I did my master’s thesis on priority effects, which I believe is the term you are using. Priority effects mean that the first species to arrive in a newly formed habitat can adversely affect the establishment of later arriving species.
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I see what you mean. My professor friend told me that Gambusia are naturalized here by now, and that if it was his pond he would just leave them be. He also said that frogs and great kiskadees would feed on them occasionally, as well as odonate nymph (but again I haven’t seen any inside the pond, tho maybe im not looking well enough) so now im not sure what I should do. Would maybe taking out some of the gambusia periodically and adding pearlfish be a good idea to counter-balance their population?
And in regard to priority effects, what I don’t get is how if the gambusia arrived to the pond months after it was created and filled with different animals how they manage to have such a population boom. Is it maybe because they are in an ecological niche that no other species was in? They seem to be feeding mostly on plant material, although tadpoles feed on it too. Or is it just that there were enough resources and lack of predators that they could just expand without much concern?
Again, thanks so much for your advice. Im sorry if it seems like im wasting your time with all this questions, your answers really help me out tho! Ecosystems and their management are way more complex than I ever expected them to be, so it has proven quite a challenge for me to strike the balance between letting nature do her thing and making sure its all going as planned. I’d love to be able to manage a bigger piece of land in the future and this small pond is giving me a taste of what that would be like, so I hope all that im learning thanks to you guys will be useful then. Again, thanks so much for taking the time to explain all of this.
mosquitofish are native in my area. there’s a local park / nature center that i go to once in a while that has lots of different ponds with different conditions, and all of the ponds have mosquitofish in them. from what i can tell, bigger predator fish – if they exist in your area (and your pond is big enough for them) – are going to be the best biological control, but they still won’t be able to eradicate. birds, frogs, dragonflies, raccoons, etc. might eat an occasional fish, but they barely make a dent in mosquitofish populations. i’ve seen some of those ponds dry up, and then snakes come in and eat all the fish, but then when the ponds fill up again, the fish find a way back. the staff at the park tell me they’re not moving the mosquitofish in. it’s possible it’s random people doing it, but i think birds are more likely vectors, or else the fish are swimming in themselves during floods maybe.
regarding population booming, i know folks who raise mosquitofish, and they can easily fill giant tanks with mosquitofish in a few months, starting with just a few fish, since each female can produce tons of babies over and over. i’ve never raised them myself, but the numbers i see on Wikipedia are roughly 2-4 week pregnancy, with 60 babies per batch, and then 3-4 weeks to maturity, under ideal conditions.
i would guess that if you don’t know how the fish got in your pond, but there are likely sources nearby, then eradicating them from your pond is ultimately going to be wasted effort, if you don’t / can’t address other potential source bodies of water.
that said, if you’re going to remove mosquitofish from your pond, i think it might be interesting to put them in a small white plastic tub nearby to see what might come to eat them. (you can poke some very small holes in the side of the tub to make sure that the tub won’t overflow and let the fish out when it rains, and you can put some support around the tub to make sure an animal won’t accidentally tip it over.)
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Before you let it go dry (if you do), I wonder if it would be interesting to look at samples of the water and sludge at the bottom under magnification to see what micro-organisms may be living in the pond? Then, when the pond is re-established, take a look at the new samples for comparison?
Do you have a microscope or possibly could use one at a local school?
I used to have a little ornamental pond with plants and goldfish and it was truly amazing to look at the multitude of smaller life forms under magnification (I used a microscope at the local nature center).
There were so many plants and critters in my pond* (I used a biological filter, no chemicals). I did not even need to feed the gold fish - eventually, they preferred the natural diet they found in the pond to commercial pond food.
*by contrast, when I took samples from the nearby reservoir to view under the nature center’s scope, all I usually saw was dead plant matter. I was surprised, as there are lots of birds and fish and turtles that live in the reservoir, but very little too see in the microscope compared to my patio pond.
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@teellbee I will be sure to check if I can find someone with a microscope that I can borrow. I doubt I will get access to any in a school since they are all closed due to covid. Also, it seems so strange that the water reservoir didn’t have any microscopic organism, aren’t those usually needed in order to have bigger animals? Cause the way I see it, microscopic critters are food for small fish, which are in turn food for bigger fish and so on. Perhaps people have been feeding the fish and turtles in the reservoir instead and that’s why they can thrive regardless?
