Tag Archives: insects

An Early Attempt to Evaluate Prairie Restoration Success by Looking at Insect Use.

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Back in February, I wrote a post that laid out some ideas about how to measure success when using prairie restoration (reconstruction) to stitch fragmented remnant prairies back together.  One of the main needs is to see whether species from the remnant are also using the restored prairie.  If I’m trying to make a small remnant prairie function as a larger prairie by adding restored prairie around it, the species in the remnant must be able to expand into and travel through the restored habitat.

I just got some data from a couple of volunteer amateur entomologists that apply to that kind of evaluation, so I thought I’d share what they found.  First, let me be clear that these are amateurs (“enthusiasts” may be a better term than “entomologists” – though they are much better at insect identification than I am!) and that these are not research data.  However, what they found was very interesting, and will make a good launching point for future work.

Four species of tiger beetles were among the insects found during the 2009 inventory work.

INTRODUCTION

In early 2009, I was approached by Chris Aubushon and Connie McCartney, who live in Grand Island, Nebraska – near our Platte River prairies.  Chris and Connie were initially just looking for new sites to hunt for insects, but as we talked, we developed a bigger idea.  They volunteered to come out once a month for during the 2009 growing season and collect as many insects as they could from 6 sites and to identify what they could.  The six sites were really three sites where I had a restored prairie next to a remnant prairie, and they collected insects from both the remnant and restored portions of those sites.

Chris Aubushon (left) and Connie McCartney (right) setting up plots for their insect inventory project in early spring 2009.

Again, this was not a research project, but Chris and Connie – and some helpers – did come out once a month for 5 months and collect a lot of insects.   They restricted their sampling to one 100 foot by 100 foot plot at each of the 6 sites, and used a combination of sweep netting and pitfall traps to catch the insects.

RESULTS

Chris and Connie were able to identify 136 species from those five months of collecting.  They also found (but didn’t identify to species) approximately 33 species of spiders.  When I got the list of species from Chris, I sent it to several friends of mine who are knowledgeable about insects to get their impressions.  The consensus among those entomologists was that the insects on the list were almost exclusively common species that are habitat generalists.  In other words, the list doesn’t include many rare species, or species tied to particularly “good” quality prairies.  Instead, Chris and Connie mostly caught insect species that can be found just about anywhere.   That doesn’t diminish their efforts, but it’s important to remember as you interpret the breakdown of results.

Of the 136 species caught, 28 were seen at only one site.  Interestingly, 8 of those 28 species were found only in remnant prairie, while 20 were found only in restored prairie.  (I don’t think it is necessarily important, but of the 20 species found only in restored habitat, half were beetles.)  Two species – a firefly and a burying beetle were found at two different sites that were not adjacent to each other.  In each case, they were found in one restored prairie plot and one remnant prairie plot.

The reference insect collection from Chris and Connie's work in 2009.

All of the remaining species (106 of them) were found in both halves of at least one remnant/restored prairie pair.  In other words, except for the two species mentioned above, every other species of insect found in more than one place was seen in both the restored and remnant portion of at least one prairie.  Remembering that these are all generalist species, I’m still surprised – and encouraged – by those results.  I had expected to see at least a few insect speces that were found in remnant prairies but that weren’t yet making the jump into the adjacent restored prairies.  In fact, I was kind of counting on seeing that so that I could design some follow-up data collection to figure out what the obstacles might be that were preventing them from using restored prairie.

CONCLUSIONS

So what have I learned?  First, the prairie restoration work we’ve been doing appears to provide adequate habitat for the most common and widespread insect species in our remnant prairies.  At least for those species, the restoration work we’re doing is successfully increasing the size and connectivity of fragmented remnant prairies.

Second, I’ve learned that I need to recruit a lot more entomologists to come collect insects from our prairies because every time I do, I learn something.  A little more than a decade ago, I worked with Kristine Nemec on her graduate school project to compare insects between remnant and restored prairies along the Platte River in Nebraska.  For her project, she inventoried insects in 3 restored and 3 remnant (degraded) prairies, but the restorations and remnants weren’t adjacent to each other.  Nevertheless, among grasshoppers, katydids, leafhoppers, planthoppers, and treehoppers, she found very few species that were found in remnant prairies but not restored prairies.  She also found very similar numbers of species between remnant and restored prairie for each of the insect groups she looked at.  You can see a brief summary of some of her thesis findings here. Nemec Results

