Removing invasive species

Whether it involves the use of chemical treatment, physically uprooting plants, or introducing biological controls, there are numbers projects in place to remove invasive species e.g.1, 2, 3. However, invasives are persistent and removal is expensive (Pimentel et al., 2000) so should not be done light heartedly. I found it particularly interesting that removing invasives may also have unexpected ecosystem wide effects (Zavaleta et al., 2001).

Macquarie Island is a natural heritage site, home to a variety of native plant species and seabird colonies. The story of what happened on this Island describes what can wrong if conservationists do not consider ecosystem processes and food web structure before removing invasive species…

Cats were unfortunately introduced to the island in the early 1800’s and rabbits were later introduced by sealing gangs in 1878. When the rabbits arrived they were preyed on by the cats and populations were kept at equilibrium. Despite this the population size was still large enough that rabbit grazing activity had an extremely negative impact on the vegetation. As a result the European Rabbit Flea was introduced to the island to further reduce the rabbit population and protect the native vegetation. The flea was effective and the population size decreased. However, the conservationists did not consider the implications that this would have on the cats, which developed an appetite for seabirds in the absence of rabbits! In response to this the cats were shot on the island, which obviously lead to an increase in rabbits! (Bergstrom et al., 2009)

This is not the only case where eradication has been hard. The Giant African Snail recently featured on BBC News for this exact reason. 

For those of you against invasives it therefore seems that prevention is more beneficial than eradication. Methods of preventing invasives can be read about here, and interestingly investment in prevention could save money in the long term (Leung et al., 2002)

This adds to the debate of whether or not we should allow invasive species that are moving north as a consequence of human induced climate change to establish or not. After all, invasive species can have a positive effect on the environment, but if we don't prevent them will it be too late to find out?

In the new year I’ll be posting my opinion on invasive species and climate change – in the mean time have a fabulous time celebrating the start of 2014!

Elena

Aliens Vs Climate Change

Could invasive species be driven by climate change?

In 2006 a team of scientists studied the distribution of terrestrial and aquatic organisms in Great Britain between 1960-2000. The researchers found that 12 of the 16 taxonomic groups studied shifted their range to high latitudes or altitudes (Hickling et al., 2006). Hickling et al., (2006) reasoned that during this period global warming was occurring and was likely to be a factor driving changes in species range.  More recently, a meta-analysis has been published revealing that species are migrating north of the equator at an average rate of 16.9 km per decade, or to a higher elevation at a rate of 11 m per decade (Chen et al., 2011). This is at least twice as fast as was previously predicted. Moreover, Chen et al. (2011) provided statistical evidence that these rates of migration are correlated to temperature change, indicating a direct link between species migration and climate change. 

Why move north? 

Generally speaking, as you move north or south of the equator there is a decline in temperature, similarly at higher altitudes the temperature cools. In other words, the warmest temperatures that put populations under the highest level of stress are nearer the equator. Adaptation to climatic stress takes place over many generations and if species cannot evolve fast enough then global warming may result in population crashes (Pounds et al., 1999). 

The Edith's Checkerspot is a particularly well studied butterfly species which excellently represents this change in geographic range over time. Parmesan (1996) found that net extinctions were greater for populations at lower latitudes than at higher latitudes (Fig. 1). This extinction gradient is what was expected if climate change was causing the range shift, as populations closer to the equator suffer from hotter temperatures. 

Figure 1. Left: Edith's Checkerspot. Photo credit: H. Stroo.
Right: Map of Edith's Checkerspot populations monitored between 1992-1996. Red indicates extinct populations. Blue indicates present populations (Parmesan, 1996)

Previously I defined invasive alien species as those that are introduced to a new environment and have a negative effect. Therefore if migrating species compete with exiting communities, climate change has the potential to directly facilitate the introduction of invasives! 

Until now attributing the cause of invasives to either human activity or natural change has been fairly straight forward. Climate change poses a slightly harder question. I think that the findings from the Firth Assessment Report by the Intergovernmental Panel on Climate Change (IPCC) are critical to this debate. Although climate change is affected by natural internal variation, one of the key focuses in this report was the increased certainty that humans are the main cause of recent global warming (Fig. 2). 

Figure 2. IPCC (2013)

With this in mind I'll leave you with one final thought. Do we have the right to prevent species from naturally migrating and invading new locations in order to survive global warming when humans are the dominant cause? If we are currently experiencing a 6th major extinction (Barnosky et al., 2011), should we in fact be letting these species establish in new ranges if it minimises the total number of species extinctions?

