Climate anomalies and competition reduce establishment success during island colonization (2022) Nicholson et al., Ecology and Evolution, https://doi.org/10.1002/ece3.9402
The colonisation of islands by species on the move has given rise to some of the most fascinating ecosystems around the world. Think the marsupials of Australia, Papua New Guinea’s Birds of paradise, or the multitudes of weird and wonderful creatures that pop up in tiny unexpected landmasses around the globe. On the flipside, invasive species arriving on islands can hit like veritable hurricanes, with similar (though admittedly slightly slower-moving) effects. Yet for these phenomena to take place, a species first has to make it to an island from the mainland. This isn’t always super easy, seeing as islands may be tiny and hard to find, or way out in the middle of nowhere.
But even if they do arrive, whether or not a species is able to persist depends a lot on circumstance. If a large storm or drought hits (increasingly likely with climate change upping the frequency of extreme weather events) just after a species arrives on an island, it might wipe them out before they’ve even gotten started. A competitor already having set up shop there could decrease a species’ survival chances too. Today’s authors were lucky enough to have introduced a new species to a series of islands with and without competitors, all of which were hit by a drought just after one of the introductions. Let’s see how the populations fared.
With increasingly clear effects of global climate change, everyone’s thinking about how we will handle extreme temperatures and weather events as they become more common. Less obvious is the fact that the changing climate is also rearranging global food webs, with many species readjusting in the fact of a new range of temperatures. This might not sound fantastic (and let’s face it, it’s not), but this changing climate may be able to teach us something about how species adapt to higher or lower temperatures.
Temperature plays a key role in determining whether an invasive species can take up residence in a new region. We know that low temperatures can be particularly limiting to newly-invasive species, especially insects and spiders. Yet few studies look at how lower temperature in a new environment can affect the survival, development, and behavior of new invaders.
We tested whether invasive widow spiders from a warm climate (Australia) adapted over generations to the lower temperatures of their invaded habitat in Japan. The move to Japan should require adapting to lower temperatures, but it might not, for a few reasons. Spiders from both locations may be equally good at coping with cooler or warmer temperatures, or, since urban areas are typically warmer than natural habitats, organisms that move between urban habitats might avoid facing the low temperature constraints.
Did You Know: Cities as Heat Islands
It’s hot in cities! One reason for this is the urban heat island effect, where urban areas are several degrees hotter than surrounding natural areas because of all of the heat-absorbing surfaces like roads and buildings. More than half of the human population lives in cities, and as they heat up, it is especially important to understand how some species adapt and even do better in urban environments. Urbanization and climate change can also increase the spread of invasive species. For example, some urban-adapted invasive species thrive in urban habitats that would otherwise be too cold for them to survive and reproduce in. Understanding how urbanization, climate change, and invasions interact can help us predict changes in biodiversity and species distributions in the future.
What We Did
The Australian redback spider, Latrodectus hasselti, is an invasive species of widow spider, native to Australia. Redback spiders are well-known in Australia for their bite and neurotoxic venom. Redbacks have been transported (likely accidentally along with used cars or produce) to Japan, New Zealand, the Philippines, Papua New Guinea, and India. We compared traits across native and invasive-habitat temperatures in a native population of spiders. The native spiders were collected from Sydney, Australia and the invasive population from Osaka, Japan, where redbacks became established in 1995.
We reared the spiders in the lab for three generations. We first checked for population differences in how spiders responded to extreme temperatures, measuring the lowest and highest temperatures at which spiders were able to maintain normal activity.
Next, we investigated how spiders respond to more moderate temperature differences, such as those in autumn, right before overwintering. When female spiders from each population produced egg sacs, we put the egg sacs for two weeks in either Japan-typical (15 degrees Celsius) or Australia-typical (25 degrees) autumn temperatures, then put all egg sacs at 25 degrees until spiderlings emerged. We predicted that the invasive spiders from Japan would be better adapted to low temperatures than the native Australian population, as they’re used to colder temperatures. We also measured hatching success, development time, and body size.
Once the spiderlings were juveniles, we measured behavioural traits that may be important for survival in nature: boldness – how quickly a spider resumed movement after a simulated predator threat (a puff of air), and exploration – building a web in a new environment.
What We Found
At extreme high temperatures, spiders from each population were similarly tolerant, with females able to move at temperatures of up to 55 degrees Celsius! Surprisingly, males from the invasive population from Japan were less tolerant of extreme low temperatures, suggesting that they may not overwinter successfully in colder regions. Egg sacs from the Japanese population hatched equally well at low and high temperatures, but egg sacs from the Australian population failed to hatch more often at low temperatures. Native spiders also took longer to emerge from the egg sacs than invasive spiders at low temperatures, which could expose egg sacs to more predation risk.
The Japanese population was bolder and more exploratory at low temperatures, but less bold and less exploratory at high temperatures, whereas the native population was similarly bold and exploratory at both temperatures.
