Non-invasive introduced species that benefit ecosystems

Nature Talk
21

Ecology invasive concern is so frequently conflated with industrial interests! The species might really just be a nuisance for growers, but because of lobbying or strateigc interests, recieves more attention than genuine invasives that don’t affect income generating crops.

WRT the posed question, I would say any continental species that are not present on close islands, that formed recently and didn’t get the opportunity to be populated by those continental species because of a water barrier. This is the case on many species poor islands, but it does assume that they are not important bird breeding sites, and since their ‘native’ habitat is so close, perhaps they should not be considered non-native anyway.

22

islands often have unique endemic species and if you introduce continental species, even ones present only a few dozen to hundred miles away, it could result in extinction of endemic species. Bringing a new species to an island is about the worst thing you can do, invasives wise

23

but only because native green anoles have a camouflage disadvantage in urban habitat over the non native brown (cuban) anoles

They benefit the environment by filling the niche. The habitat is degraded and can’t naturally support the niche they fill, so they benefit the environment by inputting energy in a niche that would otherwise not be present. I would argue that they actually do the same thing in natural as well as unnatural habitat, because naturally the different anole species occupy very specific niches (like twigs vs trunks etc.), and therefore fill formerly unoccupied niches and input more energy into the environment.

24

FL keys are an example, the first python found on key largo had two endemic Key Largo Woodrats in its stomach, which is like 1% of the entire population.

25

Good point, I don’t mean the exotic tropical hotspot islands of long-standing, but the recently isolated temperate ones off the coast of NW europe. I made the disclaimer because even some of these species-poor islands can be important bird havens precisely because they are species poor.

26

Fair point but…
Not to get too far side tracked from the main thread but…

Although you say the green “can’t support the niche they fill in degraded habitats” (paraphrased) which is partially incorrect, they can, and do still exist in urban environments, they are just more likely to be predated. Without the introduction of brown anoles, there would simply be less green anoles at first and then with time an increase in less green morphs. The increase in less green morphs in urban areas is still seen even with the introduction of cuban anoles.

One of the trends of invasive species is “specific traits that allow them to out-compete native species” So going on the original question of the thread, it was asking about non-invasive introduced species and cuban anoles are considered be an invasive introduced species.

https://www.cabidigitallibrary.org/doi/pdf/10.1079/cabicompendium.107830

“The successful occupation of different types of habitats by Norops sagrei (brown anole) is attributed partly to its use of thermo-regulatory behaviours such as basking in solar radiation to select acceptable microclimates at different latitudes and altitudes(Rogowitz,1996). It is reported that brown anole when present, reduce the density and diversity of spiders upon which they feed (Wardle, 2002). Greeneet al. (2002) state that, brown anole competes successfully with native green anole (see Anolis carolinensisinIUCN Red List of Threatened Species) and other introduced congeners. Campbell (2002) observes that without the brown anole,the native green anole occupies perches from ground to crown, but the presence of the brown anole causes the green anole to move higher, occupying trunks and crowns of trees. Brown anole demonstrate intra-guild predation (IGP), which is defined as killing and eating among potential competitors and have been reported to prey on the hatchlings of green anole… (Nicholson et al. 2000).”

“Anolis sagrei may have negative impacts on native herpetofauna. For example, it has been implicated in declines of the North American green anole (A. carolinensis) in southeastern USA (Campbell, 2000) by predation (Campbell and Gerber, 1996; Gerber and Echternacht, 2000), interspecific mating (Sater and Smith, 2018) and competition (Losos et al., 1993; Culbertson and Herrmann, 2019), with induced habitat shifts and decreases in population density (Campbell and Echternacht, 2003). Experimental introductions of A. sagrei showed that it increased dramatically in density at the expense of native A. carolinensis (Campbell and Echternacht, 2003). Furthermore, asymmetrical intraguild predation exists between introduced A. sagrei and native A. carolinensis from Florida and A. conspersus from Grand Cayman (Gerber and Echternacht, 2000). However, scientific studies have shown, or suggested, declines of green anoles where brown anoles are present; though none concluded that brown anoles caused the local extinction of green anoles (Campbell, 2000; Cassani et al., 2015). Furthermore, the recent establishment of A. sagrei in Bermuda has been identified as a potential threat to the survival of the critically endangered Bermuda skink, Plestiodon longirostris (Stroud et al. 2017), but no further evidence is available. It is observed that the Miami blue butterfly (Cyclargus thomasi bethunebakeri), listed as endangered under the US ESA 1973 (as amended), was preyed upon by an adult brown anole lizard (USFWS, 2012)”

I would still say it is not an overall benefit and at least neutral in certain environments. Like some other examples in this thread you are only considering them to benefit the ecosystem because of initial human disturbance. It is complicated since the decline of green anoles is partly due to urbanization but also because a new species is better adapted for the new urban environment. As studies show the out-competing of brown over green extends beyond urban environments.
But as Non-native species dominate herpetofaunal community patterns in both native and non-native habitat patches in urban Miami-Dade County shows one of their conclusions “our study did not find evidence of a direct negative impact of non-native abundance on native abundance. Instead, we found a positive correlation between native and non-native herpeto-fauna abundance” but that was a more general study on herps not focused on just anoles.

