Invasive freshwater fish (Leuciscus leuciscus) acts as a sink for a parasite of native brown trout Salmo trutta (2020) Tierney et al. Biological Invasions. Read it here.
From house cats to cane toads, invasive species are one of the biggest threats to native plants and wildlife, second only to habitat destruction. An invasive species is a living organism that is a) introduced by humans from its native range to an area it doesn’t naturally occur, b) spreads and forms new populations and c) causes some kind of damage to the native ecosystem, economy or human health. Current lockdown conditions notwithstanding, introductions of invasive species have become increasingly common in our globalised world with easier travel and trade between countries. The spread of invasive species creates new ecological interactions between native and invasive species that can impact how our native ecosystems function, including disease dynamics. If the development and transmission of native parasites is different in invasive hosts compared to their usual native hosts, the parasite dynamics of the whole system can be altered.
This past August, I was lucky
enough to visit the Galapagos Islands during my travels through South America.
My visit here was quite possibly the highlight of my trip, with plenty to keep
me thoroughly engrossed.
Set some 1000 km off the coast of South America, the Galapagos Islands were first stumbled upon by Tomas de Berlanga in 1535 when his ship was blown off course during a voyage between Panama and Peru. It was almost three hundred years later before the first human briefly settled on the islands, in 1807. However, this was due more to necessity than desire, as the settler in question was marooned on the islands. The islands were eventually made famous by Charles Darwin, who visited aboard the HMS Beagle in 1835, and used his observations of the island species as the basis for his “Origin of Species”.
An array of some of the commonly sighted species in the Galapagos: a blue-footed booby rests in the foreground with a juvenile marine iguana to its right. Behind it are a Galapagos penguin and a Sally lightfoot crab. Continue reading “The Galapagos Islands: paradise lost?”
The River Shannon is Ireland’s largest river, with a storied biological and cultural history. The River drains 20% of the country, running through the centre of the midlands while providing a source of power and water. The machinery used to generate power in most power plants, whether they’re nuclear, peat-fueled, or coal-powered plants, often heats up to extreme temperatures when the plants are running. To try to keep the machinery cool, many power plants today take water from local sources, use it to cool the generators, and then put it back out into the original source. Two of Ireland’s largest power plants, the Lough Ree Power Station and the West Offaly Power Station, use water from the River Shannon in this way, putting the water back into the river up to 10°C hotter than the River water. The warm water can change the structure of the aquatic community near the output, and our study shows that this increase in temperature gives a significant boost to the invasive Asian clam, Corbiculafluminea.
Every year, the Trinity College Dublin Zoology, Botany, and Environmental Science moderatorship students (final year undergraduates) complete their own research projects related to their course. It has been my absolute privilege to spend time with these talented students and to watch their projects take shape. I am blown away by the dedication they show, the incredible topics they cover, and the way in which they approach their investigations. After their theses are submitted, the students hold a poster session where they present their work. From beetles to beer and back again, this year’s students have done impressive and solid work. I hope all our readers enjoy learning about these projects as much as I did! If you’d like to contact any of these students to congratulate them, offer them prizes/jobs, or learn more about their projects, most of them have included contact information. Without further ado, I’ll let them take it away! -Maureen Williams, PhD Student, Zoology
As mentioned previously on the blog, Andrew Jackson and I started a new module this year called “Research Comprehension”. The module revolves around our Evolutionary Biology and Ecology seminar series and the continuous assessment for the module is in the form of blog posts discussing these seminars. We posted a selection of these earlier in the term, but now that the students have had their final degree marks we wanted to post the blogs with the best marks. This means there are more blog posts for some seminars than for others, though we’ve avoided reposting anything we’ve posted previously. We hope you enjoy reading them, and of course congratulations to all the students of the class of 2014! – Natalie
Here’s views from Sharon Matthews on Dr. Amy Pedersen‘s seminar, “A systems ecology approach to infection and immunity in the wild” and Dermot McMorrough’s take on Professor Christine Maggs‘ seminar, “Invasive seaweeds and other marine organisms”.
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It’s a ‘wormy’ world we live
Sharon Matthews
We all walk around thinking I will never have parasites but apparently our chances of becoming infected are high because there are around 1,400 species of parasite that can infect humans. If this news wasn’t bad enough, Dr. Amy Pederson informed us at her seminar that our chances of becoming infected with two or more parasites at the same time, is also very high. Dr. Pederson explained that through her work, she hopes to understand the phenomenon of co-infection and the interactions between these parasites in a host that drive this trend.