Until next time!
Elena 

Ecosystem Services

In my last post I mentioned ecosystem services; as a slight aside I thought you might be interested in this video which outlines the key ecosystem services. Hank Green puts particular emphasis on the human impact to ecosystem services as a result of biodiversity change. Whilst watching the video it's worth bearing in mind the effect that invasives had on the ecosystem services of South Africa - there are lots of similarities. Keep your eye out for the reference to invasive species towards the end of the video! 

Positive potential

It's time to take a more optimistic approach, and look at the positive effects that invasive species can potentially have on ecosystems. I’ll start by proposing counter-arguments for the 3 problems described in ‘Why the bad press’. 

1. Predation
Let’s take a look at the European Green Crab, which was a successful invader to America at locations where the native predator (Blue Crab) had been removed as a result of human activity. Due to the local extinction of Blue Crabs, the population of an herbivorous crab species lower down the food chain dramatically increased. This herbivore was able to strip salt marshes of hundreds of hectors of vegetation, namely cordgrass, which resulted in salt marsh die-off and impacted negatively on the ecosystem. The invasion of the Green Crab is thought to have significantly reduced the population of the herbivorous crab via predation. Optimistically there was found to be a positive correlation with Green crab abundance and cordgrass recovery. (Bertness and Coverdale, 2013)

2. Competition

When an invasive species expands its geographic range, it competes for resources with pre-existing species. If some native individuals are able to survive, then invasives may drive the evolution of these native species and select for traits which increase fitness. Ferrero-Serrano et al., (2009) found this to be true for native grass populations. The authors demonstrated that as a consequence of previous competition imposed by invaders, evolved species were more likely to be able to tolerate new invaders. Importantly the authors argue that this knowledge may help advance the understanding and practice of restoration ecology. 

3. Disease

Ok so this one was a little bit harder….even after trawling the internet I have failed to come up with a valid argument! 

To compensate I have found a case study to share with you that I thought was particularly interesting. Pejchar and Mooney (2009) reviewed whether different ecosystem services in South Africa were positively or negatively impacted on by the invasion of woody plant species.

(Pejchar and Mooney, 2009)

This review by Pejchar and Mooney (2009) highlights just how many ecosystem services invasive species can affect. Moreover, there is only one ecosystem service where invasive species had a strictly positive influence. Whilst reading the literature in preparation for this blog post I found that this was often the case. As a result I am personally still not swayed; to me it seems evident that invasive species have a net negative effect.

Let me know what you think!

Elena 

Christmas Spirit!

In order to spread some festive cheer, the Metropolitan Arroyo Flood Control Authority (MAFCA) of Albuquerque, New Mexico, has got creative with one particular invasive species. Tumble weed, perhaps more famous for its roll in western cowboy movies, is now under the spotlight for a different reason! For the past 15 years a tumbleweed snowman has featured along Interstate 40, reaching a very respectable height of 13 ft. in 2012 (National Geographic).

Photo credit: D. Cook and L. Jenshel (National Geographic)

Currently New Mexico is not predicted to experience white Christmas this year, so why is tumbleweed such a super replacement?

Tumble weed is a generic name for a number of plant species however, Russian Thistle is the species that is likely to be at the heart of the MAFCA snowman. This species was first introduced in 1873 by Russian immigrants (Orloff et al., 2008). As tumble weed ages throughout the year its stem becomes increasingly brittle and decreases in flexibility until it finally snaps. It was a successful invader as its spherical shape not only makes it perfect for creating a snowman silhouette, but also for rolling in the wind! The distance tumble weed can travel is highly dependent on wind velocity, and has been found to travel up to 4069m from the original location (Stallings et al., 1995). This enables rapid seed dispersal over a very wide geographic range, making it a great invader! Until it hits a physical barrier it is practically unstoppable! Here's a photo where tumble weed has been allowed to accumulate out of control...                      

Photo Credit: D. Cook and L. Jenshel (National Geographic)

Despite providing a wonderful structure for the Interstate 40 snowman, it should be noted that Russian Thistle can also have a negative effect on the environment, particularly as it acts as a fire hazard. Consequently emphasis has been placed on trying to keep population size to a minimum - you can read about some of the management processes here. Whilst constructing the snowman, MAFCA may well be alerted to areas of high Russian Thistle concentration, which can then be delt with in the appropriate manner. 

