Thursday, April 25, 2013

Keeping Up With The Conversation

I'm a regular reader of the Native Plant & Wildlife Gardens Blog and was delighted that Doug Tallamy did a guest post there recently. But he's responding to this article over at Transatlantic Gardener which was a neat read in it's own right, especially down in the comments.

So second paragraph:
She grew well over 400 different plant species - garden plants and weeds, natives and non-natives - in her garden (below, click to enlarge) which measures just 741square meters (8000 square feet). And she counted 23 species of butterflies, 375 species of moths, 94 species of hoverflies, 121 species of bees and wasps, 305 species of bugs, sawflies, lacewings and related creatures; 21 species of beetles, 122 species of other insects including two ants – all in her suburban garden.
Umm... if you're only finding 2 species of ants then you either didn't care about ants in your study or you're doing something wrong. Though I don't think it's worth me getting into here, I've even spoken with Doug Tallamy himself as to why ants are the most abundant insects one earth and yet he only mentions them in "Bringing Nature Home" once and it's more in referent to aphids. Ants are more dependent on soil type and resources available than any special relationship with plants native or non, fair enough. But to only find two species is kind of alarming in my mind.

So in the next few paragraphs Dr. Owen looked into what all the moths were eating and (either her or the blogger) found they favored nonnative plants, but I wonder exactly what her definition of native was. First and foremost, let me explain that Lepidoptera (and insects in general) don't follow the boundaries or dotted lines drawn on maps. The Black Swallowtail is native to the US and Canada, and it's native host plant is Golden Alexander, Zizia aurea. However it's only restricted to eating plants in the Carrot Family, so when Parsley, Fennel, Queen Anna's Lace, Hemlock and the others were imported, suddenly the Black Swallowtail found the abundance of all these nonnative host plant beneficial and has since spread its range some.

In reading through the comments on that post it's clear that almost none of them understand the argument at all. Bamboo is beneficial becuase lady bugs over winter in it??? But then a few people come in and say the same thought that I had. Is Dr. Owen (or the blogger) also counting the use of nectar plants and host plants? Because you can't really do that and compare it to the work of Doug Tallamy. Host plants, native or non, are the plants the butterflies and moths look for to lay their eggs on and thus generate more butterflies and moths. Whereas nectar plants are useless kind of useless in this study; you can get the same results by spilling a soda or enlarging the holes in your hummingbird feeder. 

Nectar is also a temporary resource, where as the foliage of the plant tends to be around for several more month of the year regardless of what plant we're talking about.

Going back to the Native Plant & Wildlife Gardens Blog Doug Tallamy even points this out (in so many words).
She found that 46 species of moths fed on 40 native plants in the garden, while 75 alien plants provided food for 38 species of moth.  That is, if she had planted a garden of only the 40 native plants, she would have supported 46 species of moths. If she had planted only aliens, she would have supported 38 species of moths.
So it takes almost twice the number of alien plants to feed less than half the same number of moths. I swear sometimes it feels like Doug Tallamy is the only one able to do math.
Dr Owens found that non-native species were better as food plants for moth larvae than native species. Moth larvae used 27% of the native species in the garden as food plants, and 35% of the alien plants. And 46 species of moth fed on 40 native plants in the garden, while 75 alien plants provided food for 38 species of moth.
I read this paragraph and didn't pick up that the numbers didn't make any sense. The second sentance doesn't support the last sentance. And it's a coin toss what he means by Food Plants, and Fed On.

I live in North America and since I've been gardening with native plants, I'm seeing a lot more Lepidoptera species diversity, and more caterpillars overall.




1 comment:

  1. Its probably likely the variability in adaptability of the insects that might vary with some with preference and some with non-preference. It seems Swallowtails are on the rise do to their adaptability to alien hosts. Being able to bridge this gap is crucial to dealing with invasive plants as this allows the struggle to start to swing back into balance.


    Obviously a lot more study needs to be done to really know this on any specific level without assuming things.

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