Thus, the strategy of harvesting the cantankerous carp for human food has been put forward as a solution. And it's a promising one too. Most respondents were willing to try free samples and would be willing to pay for it (Varble and Secchi, 2013).

Creating demand for Asian carp could most definitely be a cost-effective solution to the problem. However, trouble could emerge if it becomes too popular. This could lead to farming of the species, which of course, would be bad for natives. Let's hope Americans are only moderate fish fans...

Moving on from our starter to the second course of the day, how does nature itself respond to the threat of invasive species?  Well, as the number of invasive species are increasing globally, more and more native predators are shifting their diets to invasive prey (Bulté et al., 2012). Handy, huh? Especially as this shift can be pretty rapid (Carlsson et al., 2009).

For example, >90% of the threatened Lake Erie water snake now consists of Eurasian round goby, which invaded the Great Lakes in the early 1990s (King et al., 2006). See the video below for a demonstration.

But, the real question is, do the predators actually suppress the invaders? Well, it seems that they can! Gruner (2005) reports an 80 fold increase in an invasive spider in absence of a native bird which was preventing it from becoming hyper-successful. Referred to as 'biotic resistance' (which sounds like some kind of environmentalist uprising), it seems like a viable way to 'manage' invaders.

However, it's not perfect. There can be substantial lag times in native diet adaptation, in which time negative impacts can arise in a given environment and possibly negative fitness affects on the natives themselves (Carlsson et al., 2009). (Bulté et al., 2012) suggest that in certain cases, natives could become more exposed to nasty parasites. Looks like biotic resistance faces resistance of its own then...

Finally, to cap off the triple header, what can we, as Average Joes, do to manage invasive species?

In the case of invasive aquatic plant (IAP) management, education is key (Willby, 2007). The principal pathway for IAP introduction is via horticultural suppliers (Keller and Lodge, 2007), but invaders such as Lagarosiphon major, can also be acquired online. It is vital that we know what we should and should not be planting in our gardens to prevent the spread of potentially dangerous invaders.

Another case of public participation relates to the spread of the Killer Shrimp (Dikerogammarus villosus), a serious freshwater invader which arrived in Britain in 2010 (Madgwick and Aldridge, 2011). In Europe it has preyed on or outcompeted native shrimp to the extent of excluding them from their natural habitat (Kinzler et al., 2009).

How to identify a killer shrimp

The species cannot be eradicated, and we know that it is spread by recreational water users, hence a containment strategy with public involvement has been implemented by Defra. Known as the Check Clean Dry campaign, water-users are encouraged to employ simple biosecurity practices to prevent the spread of the killer shrimp and other invaders. Early signs suggest that the campaign is being successful (Madgwick and Aldridge, 2011), but for this to continue, it will require all water users to be vigilant.  

Check, Clean, Dry. Follow these instructions to prevent the spread of aquatic invaders.

Well, that concludes today's agglomeration of case studies. Three very different approaches, all with potential to be effective in different situations, yet all with their flaws as well. That's been a pretty consistent theme throughout though, hasn't it?

Next time I'm going to wrap up this management series with a short conclusion piece which will tie everything together.

Over and out

The Invader Inspector

Management Approach 2: Legislation

ORDER!!! *Bangs gavel* . Today I've taken a seat at the front of my imaginary courtroom, ready to pass judgement on the effectiveness of invasive species legislation. Hope there aren't any objections to this. If there are... talk to my lawyer...

According to De Poorter (2009) legal arrangements are crucial to support and underpin practical management, particularly in protected areas. For example, Sivakumar (2003) documents the example of the Andaman Islands (see location below)  which have been experiencing biodiversity reductions from invasive species, including elephant and chital.

Location of the Andaman Islands, part of India's territory... over 1000km from the Indian mainland.

However, these invaders cannot be removed as they are native on the Indian mainland and covered by the Indian Wildlife Protection Act. Clearly painting the Andaman Islands with the same legislative brush as the Indian mainland is not good practice... I mean look far apart they are! This shows a key drawback of national legislation, a species can cause problems in one part of a country but be ok in others.

Moving from the national to the international, there are now over 50 internationally agreed legal instruments to deal with some aspect of invasive species (De Poorter, 2009). An interesting international agreement to observe is the International Convention for the Control and Management of Ships’ Ballast Water and Sediments, or, thankfully, BWMC for short. This was adopted in 2004 with the aim of controlling, the threat of invaders from ballast water. 

I think I mentioned this briefly in an earlier piece, but here’s a few fun facts to give an idea of why this is important to manage:

1. Everyday about 3000 species are transported around in ship’s ballast water or on their hulls.
2. Increasing volumes of trade, travel and tourism have led to more species than ever before being transported around the world (Carlton, 1999).
3. Introduction of invasive marine species by ships is one of the four most significant threats to the world’s oceans.