Dr. Pederson and colleagues showed through a meta-analysis of studies that co-infection is often associated with higher parasite abundance and a negative effect on human health. The interspecific interactions between parasites in a host can influence disease severity and transmission through the immunological responses of the host, making an environment more accessible for another species.
To investigate this phenomenon, Dr. Pederson chose to do a perturbation study using the wild species of wood mouse, Apodemus sylvaticus as a host system. A lot of past studies on parasitism have used a laboratory mouse model because of accessibility to the subject and ease of manipulation and control of confounding factors. I think it is very important to also have wild animal model systems because they strongly represent the variation and dynamics that would be seen in a real-life infection scenario. Also the wood mouse can be parasitised by 30 different species (both micro and macro parasites) and up to 70% of them can be co-infected which resembles the situation in humans.
Dr. Pederson wanted to determine the nature of the interactions among the parasite community in the woodmouse and to assess the stability of the community so she used the anthelminthic drug ivermectin to perturb the system. This drug targets nematodes, the most abundant member of this community so interactions between these and other groups should be apparent from perturbing their numbers. I liked the fact there was a longitudinal aspect to the experimental design as it allowed the effects on the parasite community to be analysed over time. All of the wood mice were tagged at the beginning and there were 3 different treatment groups: controls that received water at every monthly capture, a single treatment group and a group that received treatment of ivermectin at every capture. Faecal and blood samples were taken at each capture to check for levels of infection through egg counts and blood smears.
The results showed that treated mice had a 71% lower probability of infection 3 weeks after treatment than control mice but no difference was seen after one to two months because nematode numbers increased. This suggests that the effect on nematodes was short-lived and the community of parasites was resilient, returning to the original state before perturbation. This pattern for reduction and then returning to normal levels of infection was seen in Heligmosomoides polygyrus, the most abundant nematode in the community. This parasite shares an infection site with the protist, Eimeria hungaryensis. As the numbers of H. polygyrus reduced, the numbers of E. hungayensis increased and then returned to original levels once H. polygyrus recovered. This effect on a non-target species suggests that there may be a competitive interaction between the two species. They both occupy the same niche in the gastrointestinal tract of the wood mouse and reduction of numbers of the more dominant nematode may have given the protozoan a chance to use resources not normally available to it to colonise. No treatment effect was seen on any of the other parasite species.
The work of Dr. Pederson is very interesting and it gives us a window into the dynamics underlying co-infection. This work will broaden our understanding of the world of parasites and how they interact and will help inform us in our choice of treatment and which species may be effected by it. The one thing I was happy about coming out of the seminar was the fact that Dr. Pederson said, “those who are wormy usually remain wormy”. In other words, individuals with high burdens of nematodes (worms) show a tendency for reinfection over time. That leaves me with some hope that for at least now, I remain wormless and if the stats are anything to go by, I have a chance at remaining wormless for the forseeable future.
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Review of Christine Maggs’ seminar
Dermott McMorrough
The effect of invasive species is, by now, well documented and is often brought to light when species’ such as grey squirrels, American crayfish, zebra mussels, and Japanese knotweed turn up in a new environment; an event all to familiar to ecologists. Those listed above are just some of the examples of ‘alien’ species known to kill off native creatures and plants when they become established in new habitats. In Ireland, for example, the role of the North American Grey Squirrel has been well studied due to the effect they have had on our native Red Squirrel since their introduction into Co. Longford in 1911.
Invasive species have an incredible ability to migrate and establish themselves thousands of miles from their origin, either organically, or often with a helping hand from humans for example by hitching a ride as stowaways on trade ships or in ballast tanks, as has been the case with Zebra Mussels. The shared ability of the aforementioned species to colonise vast areas is no mere coincidence. Several species are introduced to new ecosystems, accidentally or otherwise, but relatively few have enjoyed such enduring success. Aside from threatening native species of plants and wildlife, the incredible growth of these species can lead to them negatively impacting on anthropogenic activities, whether it be fouling mooring lines or clogging water intake pipes as has been the case at the Guinness brewery at St. James’ Gate.
Professor Maggs’ seminar began with an explanation of how an invasive species can colonise an area. While her background was evidently in Botany, she made a particular effort to appeal to the zoologists in the audience with numerous references to the role of oysters in the spread of macro algae. Her research covers a fairly broad area, and pinpointing an exact research question has eluded many in the room. We were, however, treated to a synopsis of how invasives go about establishing themselves, and the methods often employed to prevent this process or eradicate it if it has already taken place. For example, methods such as immersing oysters in concentrated brine or flash boiling them have proven effective in fighting the spread of invasive algae, which use the oysters as a vector.