Spiders from Japan, which live in cooler habitats, developed at both low and high temperatures, compared to a native population, which hatched less and developed more slowly when exposed to low temperatures. This study only tested one invasive and one native population, and it would be worthwhile to compare multiple invasive populations from both cooler and warmer habitats, as well as multiple native populations across Australia.
Although the invasive habitat in Japan is more extreme in temperature, spiders also live in more urbanized habitats compared to the native population. Urban habitats are hotter, and we would like to measure what conditions the animals are directly experiencing in the urban and natural habitats, to find out if spiders are able to colonize cooler climates because they thrive in urban heat islands habitats.
Some organisms may be better equipped to deal with changes we are facing with urbanization, habitat fragmentation, and climate change. In the case of Australian redback spiders, within twenty years, we found that an invasive population changed significantly in traits related to thermal performance, which may give them an advantage as temperatures change worldwide.
Behavioral traits are studied less frequently; finding increased variability in an invasive population may provide a clue to how the species can thrive in different environments. Understanding how organisms can establish and spread in environments different from their native ranges can help us predict which species will survive in our increasingly urbanized, changing world.
Dr. MonicaMowery is a Zuckerman STEM postdoctoral fellow in the labs of Yael Lubin and Michal Segoli at Ben-Gurion University of the Negev. She received a B.S. in biology and community health at Tufts University, working on butterfly visual signals and behaviour in Sara Lewis’ lab. Her PhD was conducted in the labs of Maydianne Andrade and Andrew Mason at the University of Toronto Scarborough, where she studied invasion success in widow spiders.You can read more about Monica’s work at her website.
As I write this, I can hear invasive myna birds chirping in the trees outside, and see yellow pollen from the invasive Acacia trees floating through the air. What makes these species able to thrive far away from their native habitat? Despite the knowledge of how harmful invasive species can be, humans continue to transport species to new environments, both intentionally and unintentionally. Yet even with the explosive growth of both invasive species and invasion ecologists, we still don’t know a lot about which traits make the most successful invaders that can thrive and spread to new places.
One way to investigate this is to compare invasive populations that have just arrived at a new place with populations that have been in an area for a long time. To better understand invasive species, we need to figure out how traits shift in invasive populations, as some individuals survive transport, establish, and spread to new habitats, expanding their range. When this happens, traits can change, or shift, as the species adapt to the new environment. Such traits, such as body size, number of offspring, and dispersal ability, may be particularly important during range expansion. This study is an investigation into how traits of invasive spiders shift on a broad geographic scale on two continents.
Invasive alien species as an environmental stressor and its effects on coping style in a native competitor, the Eurasian red squirrel(2022) Santicchia et al., Hormons and Behaviour, https://doi.org/10.1016/j.yhbeh.2022.105127
We know that human activities can cause enormous stress for local species, and the introduction of invasive species is one of the most harmful stressors on a global basis. We know that new, harmful species can cause local extinctions, but how does their introduction affect the locals on a behavioural level?
Grey squirrels were introduced to Europe last century and have been spreading since, displacing the native red squirrels and wiping them out in many areas. This week’s authors wanted to know exactly how red squirrels’ behaviour changed when the grey squirrels were introduced, by looking in detail at the behaviour of red squirrles in both invaded and non-invaded areas, and seeing if they could see evidence of these changes in the expression of hormones (more on this in Did You Know).
Last week, prominent Australian conservation scientist Professor Hugh Possingham caused quite a stir when he stated that “personally [he is] not convinced that climate change is a huge threat to many species”. This naturally sparked heated debates among ecologists the world over, with varying levels of vitriol. As Dr. Charlie Gardner put it, it “is an extraordinary thing to hear from a leading conservation scientist”.
I know I write a lot about whether or not we should jump to conclusions about non-native species, but the fact is that there are lots of situations in which invasive species need to GO. Giving them the boot, however, can be a right pain, and more often than not it’s impossible.
But an ounce of prevention is worth a pound of cure (I don’t know the imperial system well so I assume that makes sense), and figuring out where an invader is likely to turn up means you can take measures to stop it happening in the first place. This saves a lot of hassle (and money) down the road.
So how do we figure out where invasives are likely to show up? That’s what this paper, which made up the first chapter of my thesis, aimed to find out, by looking at where invasive freshwater fish species have been popping up in Norway over the last 100 years.
Distribution and establishment of the alien Australian redclaw crayfish, Cherax quadricarinatus, in the Zambezi Basin (2021) Madzivanzira, South et al., Aquatic Conservation, https://doi.org/10.1002/aqc.3703
While some of us may love certain seafood, and are willing to carry that seafood all over the globe, often the local species are none to happy about it. Such is the case with the Australian redclaw crayfish, a rare example of Australia finally delivering back to the world that which it has received so many of – an invasive species. The redclaw is actually one of nine crayfish that has been introduced to mainland Africa, and if their record (and the records of other crayfish species) is anything to go by, it could mean everything from the spread of parasites and complete ecosystem upheaval to severe damage to the local fishing industry.