27

Whenever I hear someone say “Outside cats destroy endangered birds,” I want to ask them, “Which endangered birds live in your neighborhood?”

I don’t normally see cats in undisturbed habitats. When I think of “barn cats,” kept to control rodent populations in agricultural zones, I do wonder what native predators of invasive rodents would live in that habitat.

28

I will say i think working barn cats are better than anticoagulant pesticide, for sure. There are definitely places where cats are reducing songbird populations, but i think ecologically the impact varies

29

Even if feral cats don’t destroy endangered birds they definitely do have an impact on wild bird populations, whether the species are endangered matters less imo.

Some interesting reading:

https://www.hahf.org/wp-content/uploads/media-4/Jessup-article-on-Wildlife-impact-javma_225_9_1377.pdf

https://sci-hub.st/https://doi.org/10.1016/j.biocon.2017.08.006

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1027&context=icwdmother

30

Usually the whole cat argument is about general bird populations, not specific species, as @dgwdoesthings mentioned.

Having a predator whose population size is completely independent of that of its prey is, at least coming from my rather limited understanding of population ecology, quite bad. (Especially in places where small feline predators didn’t really exist prior to the introduction of house cats).

For comparison: In Germany there are 6000-8000 wild cats (Felis silvestris), however the number of house cats is 15.2 million.

31
  1. In europe (and most of the old world), cats are not a problem, since birds know how to avoid them, as there are native cat species in most of the area. In europe the domesticated cat poses the biggest threat to native forest cats, not birds (genetic erosion, although for now it looks hybridisation is fairly limited)

In Americas and australia, where that niche of small-feline prdator is largelly unfilled (or is filled by larger species or with species with slightly different ecology), it is a much bigger issue, as many birds do not have adaptive mechanisms to deal with cat’s presence. It does not help that we have probably bred bloodlust into domestic cats.
It is known cats contributed or were solely resposible for several bird extictions.

  1. that you do not see the cats in undisturbed habitat, is no indication they are not present; feral (and wild) cats are very good at avoiding humans, and are mostly active when we are not.

  2. Depends where you are, but most agricultural pest rodents are also invasive, so no natural predators; barn cats are fairly effective at reducing their populations and are more environmentally friendly that pesticides. So spayed and neutered barn cats can be a good solution to this problem.

32

To answer the original question, I think the answer will depend on what your goals are. I live in Haiti and am involved in a small land restoration project. In my context the land is so damaged and the remaining small stands of trees are so pathetic that I seriously doubt the natural/native habitat will ever be truly recoverable. Consequently we are using and have brought in a handful of non-native species with the hope of simply creating a forest, any forest.

We’ve found Leucaena diversifolia and Calliandra houstoniana growing in the nearby “forests.” They’re not native and are technically invasive but they actually grow and they fix nitrogen. They might out compete the few remaining native trees but those will be chopped down for fire wood within a generation anyways. Everything is so badly destroyed here that it’s hard to believe that adding non-native trees could possibly be a bad thing. The native birds are gone. The insect biodiverity is gone too. All that remains are the starving people, their starving livestock, and the ever present snails and crickets and katydids that eat everything that attempts to grow back. I’m exaggerating a little but destruction here is pretty profound and depressing. I’ve even wondered is something as invasive as kudzu might be a blessing here. If it could actually out compete the hungry livestock, which I doubt, then the land will have more nitrogen and the people will all around have more to eat. In this context it’s hard to remain a purist. If a few more species go extinct but I don’t have to see a neighbour’s child a day away from starving death again I guess I see that as a sad but OK trade.

Obviously in an ideal world, everyone would rally together and feed these people, teach them how to restore their land, teach them the value of the native biodiversity, etc. Maybe restoration could start the Dominican border and spread west. Obviously this would be far superior and be more sustainable in the long term. The reality is though that the prospect of this happening on a large enough scale to actually bring about real change is zero. The world doesn’t really even care that the gangs are raping a pillaging this country for all it worth. The people of Haiti clearly aren’t currently able to solve this problem alone. What do think the chances are that anyone cares enough, or has the means, to protect the remaining few birds and endemic plant species?

Sorry for the depressing essay. This issue tears me up a little. I love biodiversity. I know the native species are valuable. I know they all depend on each other to live. I hate to see the destruction of these natural gifts. I just also hate seeing the dying children. I not exaggerating when I say that around 15-20% of children die here before age 5. In the 4 years that I’ve lived here I have seen dozens of severely malnourished children. I’ve had people die in my yard. The land, as it currently stands and and in the way it’s used, just can’t support the population. Something needs to change or this suffering is just going to continue.