The spread of an invasive alga would not seem like an immediately worrying problem to those untrained in ecology. As with many problems in science, it is not until the issue directly affects the people in charge of policy making that anything is done to rectify it. This unfortunate criterion was evident in one of the examples used by Professor Maggs. In 2008, the city of Qingdao was due to host the Sailing event of the 29th Olympic games, but just weeks before racing was due to start, an algal bloom covered Qingdao bay in a thick layer of Enteromorpha algae. The presence and strength of the bloom was largely accredited to the high levels of nitrates in the water as a result of farmland runoff, coupled with higher than average temperatures and rainfall. During the seminar, the use of giant plastic sheets in San Diego Bay was seen as an American answer to an ecological problem, but it worked. Credit where credit is due. The imminent deadline of the Olympiad prompted the Chinese authorities to tackle this ecological disaster with what has to be the most wonderfully Chinese way possible: by ordering 20,000 locals to line the beaches, and man over 1,000 fishing boats to rake in the bloom manually. Sure enough, within a few days over 100,000 tonnes of the algae had been shipped out of the bay.
Increases in the amount of travelling done by humans and more importantly freight over the past century has led to an explosion in the ranges of successful invasive species, to the point at which one must wonder how endemic species can survive at all? The increased efficiency of our transit routes has also meant that invasives no longer rely on miracle migrations, such as that likely undertaken by the Iguana of the Galapagos. With the ever-increasing demand for fresh exotic produce in the developed world, the ships are getting faster, the coolers are getting colder, and the chances of an invasive species making it’s way around the world in less than 24 hours, perfectly preserved in Tesco wrapping and ready to colonise a new ecosystem have been made just that much easier. It seems that when it comes to being an invasive species, every little helps.
There are many threats to our environmental security: climate change, habitat loss and degradation, pollution. All are damaging the environment and impacting on our long-term survival. One threat that seems to have been often overlooked by the public, however, is the effect of invasive species.
Invasive species are non-native species that adversely affect the invaded region. Not every non-native species becomes invasive: some fail to establish while others may establish but at sufficiently low population densities to have minimal impact on their new home. But a few species will find themselves so at home in their new land that their populations explode and, due to a lack of any predators adapted to deal with them, their populations remain unchecked.
There are many famous examples of invasive species: the Burmese python in Florida, rabbits and cane toads in Australia, the grey squirrel in the UK and Ireland. Attempts to control all these species have been made over the years, though none have successfully managed to completely eradicate them.
Invasive rabbits!
While much of the media is focused on local invasive species, the greatest impacts are often found not in large inhabited countries but on small, isolated islands. You may be wondering how invasive species can reach small, isolated islands but humankind’s reach has been vast and in the days of shipwrecks and long voyages sailors often found themselves on shores never-before touched by man. When they came ashore so too did stowaways in the form of rats. Some species were even purposefully introduced in order to provide food for victims of shipwrecks. In these ways species including rats, cats, rabbits, pigs, sheep and reindeer have found their way to islands all around the world, including those in the sub-Antarctic.
The impacts of these species have been great and varied. Many islands are home to ground-nesting seabirds and their eggs and chicks are extremely vulnerable to predation by rats and cats while their nesting sites can be damaged by rabbits and larger mammals. Grazing also impacts on the islands, leading to habitat loss and soil erosion. As seabird numbers have fallen due to interactions with fishing gear, harvesting for food and though the effects of invasive species on their breeding success, attempts have been made to rid islands of these now unwelcome interlopers.
The effects have been mixed. Some attempts have been hugely successful. The most successful is arguably that of Campbell Island, a sub-Antarctic island south of New Zealand. It had a succession of eradications starting in the 1980s that culminated in the early 2000s with the eradication of rats across the entirety of its 113 square kilometres. This was at the time the largest area ever cleared of rats. I remember being told by a lecturer, though this may be apocryphal, that there was a conference going on at the time where people were explaining why it was impossible to eradicate rats from large islands at the very same time that this eradication programme was coming to a successful close.
Campbell Island
Some attempts have not been so successful and they highlight the importance of good management and understanding of food web interactions. I believe, or at least I certainly hope, that the following example is the most extreme case to date. Without further ado, I present to you the case of Macquarie Island.