It’s crucial to figure out exactly where invasives have spread to, and how quickly they’ve done it. It allows managers and conservation experts in other areas to prepare, and to keep an eye out. This week’s team tried to determine how quickly the crayfish are spreading from their introduction point in the Zembezi River Basin.
Every time fighter jets fly overhead here in Central Norway, either my wife or I nearly always make a dry remark about the Russians finally invading. It’s a slightly dark reference to former Norwegian occupations, but not something that’s likely to occur anytime soon.
Yet this summer, the papers were filled with constant sensational references to very real and ongoing Russian invasions. Luckily, they’re referring to the pink (or humpback) salmon, and not to any human army marching across the borders.
Horses are, without a doubt, a hugely significant part of human culture and history. Worldwide, they’ve played the role of food source, beast of burden, war steed, postal service, transport, and in modern times pet and sports star. Horses were and in many places still are are an omnipresent part of life. People have a lot of feelings about them.
Last week, the Commonwealth Scientific and Industrial Research Organisation (CSIRO) announced that they were going to import Moroccan dung beetles into Australia. The purpose being ostensibly to combat the fact that local Australian dung beetles have not evolved in step with marsupials instead of cattle, and are therefore pretty ineffective when it comes to breaking down the dung of sheep and cows. The introduction of the new beetles (specifically the Moroccan dung beetle, Gymnopleurus sturmi) is therefore intended to aid in the breakdown of cattle dung, returning nutrients to the soil, reducing the populations of the flies which follow cattle around and just generally cleaning the joint up. Sounds great. We’ve never had problems with species introduced to clean up our own mess before.
Ok but didn’t you introduce the cane toads to sort out your problems and now they’re everywhere?
YES YOU’RE DAMN RIGHT WE DID. For those less familiar with the poster child for biological controls gone wrong, the cane toad (Bufo marinus) was introduced to Australia mid last century to deal with the cane beetle, which was destroying sugar crops. Australian species, having no experience which a poisonous frog of this type, have been heavily affected ever since, and the toads spread like lightning.
So this is a bad idea?
Well not exactly. While many people are comparing this directly to Australia’s previous mistakes, there are some marked differences. Exotic dung beetles have actually already been in Australia for decades. We do have 500 native species of dung beetle (accounting for about 10% of discovered species worldwide), yet scientists from the CSIRO introduced new species in the mid 60s to combat the same problem they’re trying to combat now.
This initial project is not exactly a great look for the CSIRO. In a paper from 2018, Bernard Doube of Dung Beetle Solutions International and formerly of CSIRO pointed out that of the 53 species that scientists attempted to introduce, ten were never introduced and 20 never successfully established. Doube attributed some of this to poor understanding of dung beetle breeding biology, which is worrying, given that we should really know as much as possible about a species before we go dropping it into a new ecosystem. The remaining 23 have spread to varying degrees throughout what was thought would be their natural range in a country like Australia. So far, they don’t appear to have posed a problem for native species, and have done their job in some areas.
So why will these new ones make a difference?
According to the CSIRO, the dung beetles that they have introduced don’t seem to get much work done during the spring. That’s why they’re introducing the new species. They’re not hyperfunctional crazy shitrolling juiced up beetle monsters, they just work a different shift.
This seems… fine?
Yeah ok, BUT IT’S NOT. I don’t actually have a problem with the science, it SEEMS pretty solid and anything that sequesters carbon needs to be given a look-in these days. But the way the CSIRO seems to have ignored the obvious questions that come with this irritates me. Even without reading into this too much, it is perfectly natural for anyone with a passing knowledge of the cane toad debacle to question it. The CSIRO needs to, right off the bat, acknowledge that this might sound like a bad decision, and then be abundantly clear about why it’s not.
This whole thing brings to mind the recent decision to introduce genetically modified mosquitoes into Florida to deal with the Zika virus. The science appears sound, but goddamn the concept of human-made super mosquitoes suddenly being released sounds like the start of a horror film we don’t want right now. As an example of how this sort of communication SHOULD be handled, mosquito ecologist Kara Fikrig posted a fantastic explanation of why the mosquito introduction should work, linked below.
I genuinely believe that science communication is getting better all the time. And I think this project sounds promising. I just wish that in articles like this one, and the one linked below (both of which do a pretty good job of communicating the science behind the project), both the media and the scientists would do a better job of addressing people’s valid concerns about the use of exotic species as biological invaders.
Sam Perrin is a freshwater ecologist who completed his PhD at the Norwegian University of Science and Technology who didn’t make a single poo joke for this entire article and deserves your respect because of it. You can read more about his research and the rest of the Ecology for the Masses writers here, see more of his work at Ecology for the Masses here, or follow him on Twitter here.