I want to leave you with the consideration that this invasive species creates great excitement among the daily commuters of New Mexico. Although this positive effect is not related to the environment, could it be possible that not all invasive species are bad? I'll be following this post up with a more scientific debate!

In the meantime, I hope you're getting into the festive spirit as much the population of New Mexico!

Elena

Survival Guide

From Camley Street Nature Park to the Arctic, it seems that invasive species have the potential to crop up just about everywhere! But what is it about these species that allows them to become so well established in the new locations across the globe? I've combined the traits of some of the top invaders to create the ultimate invasive species survival guide...

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Invasive Species Survival Guide

1. Climate Matching

Species that are introduced to a location where the environmental conditions are similar to that of their native range may be more likely to succeed (Bomford et al., 2005). This is as their physiological adaptations and behavioural responses are already suited to seasonal variations in temperature, precipitation.  

2. High competitive Ability

Species with a high competitive ability such as the Argentine ant (Holway, 1999) are more likely to acquire food, water and habitat resources that are necessary in order to survive.

3. High intrinsic rate of increase
The intrinsic rate of increase takes into consideration the number of surviving reproductive individuals, the proportion of these which are females, and the age at which females can reproduce. Thus the higher the intrinsic rate of increase, the more rapid population growth is. As a result, species that have a high intrinsic rate of increase are more likely to be successful invaders (Crawley et al., 1986).

4. High abundance in native range

Firn et al., (2011) studied the abundance of invasive plant species in their native and invasive range across eight countries, revealing that there was often a similar abundance in both locations. This suggests that if a species is very abundant in its native range it is likely to be abundant in its invasive range.

5. Availability of suitable habitat and vacant niche

Due to an increased availability of resources, a vacant niche means that an invasive species is more likely to become established in a new location. For example, ant species with different sized mandibles consume different sized food sources; allowing the species to be separated dependant on their food niche. Arndt (2006) showed that when the food niche was empty, species were successful invaders. However, when ants were introduced to a site where their niche was already occupied by an existing species, the invader did not establish.

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*Terms & Conditions:

To succeed as an invasive species not all traits are necessary (Daehler, 2003; Gallagher et al., 2010) however, a combination of multiple traits can be advantageous!  

The Polar Express!

The global effects of climate change have become a prevalent issue in the 21^st century. The Arctic ocean is currently warming rapidly (Somavilla et al., 2013), and due to Arctic amplification this region is set to experience a particularly high level of warming in the future (IPCC, 2013). As a result the Arctic has been a key focus of climate change research, with particular emphasis being placed on September sea ice extent. Sea ice extent is important during this month as it reaches an annual minima. Since the 1980s the annual sea ice extent has declined rapidly (IPCC, 2013) (Figure 1).  

Figure 1: Annual sea ice extent (IPCC, 2013)

This week I came across a recently published paper suggesting that Trans-Arctic shipping routes may directly be affected as sea ice extent continues to reach record lows. Smith and Stephenson (2013) used general circulation models to predict the sea ice extent across the Arctic under different emission scenarios. They then applied this to the Arctic Transportation Accessibility Model in order to calculate the fastest route that ships could navigate between the North Atlantic and the Bering Strait. Interestingly Smith and Stephenson (2013) predict that by 2050, ships equipped with appropriate ice-protecting mechanisms will be able to navigate across the North Pole during the summer months (Figure 2). 

Figure 2: New shipping route for Polar Class 6 vessels indicated in red (Smith and Stephenson, 2013). 

Despite the economic benefit of shortening the transportation time, there are concerns about the novel route among conservationists. Crossing the North Pole provides a new opportunity for the spread of invasive species such as mosquitoes, mussels and barnacles, via ballast water and cargo transportation (Palmer, 2013).  

Research suggests that some invasive vascular plant species are already capable of surviving in the Arctic under current climate conditions (Ware et al., 2011). With increased opportunity for invasive species to be introduced, it is likely that these populations will thrive. Additionally as the Arctic ocean warms, conditions are likely to become more favourable for the survival of a wider variety of invasive species (Ware et al., 2013). Scientists are yet to fully understand the impact that invasive species may have on the Arctic region however,  evidence from previous species introductions around the globe suggests that it may dramatically alter the ecosystem. 

Here I have just touched on one way in which climate change will effect the Arctic ecosystem. If you would like to learn about how declining sea ice extent may also have a dramatic effect on Polar Bear populations, then I recommend reading Larissa's Post "Snowball effect: Climate Change and Polar Bear Population Dynamics"

That's all for now!
Elena