Marine invasive species presence is closely linked to shipping routes.

With a sea area of 3,000,000km², rich marine biodiversity and increasing international trade, China faces particular concerns over marine invaders (Liu, 2013). The Marine Safety Administration (MSA) is responsible for ballast water management and they don't inspect for invasive species. 

Wait, what? What about the BWMC that was adopted in 2004? Surely they HAVE to inspect for them?

Well, China has not actually adopted the BWMC regulations. In fact, nobody has actually implemented them yet. The MSA has no legal obligation to inspect ballast water as BWMC has not yet entered into force. Yes, despite the BWCM being adopted in 2004, it does not come into effect until 2016.

See the thing is, it was all well and good coming up with these regulations in 2004, but to actually come into force it required ratification by 30 states, representing 35% of world merchant shipping tonnage (De Poorter, 2009).

When it does come into force requirements will include conducting ballast water exchange at least 200 nautical miles from the nearest land and in water at least 200m in depth. Ships will also need to have a ballast water record book and implement specific management plans.

The mechanism by which ships can transport invasive species via their ballast water.

But I mean, 12 years is a loooonnnng time from adoption to implementation. It seems there are several reasons why international legislation is often slow to come into force. Negotiations can be lengthy as countries have different management capacities and priorities. This often also means legislation lacks strict rules, instead using words such as ‘as possible’, which is far from ideal.

However, it appears that it's not all doom and gloom with regards to legislation.  In the north-east U.S.A the presence of proactive legislative policies have reduced the likelihood of invasions by Orconectes rusticus (the rusty crayfish), IF regulations prohibited the transport of ALL live crayfish species between water bodies (Dresser and Swanson, 2013). Regulations that did not explicitly prohibit transport or prohibited only rusty crayfish were not effective. This suggests that the most effective form of legislation is one which does not require individuals to identify species.

Distribution of the rusty crayfish in the U.S.A., highlighting where it is considered native and invasive.

Additionally, regulations haven't been able to prevent dispersal based invasions across state boundaries through shared stream connections. Essentially, we can legislate against their anthropogenic spread, but it's hard to get nature to pick up a pen and sign on the dotted line. 

So now that substantial evidence has been presented what's my verdict on legislation? It seems that the approach can often be guilty of general ineffectiveness. In many cases this is because it doesn't actually become implemented, or when it does, it fails to take account of economic and ecological complexity, especially when tackling international issues. Overall, the jury's out on legislation as an effective management tool.

Over and out

The Invader Inspector

Management Approach 1: Eradication

As promised a few days ago, time to get stuck into some invasive species eradication, defined by Parks and Panetta (2009) as 'the permanent removal of entire discrete populations'. See Fig.1 below for a concise summary.

Fig. 1: The principle of invasive species eradication in a fun meme.

Sounds serious don't it? It's also much easier said than done, especially if you want to do a decent job of it.

Starting with the fundamentals, determining eradication feasibility is essential. However, as each case is unique this is often problematic. Despite this, attempts at setting criteria include:

1. The average rate of removal in populations must be > the annual intrinsic rate of increase.
2. There is no immigration of individuals that can breed.
3. And there must be no adverse effects . For example, on Sarigan Island feral goat eradication caused the eruption of an exotic vine (Kessler, 2002).

Another large factor towards feasibility of eradication is scale. For example, when trying to eradicate an aquatic invasive from a small pond, it can simply be drained, but this obviously cannot be done to larger water bodies (Parks and Panetta, 2009).

So yeah, Captain Obvious called and he said he wants his manual back... but even though these rules should clearly be applied, that of course doesn't guarantee that they are...

An example of a less than ideal eradication attempt has recently taken place within the Rondegat River, South Africa, regarding the smallmouth bass (Micropterus dolomieu)  (Jordaan and Weyl, 2013). The area has high fish diversity and endemism (Linder et al., 2010) but the threat of the invasive bass was perceived to be large, hence their removal was made a conservation priority.

A (slightly grumpy looking) smallmouth bass. Mind you, I'd be grumpy if someone tried to eradicate me.

To eradicate the bothersome bass, the pesticide rotenone was put into the river. This substance is highly toxic to most fish but non toxic to plants, birds and mammals (at low concentrations) and does not persist in the environment. Happy days, right?

Wrong. Despite tests being carried out, twice the recommended lowest effective rotenone dose was applied. This caused mortality in non target fish species and macroinvertebrates. Woops... and so much for point number 3 in our feasibility criteria...

The appliance of rotenone could also raise debates over animal cruelty as it blocks fish respiration and causes erratic swimming. An unpleasant experience for them, I'm sure you'd agree.

