A coffee with Tim Brown
Kathy: Tell me a little about yourself and how you came into working on your Masters project.
Tim: Growing up, I was always inquisitive and had a love of science. Initially when I got to university, I was studying chemistry and mathematics and took an ecology subject just out of interest to see what it was like and really loved it. I found the ecological way of explaining things interesting. While I was doing this subject, I came across ecological trap theory which I found really fascinating.
Kathy: What are ecological traps?
Tim: Animals use certain cues or different aspects of the environment to determine whether a certain habitat is going to be good for them or not. We live in a dynamic world and habitats change over time. But usually this is quite slow process, so animals have enough time to adapt to any changes. The problem with urbanisation and other human impacts is that they’re changing the environment really quickly, and this can result in animals not knowing which habitat is best for them. Sometimes they’ll prefer a habitat that’s actually bad for them and this is what an ecological trap is.
Kathy: So what does your project focus on?
Tim: The project that I’ve been working on looks at how an invasive species can cause an ecological trap for a native species. Native species haven’t evolved with introduced species, so they might not be able to recognise them as a threat. If an introduced species does reduce their survival chances but the native species don’t avoid them, this can be an ecological trap.
My project looked at whether the introduced mosquito fish forms an ecological trap for the threatened native wetland dwarf galaxias, which is found around Melbourne. We looked at if the dwarf galaxias had lower survival when mosquito fish were around. We also looked at if dwarf galaxias could recognise them as a threat and avoid them, or if they will remain in areas where they are present, even though these areas are worse off for them.
Kathy: Why were mosquito fish introduced in the first place?
Tim: Back in the 1920s and 30s they were introduced worldwide as a form of mosquito control to try and tackle mosquito borne diseases such as malaria and dengue fever. They were introduced to eat up all the mosquito larvae, but there was little evidence that this was the case. Since they’ve been introduced, we’ve found that they like eating native frogs’ eggs and amphibian larvae, so they’ve had a lot of bad impacts on native wildlife. There hasn’t been a lot of work done on their impacts on native fish like the dwarf galaxias, but people think they have a really big impact on them. With my research, we were hoping to find out whether this was the case.
Kathy: Why are the native dwarf galaxias species so important? What’s their value in the ecosystem?
Tim: We always want to preserve local and native biodiversity. In some of the wetlands around Melbourne where they exist, they are the only native fish species present, so they are really important for biodiversity in these areas. If they completely disappear, these ecosystems would be dominated purely by invasive mosquito fish.
Kathy: What did you specifically research in your project?
Tim: There were two aspects to it. First, I looked at the different life stages of the dwarf galaxias and observed which ones were most impacted by mosquito fish. With the life stages that were impacted, we looked at if these stages recognised mosquito fish as a threat.
Kathy: What did you find?
Tim: We found that the eggs weren’t getting eaten at all, which is really good. But as soon as the eggs were hatching out into little larvae, the mosquito fish were just pouncing on them straight away. In terms of the later stages like the adult dwarf galaxias, we didn’t find evidence of predation. We did notice they were disrupting the breeding of adults so there was probably a significant effect there, although more research is needed to look into that.
Kathy: What was the second part of your research project?
Tim: We focused the second half of my research onto newly hatched larvae as this seemed to be the most vulnerable stage. We thought that maybe different densities of vegetation might impact the rates of larvae survival around the mosquito fish by providing refuge or helping them avoid predation. We found that low density vegetation had no effect and had the same predation rate as when there was no vegetation. But when we had dense vegetation, which was similar to the vegetation cover found in the wild, the rate of predation was a lot lower. This might be really important for the rate of survival of the larvae.
Kathy: Did the larvae see mosquito fish as a threat?
Tim: We did a series of choice experiments to see if they recognised mosquito fish as a threat and we compared their response to natural predators of dwarf galaxias larvae. We looked at whether they avoided the smell of mosquito fish or visual cues. The theory is that they’ve evolved with these natural predators so they will react and avoid these cues, whereas they haven’t had much time to evolve and avoid mosquito fish and see them as a threat.
In terms of being able to smell them, we found that they didn’t react to the smell of the mosquito fish at all, but reacted to the smell of natural predators. So, they don’t recognise mosquito fish as a threat in terms of smell. However, they did avoid the visual cues – when they could see mosquito fish, they swam away. But, we found that they also swam away from adult dwarf galaxias, so visually they weren’t specifically recognising mosquito fish as a threat either.
Kathy: How does your research contribute to dwarf galaxias conservation?
Tim: In terms of conservation, we found that it’s really important to have dense vegetation in areas where we know that mosquito fish are also going to be. In 80% of sites where dwarf galaxias are found, mosquito fish are also present. They spread really easily and are hard to get rid of. In many cases it’s not feasible to remove them, so it might be best to find options for them to coexist. If wetlands are restored or dwarf galaxias are reintroduced into new areas (which is something Melbourne Water is hoping to do), we need to make sure there is dense vegetation to provide refuge for larvae.
Kathy: I’ve heard about a project where quolls are being fed with cane toad sausages to try to deter them from eating cane toads as a way of teaching them cane toad avoidance. Do you think that maybe we could try and teach predator avoidance in dwarf galaxias?
Tim: I think it’s quite hard as mosquito fish are so widely distributed. In a lot of situations, they can’t really avoid them as they are everywhere so they can’t choose to exist somewhere else. This can make it difficult. Because it’s the newly hatched larvae which are most vulnerable, they need to know as soon as they hatch to avoid them, so there’s no real opportunity to teach them that. Maybe spawning adults could be taught to spawn in areas where mosquito fish aren’t around. It would be interesting to test if they preferentially spawn in areas where mosquito fish aren’t present.
Kathy: What are you plans after you finish your Masters this semester?
Tim: After I’ve finished, I’ll probably take a bit of a break, but potentially go on to do a PhD. I’ve also been doing a bit of science communication work and volunteering with a crew called Wild Melbourne, so that might also be something I would like to check out.
Kathy: Awesome, thank you so much for your time.