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

Invaders Must Die? The Prodigy Vs The Ecology

It's Friday, so I'm forgoing today's piece in favour of having a rave.

Over and out

The Invader Inspector

Ok not really... but I need to check something. Are you feeling pumped? Are you? Because if not then you should be. Today we are turning the tables, ripping up the rulebook and other analogies for looking alternative viewpoints.

Because today, we're looking at positive impacts that invasive species can have!

Did you see that coming? You should have because I said it was going to happen in the quiz. (Which, incidentally, Endemol have expressed an interest in. They think it could be the new Deal or No Deal). 

So far we've only really looked at negative impacts of invasive species (remember those poor red squirrels? REMEMBER THEM?!?!). and I'm all in favour of trying to cover multiple angles. I mean this blog isn't for propaganda...

No place for propaganda here (and yes I succumbed to this terrible trend. And yes, that is a dog #ashamed)

Yet...

Before addressing some studies, I decided to do a crude bit of data collection myself. I searched Google Scholar for: 'invasive species negative impact' and 'invasive species positive impact'. Results are in the table below.

	All time	Since 2013
Invasive species negative impact	427,000	17,500
Invasive species positive impact	385,000	17,300

To summarise, in all time search results 'negative' comes up with approximately 10.9% more results than 'positive'. BUT since the start of 2013, the difference is only 1.10%. Hardly the most extensive data analysis ever undertaken, but it seems to indicate an increasing awareness that invaders can also have a positive impact.

So, what are those positive impacts?

Well, McLaughlin et al (2013) examined the ecosystem function and service impact of what Vila et al (2010) identified as the 10 'worst' European invasive species. The study found that negative impacts of invasive species are often assumed rather than evidenced quantitatively (!!!!) and shows that some invasive species are covered far more often in literature than others.

The ten 'worst' invasive species in Europe and their total no. of articles retrieved from ISI web of knowledge.

The paper also examined provisioning, regulatory and cultural ecosystem services. Out of 11 services examined, the 10 invasive species were shown to impact all but one of them (climate and air quality), mostly in a variety of ways. Only Balanus improvisus (the Bay barnacle) and Branta canadensis (The Canada Goose) were shown to have no positive impact, so Justin Bieber isn't alone in his category as a Canadian pest.

All impacted services had mixed results apart from new products/ industries from biodiversity (only positive) and regulation of floods and fires (only negative). Full results of McLaughlin et al's study are summarised in the table below.

Summary of impacts of 10 worst invasive species according to literature. Key: Black = -ve impact only. Grey = +ve and -ve impacts. Diagonal lines = +ve only. (IMHO being able to read this >> being outside my margins)

Clawing out the specific case of Procambarus clarkii (the freshwater crayfish) reveals a multitude of complex positive and negative impacts. The crayfish can be farmed or caught by fisherman, which can generate income. However, farming costs could outweigh benefits as they can cause physical damage to the habitat.

Their impact on trophic pathways is also mixed. Many large predators consume P. clarkii, reducing the ecosystem's number of trophic levels, leaving it more vulnerable to an abrupt change of state. However, at the same time, by providing a food source to higher predators, a positive effect is realised with regard to several birds of high conservation value.

Procambarus clarkii : its presence puts us in a bit of a pinch

As my extensive data collection suggested, the study of invasive species' positive effects is indeed receiving increasing attention. However, an issue precluding this is that invasion ecologists often present significant subjectivity and emotive reasoning against invasive species in literature (see Schlaepfer et al., 2013 first paragraph in particular).

Given the fact that invasive species can have positive impacts, I view this lack of objectivity as unprofessional. Invasive species can act as ecosystem engineers, boost vital services like pollination and restore ecosystem functions that were previously provided by another species, subsequently lost to habitat change.

An example of this is ecological restoration of the degraded Cape Cod salt marshes in New England, U.S.A. by an invader (Bertness and Coverdale, 2013). Overfishing (human activity again...) depleted salt marsh predators and allowed Sesarma reticulatum (a herbivorous crab) to denude hundreds of hectares of low marsh. However, an invasion of carnivorous Carnicus maenas (green crabs) into the marshes partially reversed decades of cordgrass die off, either by consuming the herbivorous crab or evicting it from its burrows, thus reducing herbivory and promoting cord grass recovery.

(A) Regression analysis of Carnicus abundance and cordgrass recovery demonstrating a positive correlation and that Carnicus denisty explained 37% of inter-site variation in cordgrass regrowth. (B) Carnicus presence significantly reduced Sesema burrow usage, rendering it more vulnerable to predation and desiccation.

Conversely, invasive plants can also have positive effects for an ecosystem's animals. For example, Malo et al. (2013) report that the invasive shrub Rhododendron ponticum, can have a positive effect on Apodemus sylvaticus (wood mouse) abundance in Southern England, primarily by providing a 'shield' from aerial predators.

A cute little wood mouse, where's a Rhododendron at when you need one?

Wood mice play an important role in many terrestrial ecosystems as they disperse seeds and act as a staple prey for numerous predators, whose breeding success is affected by changes in rodent density (King, 1985). However, rodents can have negative effects on agriculture (Stenseth et al., 2003) and pose a human threat by spreading disease. Hence, once again, positive effects are present but there are still negatives too.

To conclude, it seems that sometimes we, including professional ecologists, can be too quick to write off invasive species as only having negative impacts. In reality the ecological picture is, as always, much more complex and a lot of the time we lack sufficient data to know precisely what is going on.

For this to even become remotely possible, I think it is imperative that subjectivity is removed from research on the matter and not let the more obvious negative impacts overshadow the positives. Overall, we would be very wrong to say 'invaders must die', which just goes to show, when it comes to ecology, you shouldn't take advice from musicians.

Over and out

The Invader Inspector