Moving from the specific to the general, there are arguments that eradication is often a human preference rather than a prerogative grounded in science (Marris, 2005). In the U.S.A they spend over $1 billion annually on invasive species 'control', featuring strike teams to 'pull, poison or burn' anything out of place, in the name of 'making an area liveable for native plants'.

A park ranger applying blue herbicide to invasive weeds.

But is this large expenditure necessary? Most new plant species manage to co-exist with what's already there; only a small percentage prove to be truly invasive. Perhaps instead of blindly eradicating non-native species, we should identify and ameliorate problems, using past cases to show whether or not a problem will even emerge?

However, where eradication has been easier and more successful is on islands, which harbour nearly half of the world's endangered biodiversity. Howald et al., (2007) report that concerning eradication of island rodents, there have been 332 successes Vs only 35 failures, mostly thanks to successful use of rodenticide. 

Location and size of islands where successful rodent eradications have taken place, note the majority are for islands <100ha (Howald et al., 2007)

For example, the Juan Fernández Archipelago, approximately 700km west of Chile, is a biodiversity hotspot threatened by invasive species. A multi-species program was undertaken as this lowers the cost associated with treating species individually. In this location, eradication of rodents also aided eradication of feral cats (Glen et al., 2013).

Eradicating rodents can assist when it comes to getting rid of feral cats.

On the other hand, even island eradication can be complex, particularly on those which are large (see graph above) and human inhabited. For example, toxic baits that are often used to eradicate invertebrates can't be used in areas where they would provide a risk to humans or domestic animals.

There are also ecological complexities associated with the process, with secondary outcomes including release of other invaders, decline of natives (as happened in South Africa) or environmental changes that can make it harder to eradicate other invaders (Morrison, 2007).

And we must remember the word 'permanent' in the definition. That's very hard to achieve, particularly when trying to eradicate weeds which can have extensive and long lasting seed banks (Gloria et al., 2012). It also requires long-term funding and effort, which is often not provided.

Before the 1980s many were sceptical about eradication (Parks and Panetta, 2009), but it is now considered a primary option. However, as we've seen, the process is often fraught with complexity.

Overall, it is important to plan the attack and allocate resources with great care, taking account of species interactions and providing a contingency plan if something goes awry. Research is ongoing to develop species-selective toxins and control devices to target pests without endangering non-targeted species. For now eradication remains a dangerous procedure, but perhaps in future it will become a safer bet.

Over and out

The Invader Inspector

P.S. Thanks to Isabela DePedro and Daniel Hamilton for linking me to the Parks and Panetta and Marris papers. I highly recommend checking out both of their blogs too.

Managing Invasive Species: An Introduction

Today's topic is incredibly broad. As we've seen already, invasive species include multiple types of flora and fauna and can have positive or negative impacts upon a wide range of ecosystems. Their arrival can both initiate, and be initiated by, environmental change.  As such the range of management techniques is also rather broad.

To try and cover everything would require a thesis and sorry but ain't nobody got time for that. Instead, I'm going to dedicate the next few blog pieces to management in an attempt to give the topic the depth of attention it deserves. Today I'm just going to provide a brief introduction.

Probably best to begin with a definition of the key term for the next few weeks. The Oxford English Dictionary defines management as:

 

Organization, supervision, or direction; the application of skill or care in the manipulation, use, treatment, or control (of a thing or person), or in the conduct of something.

Vague much? There's rather a lot of 'or's in there.

This is matched by management in relation to invasive species. I'd imagine conversations on the topic go something like :

Chairperson: 'Well those >insert invasive species here< are a pain aren't they? What should we do?'
Person 1: 'KILL THEM, KILL THEM ALL'
Person 2; 'Or, we should just introduce some kind of legal framework to prevent their spread'
Person 3: 'Or, we need to just let nature manage itself'
Person 1: 'SHUT IT YOU HIPPY, I'M GETTING MY GUN'
Person 4: 'Or how about we just carefully monitor them and introduce preventions to the spread?'
etc

My mental image of Person 1, he can't wait to get out there and shoot some invasive wabbits

There's often little agreement about what constitutes appropriate management, with some preferring caution and others opting for novelty (Larson et al., 2013) and options ranging from complete eradication to tolerance of 'new' species as an enrichment of local biodiversity (Walther et al., 2009).

So, lots of options to cover and I'm going to start with eradication next time. Let's see if I can manage to do it justice.

Over and out

The Invader Inspector

The Invasive Snail Helping Kites Soar

Following up from my piece a couple of days ago on whether or not invasive species facilitated the decline of certain bird species I came across this interesting article covering the opposite impact.