Third, I’ve learned that the next steps in our efforts to evaluate insect use of our restored prairies will be harder.  We probably need to start by identifying species of insects in our remnant prairies that may not utilize nearby restored prairie – based on what we (meaning people besides me) know about their life history.  Then we need to do some targeted sampling to see whether they are or are not using those restored prairies.  It’d be even better if we could actually track individual insect movement to see if they cross the boundary between remnant and restored prairie.   (That should be easy, right?)  Broad sampling like we’ve done so far is useful, and a good first step, but now we need to hone in on a few target species and see what we can learn about them.  Species that rely on a particular plant species or that are tied to soil organic matter levels may be examples of those we need to study.

To sum up, there’s plenty of work to do.  To this point, we haven’t found any glaring problems with our restored prairies that are so severe that common insect species are restricted from using them.  That’s pretty nice to know, but it’s just the tip of the research iceberg.  Now we need to dive in and start working on the rest.

I’m extremely grateful to Chris Aubushon and Connie McCartney for all of their hard work collecting, sorting, and identifying insects for this project.  It was an amazing effort – and done for the simple love of exploration of the natural world.  Thank you.

I’m also grateful to James Trager, M.J. Hatfield, and Ted MacRae for helping me to interpret the results of the project.  Their comments and insight helped me tremendously as I worked to understand what conclusions I could and couldn’t pull from these data.

The Importance of Weedy Flowers for Butterflies

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In our Platte River Prairies, regal fritillaries and other butterflies appear to depend heavily on a few weedy wildflower species as nectar plants.

I was in graduate school when I first started learning to identify butterflies.  I participated in several July 4th butterfly counts around Nebraska, and got to know some people who could help me with the tougher-to-identify species.  I was a good birder at the time, and quickly found many parallels between bird and butterfly identification.  One of those was that skippers were just like sparrows – lots of small drab-colored species that were really difficult to tell apart.  The difference, of course, was that I could catch skippers with my net to see them up close.

One species that wasn’t difficult to identify was the regal fritillary.  Once I figured out how to tell the difference between regals and monarchs I started seeing regals everywhere.  In fact, when I helped with July 4th counts, regal fritillaries were usually one of the most abundant species we saw.  I didn’t realize until later how rare regals are in eastern prairie states, and how fortunate I am to live in Nebraska where their populations are still strong.

Regal fritillary butterflies are still common in many western tallgrass prairies and mixed grass prairies, but have largely disappeared from most eastern prairies.

As I learned more about the species and its conservation status, I saw some inconsistencies between what regals were thought to need for survival in eastern prairies and what our Platte River Prairies were providing.  For example, many people I talked to from the east told me that regal fritillary larvae needed prairie violets for a food source.  However, our Platte River Prairies – which are full of regal fritillaries – only have the heart-shaped-leaf blue violet (Viola pratincola), and no prairie violets.  In addition, plant species like purple coneflowers (Echinacea spp) that are heavily used as nectar plants by regal fritillaries aren’t present in the floodplain of the Central Platte River.  In 2010, with the help of Dr. Ray Moranz of Iowa State University, we started a research project to learn more about how regal fritillaries survive and thrive in our prairies.

Through the project, we’re investigating multiple aspects of regal fritillary habitat use – including nectar plant use, the use of remnant vs. reconstructed prairies, and the way in which regals interact with a landscape managed with a combination of fire and grazing.  We’ve only completed one field season so far, and will need more time to answer those questions, but we have already seen some very striking results in terms of nectar plant use.

To collect our data, we regularly walked transects through our prairies and counted butterflies – noting nectaring behavior when we saw it, and recording the species of flowers the butterflies were nectaring on.  I’m only referring to the nectaring data in this post because we’ve got more work to do to analyze the other data we collected.  It’s also important to remember that these are just pilot-year data, although they match what I and others have observed for many years.

Though we saw many hundreds of regal fritillaries on our transects, relatively few were actually nectaring.  Early in the season when numbers were highest, we saw mainly males – patrolling for newly emerging females.  When those females finally arrived on the scene we started to see nectaring behavior from both males and females, but observations of nectaring were still relatively rare.  Multiple years of data collection will be important to confirm the patterns we saw this first year.