Macquarie Island is a sub-Antarctic island between Australia and New Zealand. It is home to elephant seals, three species of fur seal and thirteen species of seabirds including penguins, petrels and albatrosses. Rats, mice and cats were introduced by sealers in the early 1800s and rabbits were introduced in the 1870s. Both the cats and the rabbits have had devastating impacts on the seabird colonies. Rabbits caused erosion through their burrowing and cropping of the vegetation while the rats ate young chicks. The combination of predation and habitat destruction are thought to be responsible for extinction of the two endemic species on the island, the Macquarie Island parakeet and the Macquarie Island rail.
Macquarie Island
By the 1980s the habitat destruction was becoming significant and a decision was made to control the rabbits through the introduction of myxomatosis which decimated the rabbit population. This had an unexpected impact on the cats: it turned out the cats had been predating on the rabbits and used them as their main food source so when the rabbits disappeared the cats turned their attention to seabird chicks. Once this was realised the need to control the cat population was quickly recognised.
A cat eradication programme began in 1985 and by 1999 the last cat on the island was killed. You would be forgiven for thinking that this is the end of the story: rabbits controlled, cats switched their diet, the mistake is recognised, cats are controlled, and now the seabirds can live happily ever after. . . If only it were that simple.
The rabbit population began to re-establish itself. It increased rapidly and by 2006 was back to pre-control levels. The rabbits were devastating the island In 2006 a large landslip, caused by erosion by rabbits, partly destroyed a penguin colony.
It was clear that something had to be done and in 2007 the Australian Government announced their intention to eradicate Macquarie of invasive rabbits and rodents (rats and mice) at a cost of A$25 million. The need for this eradication was highlighted in a 2009 paper by Dana Bergstrom and colleagues from the Australian Antarctic Division. They showed the full effects of the cat eradication programme on the rabbit population and the terrible consequences to the vegetation of the island. Their report highlighted the need for integrated eradication programmes that examine the whole ecosystem and predict and plan for unintended consequences of the removal of invasive species.
The story could have ended there, a costly mistake both in ecological and economic terms. It is where the story ended for me until I started researching this piece. It turns out that there is a surprisingly happy ending as earlier this month the Australian and Tasmanian governments announced that Macquarie was officially pest free following the success of their eradication programme. This success means that Macquarie now beats Campbell Island as the largest island cleared of pests, an achievement that is of global significance. It’s an incredible feat, one I feared would be impossible. Though it will still take time for Macquarie to fully recover from the effects of more than 200 years of alien inhabitants, it now has that time. Finally Macquarie is home only to the birds and seals; a sub-Antarctic paradise has been restored.
Author: Sarah Hearne, hearnes[at]tcd.ie, @SarahVHearne
Cats eh? You either love them or you hate them it seems. Well the latest research published in Nature by Loss et al. (2013) will give those who hate them plenty more reason to do so. While those who love their cats may just sit that little bit less comfortably next to their feline companions.
Let me start by making a few things clear. Cats are predators, they are an invasive species which have been introduced to islands all over the world, by man. In many places domestic cats have become feral, i.e. reverted to living in the wild, which has led to huge increases in their numbers in some places, which can have a devastating effect on indigenous wildlife populations. For a more detailed and somewhat depressing example of where this has occurred read about Stephens Island in New Zealand. Famously a lighthouse keeper’s cat had been blamed for the extinction of an entire species on this island though it seems that reports may have been somewhat exaggerated in this case.
The report in Nature is more scientifically robust than urban legends about a lighthouse keeper’s cat though. Figure 1 below shows just how devastating domestic cats can be on local wildlife populations. The graphs show the estimates of predation by domestic cats on (a) birds and (b) small mammals.
Figure 1. Estimates of cat predation on US birds and mammals (from Loss et al. 2013)
The numbers are startling, an estimated 2.4 billion birds are killed by cats every year in the US and 12.3 billion mammals. Incredible numbers I’m sure you will agree, there is however a caveat; only 31% and 11% for birds and mammals respectively are caused by what the writers class as “owned cats”, cats which are regularly kept indoors and well fed. While the majority of the mortality is thought to be caused by free roaming “unowned” cats. Incidentally there has recently been some debate about wind farms and their impact on local bird populations but this excellent blog and another recent Nature piece put the numbers into perspective in terms of other anthropogenic causes of bird deaths.
As those responsible for the domestication and introduction of cats, we can’t lay all the blame at the feet of our feline friends. First of all we need to somehow effectively manage the populations of feral and “unowned” cats and while this has been attempted with the Trap-Neuter-Return movement, it has been viewed as a response based on regarding feral cats as part of the native fauna rather than the invasive aliens that they are , therefore largely unscientific and ineffective. Secondly pet owners can take several measures of their own, neuter or spay your cat while keeping your cat indoors at night can vastly reduce their impact on local wildlife.