The piece documents the resurgence of the previously endangered Floridian snail kite (Rostrhamus sociabilis) thanks to feeding on invasive apple snails (Pomacea insularum), which themselves feed on the invasive plant hydrilla. 

A snail kite, wonder how it gets its name?...

Maybe something to do with these guys, the invasive apple snails that the snail kite feasts upon

According to bird expert and ecologist, Wiley Kitchens, four years ago the snail kite was in 'dire straits' (not the band, though I hear snail kites enjoy Wings) and 'looking at almost an eminent extinction'. However, the snail kite now takes great advantage of the 'explosive' (sic) expansion of an exotic species.

Kite numbers were at 3400 in 1999, before crashing to only 650 in 2009. Today they have recovered to about 1200. Kitchens describes this as 'a monumental turn-around ecologically'. 

So, maybe the title and conclusion previous piece were unfair. Sometimes invaders aren't implicated in species declines at all. In fact, the situation can be quite the opposite. 

Over and out

The Invader Inspector

Invasive Species: Passengers Or Drivers Of Native Declines?

Today I've decided to investigate a real doozy of an ecological question: whether or not invasive species actually cause the decline of natives or if other factors, such as habitat degradation, are responsible. 

Also, I've really enjoyed reading the blog Goodbye,birdsong?, so I thought inspecting invaders should also give some due attention to our feathered friends (wouldn't want any RSPB members to get in a flutter). 

And I'm doing it the style of a police report. I miss my past life sometimes...

CASE REPORT

The Question: Are invasive species drivers of native species decline or passengers of habitat modification? 

The Case: The impact of the invasive common myna (Acridotheres tristis) on native bird species. (Specifically, is the common myna impacting native species or is it down to forest density?)

Chirpy chappy: The common myna

Location: Canberra, Australia. 

No they aren't random cat heads, they're the distribution of the common myna in 1900-81 (left) and 1998-2000 (right), highlighting its territorial expansion.

Prior knowledge: Habitat modification and invasive species play significant roles with regard to the state of biodiversity. However, distinguishing between the two is often difficult. This is referred to as the 'driver-passenger' model ('passengers' take advantage of habitat modification whereas 'drivers' actually cause native species declines). 

The common myna is 1 of only 3 birds in the IUCNs 100 of the worst invasive species list (Lowe et al., 2000). Concern that it displaces natives through competitive territorial dominance, however, evidenced is mixed. 

Gurevitch and Padilla (2004): Native species impacts can result from invaders directly or compounded by a modified habitat. Research often investigates the anthropogenic habitat impacts or the effect of invaders on natives. This means drivers of change could be mistakenly identified.

Hypothesis: Common myna is both a passenger of habitat change and a driver of some native bird declines.  

The Evidence: Collected by Grarock et al., 2013 in a 2.5 year study investigating changes in native bird abundance in relation to different habitat types and common myna abundance. 

Illustration of the different habitats considered in the study.

Results: 

• Significant relationships uncovered between common myna abundance and tree density. Abundance declines as tree density increases.This suggests that the common myna is a passenger of habitat change.
• No significant relationship found between common myna abundance and total species richness, which is strange as invasive species normally dominate over native species. 
• However, there is a negative relationship between common myna abundance and the gang-gang cockatoo (Callocephalon fimbriatum), potentially driving its decline. 8/20 native small birds shown to be negatively impacted by the common myna. 
• Significant positive relationship between common myna abundance and large bird abundance, but not effect on species richness.

  

  Goodbye gang-gang? The common myna is implicated in its decline.

Key Findings:

1. The common myna is a passenger of habitat change.
2. In combination with habitat change, the common myna appeared to be a driver of some bird species declines.
3. It is essential to simultaneously investigate invasive species impact and habitat modification to assist with differentiating the impacts on natives.

Discussion points:

• Study not comprehensive, it does not include potential influence of other species. Acknowledged that it would be difficult to account for more complex ecological interactions.
• Fragmentation of native vegetation and reduced tree density may enhance habitat quality for the common myna, enabling the species to spread to new areas and compete with natives. This could be relevant to countries such as Madagascar, Indonesia and other countries experiencing deforestation in the presence of the common myna.  

Conclusions:

Results suggest impacts of habitat modification and invasive species are interrelated. Many species are strongly influenced by habitat, however, not all species appreciate the same habitat conditions. Both factors can substantially impact native taxa. It would be wrong to say either one is more important in causing declines as each species should be treated uniquely with regard to the threats it faces. 

Sorry for a cop-out, fence sitting conclusion, but I feel it's the most appropriate one. Are invaders drivers or passengers? The answer would have to be that they can be both. Case closed.

Over and out

The Invader Inspector