Friday, January 14, 2011

Readdressing Same

I feel I must make further comment with regard to yesterday's post.

Here are a couple things we must keep in mind when we suddenly discover some benefits to invasive species.

1.  These data reflect the highly seasonal dietary needs of just three species of migratory birds.  What about the other migrants?  What about the birds that stay year round?  And what are these same three species eating during the spring migration when said fruits are not available?

2.  We have to look at the BIG picture.  For example, do these invasive plants have any other benefits, or are they highly selective?  Further example: are there any local insects that benefit from the presence of these plants, and on the flip side, are there insects that are negatively impacted by same?  What most of us fail to realize is that insects are vital links in most ecosystems, and many insects are dependent on plants (sometimes a single plant) as hosts at some point in their life cycle (food for adult, food for larva, shelter for adult, shelter for larva, shelter for egg, protection from predators via chemical compounds ingested....etc.).  Here is a terrific example of this whole point, about which I only learned this last year:  there is a particular butterfly (the mustard white, Pieris oleracea) whose larva has limited host plants, all in the native crucifera family (mustards).  These plants are becoming quite scarce, thanks to the incursions of that Top Ten Invasive Plant known as garlic mustard.  The larvae do not thrive on garlic mustard - it doesn't supply the nutrients they need for optimal growth. For a quick summary of this butterfly's status in Massachusetts, go here.

3.  What were these three species of birds eating a hundred years ago, two hundred years ago, thousands of years ago, before these non-native plants arrived on the scene?  There had to be suitable fruits around, otherwise the birds would've died off long ago from starvation.  So, if these non-natives were once more removed from the landscape (admittedly highly unlikely), would the birds find something else to eat, like the pokeweed fruits, which also featured high on the list?  Would they also turn to the dogwood fruits, and wild grapes?  Would they something else to snack upon that was high in sugar but low in lipids?

4.  What are the negative costs to the ecosystem created by these plants?  Do they out-weigh the benefits?

I'm sure that field biologists and researchers can probably come up with a much longer list, but I think this gets the point across.  Yes, it is very interesting that the birds actually do exhibit a benefit to having these invasive plants on hand, but that doesn't mean that we should let invasive honeysuckles, buckthorns, et al, run rampant and unchecked over the landscape to the expense of everything else.

Something to think about.

1 comment:

  1. Much to think about in this and the past post. Looking at the big picture is, indeed, necessary and that ability often seems to be something we humans are not so good at, especially since the big picture involves much interdisciplinary cooperation and interaction.

    Some species will always be able to adapt and even benefit from human-caused habitat changes, but my totally unsubstantiated and unscientific hunch is that in most cases the net benefit/loss will be negative, but exceptions are always possible. I'm glad there are better educated and trained professional than I to sort things out.