For now I’ve decided to make the pond a bit bigger, since we’re getting a bit of less hot weather so I can dig without risk of overheating, lol. Once the extension is complete I will connect it to the main pond and not fill it with anymore water. That way it will dry faster, I think. If the rains continue filling the pond however I may just stick to manually removing gambusia and try to add pearlfish so they have some competition.
And @odole: thanks again for all the kind advice. I see you seem to like odonates a lot, would you be okay with me occasionally tagging you in any odonate observation I make in the pond? There’s quite the variety! There’s this specially big red dragonfly that visits it all the time, but I haven’t managed to take her picture so far.
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FWIW, the county rules out feeding wildlife in this park and it is very rarely done. And, you always see the geese, ducks, coots, and piebald grebes diving for food. The reservoir had fish, abundant water birds, turtles, and plants. It is also used by humans for summertime kayaking, paddle boarding, and small boat sailing. The water looked like murky tea, so it seemed promising. I sampled it’s water several different times in different places, including climbing down the bank into the tule and cattails to get a sample around their roots. Nada 
The lack of microorganisms in that little reservoir’s water remains quite mysterious to me. I did not scoop up sediment from the bottom, and perhaps I should have done that. I wondered if the water had been treated as it is nominally part of the district water supply. I can’t say I think it is likely, given that the water feeds percolation ponds further downstream.
By contrast, my tiny backyard pond water was satisfyingly full of micro-organisms. I used the same microscope to look at all the samples.
Just as an aside, patio pond had a biological filter that required cleaning every few months. I would pull out the filter media and put in a large pail and hose the sludge off. The stuff I hosed off was sprinkled on plants around the patio… it was the very ~best~ fertilizer I have ever used and all organic, too.
I miss having that awesome fertilizer producing itself in my own patio.
If you are going to drain the water anyway, I wonder if you could try a bucket or two of its bottom water on your plants?
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Have you considered creating an ecosphere with just some reservoir water and sediment? You could put it inside a sealed jar and see what happens! I’ve never made one, but Life in Jars has a youtube channel dedicated exclusively to that kind of stuff, so that would be a good place to start.
Would the bottom water be any different from the surface water nutrient-wise? I usually splash a bit of pond water on any surrounding plants that seem to be drying up, but it doesn’t help much I think.
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I think I phrased my question wrong haha, I meant to say it as in if you would like to see the dragonflies and be tagged whenever I find a new one. As in if you would be interested in seeing the odonates that go to the pond since you said the project was interesting, so I thought you might like to be tagged in future observations. It’s perfectly fine if you prefer not to, tho!
But your idea seems pretty cool. I’ll send roget a message and let him know about the pond and what he thinks I could do to encourage odonates and their survival there. Thanks!
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Haha it does indeed seem like a lot of information for me to take on. I think for now I’ll work to preserve the pond and maybe expand the range of different “micro-habitats” that form around it. Sadly a few days ago the neighbors “cleaned up” a property that was adjacent to ours in which there was one of the last remaining shrublands around, only leaving a small triangle in the corner where the tractor could not get to. Im not sure if that will affect the odonates, but it has certainly affected the cavy and likely any other animal that lived there.
I swear the more I think about it the more I want to purchase a large piece of land in the Patagonia and make an ecological reserve there, lol. But that would likely requiere tons of experts’ advice as well, wouldn’t it?
For now tho, this are the only two observation of odonates I have in the area so far. Here’s hoping I get to document some more soon!
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Well, the Patagonia is big and still does not have so many people. I think a small reserve in Buenos Aires is also very important to help the wildlife near the city, although I agree it may feel harder to ‘protect it’ from the outside.
In permaculture they say: the problem is the solution. You now have too many mosquito fish, but maybe you need to wait for a predator to find them.
I have hopes that some water bird will start soon fishing on your pond, maybe comadrejas or other fish eating mammals.
Maybe you can leave a bunch of them in a clear bucket so passing birds will notice them and start fishing on the murky pond waters. A bit like advertisement.
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