33

Agreed we don’t really want to be derailing the thread, but just real quick lol… It seems like you’re saying that coloration is the disadvantage which green anoles have, but the green coloration is not disadvantage because green anoles don’t actually exist in ‘morphs’ they can change color, so if that were a disadvantage anoles would simply be brown. It is more the lack of habitat, as greens are more arboreal than browns which displaces them (and possibly also pesticides tho that would probably impact both). And yes, greens are very much still present in suburban areas but are restricted to areas with more vegetation, whereas you can find browns on sidewalks along busy intersections in downtown Miami where greens are actually completely absent. I strongly disagree that browns have displaced greens to the extent that is popularly believed, because in natural areas, like Corkscrew swamp in my area, you find that there is a huge population of browns, because they are more prolific, but you still find that greens have a robust and stable population. I have heard it said that greens are simply becoming more arboreal to avoid competition, even to the extent of having enlarged toe pads. So I guess it depends on what your definition of invasive is, because I guess you could argue that that displacement in itself is evidence that the species can’t coexist.

Regardless of brown anoles, my original statement still stands because I din’t actually say brown anoles, just anoles. Knight anoles fill a niche (‘arboreal giant’ or 'canopy giant or something like that) not filled by native species. Same with bark anoles, in a different niche. Simply occupying an unoccupied niche is beneficial to the environment because it adds energy to the ecosystem without putting unnecessary strain on natives.

34

It seems like you’re saying that coloration is the disadvantage which green anoles have, but the green coloration is not disadvantage because green anoles don’t actually exist in ‘morphs’ they can change color, so if that were a disadvantage anoles would simply be brown.

While yes green anoles can change color it’s not camouflage to match a background(like chameleons) it’s usually behavioral or seasonal based on breeding. They still have differences in base color on top of changing colors. As you say, it is a disadvantage in certain habitats.

Simply occupying an unoccupied niche is beneficial to the environment because it adds energy to the ecosystem without putting unnecessary strain on natives.

I will mostly agree, the fundamental niche of both species overlap but in most cases the realized niches do not.

35

I have never seen any research to support that, although I certainly wish it were true.

36

They also destroy breeding populations of common birds. Cats live at a density that cannot be duplicated by wild carnivores because of supplemental feeding by humans. The decline in common birds is an underappreciated issue because they are common and shifting baselines allow us to ignore how much more common they actually used to be. Outdoor cats are a plague and should be culled at every opportunity.

37
  1. In europe (and most of the old world), cats are not a problem, since birds know how to avoid them, as there are native cat species in most of the area. In europe the domesticated cat poses the biggest threat to native forest cats, not birds (genetic erosion, although for now it looks hybridisation is fairly limited)

In Americas and australia, where that niche of small-feline prdator is largelly unfilled (or is filled by larger species or with species with slightly different ecology), it is a much bigger issue, as many birds do not have adaptive mechanisms to deal with cat’s presence. It does not help that we have probably bred bloodlust into domestic cats.
It is known cats contributed or were solely resposible for several bird extictions.

@ljazz unless you have science supporting that stamens, I unfortunately don’t think that’s the case, with the obvious exceptions of islands. Bobcats are generalists that are only marginally larger than house cats and are widespread throughout North America. In central and South America you have far more small cat species than in Europe. I think the problem is likely more cultural with how feral cats are thought of, which allows them to persist abundantly and predate wildlife.

38

This is the tricky part of this question. How do you define what is ‘beneficial’ to an ecosystem without considering a human perspective? Just about any change you make to an ecosystem will have positive and negative impacts on the existing species.

For example, someone mentioned clover as a helpful introduced species because it adds nitrogen to the soil. However, it is actually invasive in many locations. And while adding nitrogen to the soil is beneficial to some plants, it also changes competitive relationships to the detriment of others. Many endangered habitats are defined by their low nutrient status.

As far as examples of beneficial introduced species, there are a slowly growing number of biological control agents that have been established outside their native ranges to control other invasive species. While it’s true that there have been some ‘backfiring’ in the past, the modern approach to biological control includes extensive target vs non-target feeding trials that largely eliminates this risk. A recent success is the control of the weed hounds tongue by the weevil Mogulones crucifer https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/ecs2.1280

39

I too disagree with @ljazz that cats are not a danger to small wildlife in Europe because they live at far too high a density to not be. I also disagree with you that the bobcat is an equivalent comparison. Bobcats are not nearly as focused on smaller prey especially birds. Their main prey is larger rodents, squirrels, and lagomorphs. You are right that the biggest problem is human attachment to cats which causes them to feed them outdoors which allows for them to way overpopulate compared to the available prey in a given area.

40

I don’t think this type of language is particularly productive, since it makes cat lovers get all up in arms. Ultimately, it’s the cat lovers that prevent cat removal where they’re harmful. You need to at least give those people a chance to adopt the feral cats, since they purport to care about them so much, before killing them.