There were really only two kinds of wildflowers that attracted the vast majority of nectaring regal fritillaries through the 2010 season, and both are usually called weeds.  The first was hoary vervain (Verbena stricta) and the second was a small group of thistle species – primarily Flodman’s thistle (Cirsium flodmanii) and tall thistle (Cirsium altissimum).  Hoary vervain is a native wildflower that is largely considered to be a pasture weed by many people because it thrives in overgrazed situations.  Cattle don’t like to eat it and it can spread quickly when the surrounding grasses are weakened.  (However, it also decreases in abundance very quickly when the grasses regain their vigor.)  Flodman’s and tall thistle are two native thistles that are also considered to be weedy plants, and that do well in overgrazed pastures.  The third favorite plant was actually several species of milkweeds lumped together (primarily weedy species like Asclepias syriaca and A. speciosa).

During the early part of the summer, the majority of regal fritillaries nectaring on flowers chose hoary vervain.

In late summer and early fall, vervain largely stopped blooming and other species became more important for nectaring, particularly native thistle species.

Most of our data collection centered on regal fritillaries, but we also collected data on other butterfly species.  So far, there doesn’t appear to be much difference in the nectaring preferences of regals and the larger butterfly community.  During the early part of the season, hoary vervain was the primary choice for most butterflies and a variety of other species got only infrequent visits.  Later in the season when hoary vervain was largely done blooming, thistles and a few other species, including wild bergamot – aka monarda or Monarda fistulosa and rosinweed (Silphium integrifolium), shared the load.

Observations of early summer nectaring across all butterfly species showed that hoary vervain was the dominant selection for nectaring.

Later in the season, other flower species split the nectaring observations fairly evenly.

One of the most interesting aspects of doing this research on butterflies has been that I’ve been able to look at our prairies through the eyes of butterflies – and that’s given me some surprising insights.  Our remnant prairies are largely degraded by years of overgrazing and broadcast herbicide use, and we’ve been working to slowly bring them back to higher floristic quality.  I’ve assumed that increasing floristic quality would also be good for many other species, including butterflies.  In addition, we’ve worked very hard at getting the highest plant diversity we can into our restored (reconstructed) prairies.  While we’re not restoring those prairies for butterflies, specifically, I’ve always assumed that butterflies would benefit from high plant diversity.  From our very preliminary data on butterflies, it appears that while our restored prairies have many more flower species, including many showy species, they may not be providing any better nectaring opportunities than our remnants!  The flower species most used by regal fritillaries and other butterflies are hoary vervain and thistles, which are at least as common in our remnants as in our restorations.

Regal fritillaries, and other butterflies, seem to rely heavily on hoary vervain for nectar in our Platte River Prairies.

I’m confident that there many other benefits of the plant diversity in our restorations, of course, including the availability of a variety of larval host plants for butterflies.  But it’s a little humbling – and intriguing – to see butterflies relying on plant species that do well in beat-up pastures rather than flocking to our showy restored prairies!  It’s important, of course, not to extrapolate these results to other parts of the country.  I’m not saying that regal fritillaries can survive in beat-up pastures in eastern states.  If that was so, we’d have many places in the east with lots of regal fritillaries.  Nebraska and other western states with high numbers of regal fritillaries also have landscapes with relatively high amounts of native prairie – and that may be the most important factor for regal fritillary survival.

The other lesson from our early data seems to be that the value of “weedy” species shouldn’t be discounted just because they thrive in conditions many flower species can’t take.  Vervain and thistles could be the primary plant species supporting our butterfly populations along the Platte River right now.  That’s a pretty good argument for being valuable.  In addition, the violet species that the regals must be using as a larval food plant along the Platte is considered to be relatively weedy because it does well in degraded pastures.  I’m sure glad we have a lot of it – and so are regal fritillaries!  Other weedy plant species have value as well – apart from their obvious role in filling space when “good” plants are weakened by fire, grazing, or drought.  The seeds of native ragweed and annual sunflower species, for example, seem to be excellent food sources for many small mammals and birds (judging from the density of tracks around the plants when it snows).

I’m really looking forward to next season’s butterfly transects.  I enjoyed reacquainting myself with butterflies last summer, and it was good for me to look at our prairie work through a different lens.  I’m sure we’ll learn more as we collect and analyze more data.  In the meantime, we (and our butterflies) will continue to enjoy and appreciate our weeds.

A big thank you to Dr. Ray Moranz for his assistance setting up this project.  Also, Mardell Jasnowski directed most of the data collection in 2010, with help from Nanette Whitten, Nelson Winkel, and Natalie Goergen.