In the past, praying mantises of all sorts were looked upon as beneficial insects that consume insect pests. A few things have changed in this regard. For one, insects in general are becoming fewer. My observations haven't been systematic, but I've noticed a steep decline in pollinators in the past few years, and a coinciding increase in insect predators, particularly Chinese praying mantises. And it's a stretch to believe a predatory insect is going to only consume insects that we consider harmful. Last fall, I found one chowing down on monarch butterflies.
Past posts on praying mantises.
Yes! They are huge and they are always prowling around the milkweed (monarchs) and eyeing the orange sulphur caterpillars...
ReplyDeleteWorth knowing that "invasive" doesn't require a formal listing. The federal definition under Executive Order 13112 is harm-based, and Chinese mantids meet it. The bigger issue is the lag phase. Most of the worst invasions we know, buckthorn, garlic mustard, multiflora rose, looked stable or harmless for 50 to 100 years before populations hit a threshold and impacts became undeniable. Chinese mantids have been here since the 1890s and are actively sold and redistributed by the millions every year through the garden trade, which artificially resets that lag phase constantly. We're not watching a naturalized species find equilibrium. We're watching a commercially amplified one.
ReplyDeleteThanks for your comment. Looks like you are or were based in SE Wisconsin, where I grew up. I'm trying to get the word out to WI and MI to catch invasions of lesser celandine and stiltgrass early, which are apocalyptic in NJ but starting to show up in the midwest. Heading the other direction is buckthorn, the first of which I found in Princeton last year. Interesting about the lag phase. Is it the plant that changes, or the climate, to make it start behaving invasively?
DeleteI'm the webmaster for the Southeastern Wisconsin Invasive Species Consortium and follow many invasive species trends. I know we are really looking for the stitgrass here. I deal with buckthorn and honeysuckle on my property. Awful stuff, but manageable once you get it down.
DeleteI found the first Chinese mantis last fall in my yard. Laying an egg case, so there must be others around. I wish they glowed under UV like scorpions. I'd go out at night and vanquish them all.
On the lag phase question: it's not always the plant that changes, but sometimes it is. The primary driver in most invasions is demographic - small populations grow slowly just from math, and once a density threshold is crossed, growth goes exponential. The "explosion" we notice is usually late in the curve, not the start of it.
But there's real science showing biological change during invasion too. Rapid evolution is documented in invasive populations - the EICA hypothesis (evolution of increased competitive ability) proposes that enemy release frees up resources that get reallocated to growth and reproduction over generations, and there's empirical support for it in multiple species. Separate introduction events can also produce admixture between lineages, creating hybrid vigor that wasn't present in the founding population. For plants, epigenetic shifts are on the table as well. Garlic mustard in North America appears to be evolving toward greater aggressiveness over time, not less - which cuts against the common assumption that invasives eventually settle down.
Climate is real too, but usually more about opening new habitat than flipping a switch in the organism itself.
So the honest answer is: lag phases are mostly a population dynamics story, but the organism can genuinely change during that window in ways that matter. It's probably both, in varying proportions depending on the species.
Now you have me thinking about whether there's any synergy going on between winged euonymus, privet, Linden viburnum, and multiflora rose, since so much of our preserved forested land has that admixture, with Pourthiaea villosa and barberry thrown in. You probably haven't witnessed Pourthiaea (Photinia) yet, as it spread from local nurseries here. I'd say it closely resembles common buckthorn in behavior. Did any of the common invasive plant species coevolve somewhere else, or is it just one crazy cocktail?
DeleteIf it doesn't have one already, the term "enemy release" needs its opposite, something like "enemy encumbrance" or "enemy augmentation," since that's what happened to native species in NJ as the deer population grew, thinning out native species to increase opportunity for the invasives. And again that's happening as Emerald ash borer and diseases like beech leaf disease open the canopy, directing more resources to the nonnative understory. Maybe there's a term already out there for the sort of piling on of enemies that native plants are experiencing.
We are lucky in Princeton to have deer culling since 2000 to keep numbers down, allowing spicebush in particular to flourish once again. The other good news is that we, or at least some managers in some locations, have been able to intervene early in the introduction of species like Japanese Angelica tree, jet bead, and even lesser celandine. It takes strategic timing and persistence--two traits that aren't always easy to cultivate in people's thinking, given we're such a distractible species. Given the potential for success via early intervention, it makes one realize the enormity of deferred maintenance that has accumulated with the more entrenched invasive species out there.
If we could just make it illegal to sell any non-native species with invasive potential, we could save billions/trillions of dollars in the future. Why isn't Callary pear listed everywhere? That species is going to give buckthorn a run for its money. It’s mind-blowing that we can't do anything without it being some kind of money-making scheme.
ReplyDeleteIt took years of hard work to get NJ's Invasive Species Council re-constituted after it was terminated by Governor Christie, and even then, regulation of the small list of invasive species agreed upon will not begin for another four years. So, yes, economy over nature for sure.
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