People often seem surprised to learn that I’m an introvert – probably because in large groups, I feel pretty comfortable being the center of attention and talking to an interested audience. However, when I’m just one of many people in a large gathering, I naturally retreat to the edges of the group where I don’t feel hemmed in by humanity. As a result, during presentations out in the field, I tend to wander and explore while staying within earshot of what’s being said. I’m not trying to be rude, I’m just keeping my escape routes open…
Accordingly, two of the three mysteries I wanted to share today were things I found while skulking in the background during a tour last Friday at the Valentine National Wildlife Refuge. The first was a trailing wild bean plant (Strophostyles sp) with a series of intriguing holes in the leaves. I showed a couple other people, but none of us knew what might have made the holes. I’m guessing invertebrate, of course, but I don’t have any idea beyond that. It looks to me like something was rasping away at the surface of the leaf until it punched all the way through and then repeated the process in a new spot. Anyone recognize this?
Interesting holes in trailing wild bean leaves…
The second mystery relates to some piles of wild rose hip remains scattered around on the ground. We were standing in the middle of a good patch of wild rose and talking about how plants in recently burned areas (at least this year) seemed to have lots of large fruits. As I wandered around with my eyes scanning the ground, I spotted several places where some animal had apparently dismantled rose hips, leaving the skin (rind? husk?) and seeds strewn about on the ground.
Rose hip remains.
At first, I was wondering why an animal would go through the trouble to open up the fruit and then not eat the seeds or skin since there’s not much more to the fruit than that. Upon a closer look, though, it appears many of the seeds had been split in two, which makes me wonder if something was eating the center of the seeds and then spitting them out – almost like a ballplayer at a baseball game. I’m guessing this is a small mammal, but don’t remember seeing piles quite like this before. Help?
A closer look a the rose seeds, which seem to be split in half and hollowed out?
The final mystery was not something I discovered, but instead came from a question someone asked me. I feel bad, but I honestly don’t remember who it was who asked – I’d give them credit if I did because it was a great question. The question was, “Why don’t we see big flushes of annual sunflowers in the same place two years in a row, even when there is still plenty of bare ground?” We’d been talking about the hypothesis that plains sunflower (Helianthus petiolaris) germinates really well when there is abundant bare soil – such as after a fire or drought. However, the question asker rightly pointed out that it doesn’t seem like the same phenomenon repeats itself in the same location in the following year, even if those bare soil conditions still appear to be present.
Populations of plains sunflower, like the one our group explored in this burned patch of Sandhills prairie, don’t seem to flourish two years in a row, even when bare ground persists. There must be something else driving that population boom and/or restricting a subsequent one.
I don’t have an answer for that sunflower question. Possible explanations could include 1) the majority of the available seed bank germinated the first year and seeds from that crop need a year or more to become stratified or otherwise prepared to germinate; 2) sunflowers produce chemicals that inhibit their own growth the next year (seems doubtful); 3) an insect, microbe, or other organism builds up large populations during population booms of sunflowers and then either eats or infects seeds/plants of the next generation, preventing them from establishing. There are probably lots of other possibilities. Anyone have the answer?
I’ve said it many times, and it’s always true – finding these kinds of mysteries is what helps keep me interested and excited about prairie ecology. It’s fun to figure out the solution to the mysteries, but then I have to find more mysteries. Fortunately, there doesn’t seem to be any shortage of them!
The Prairie Ecologist 
The holes look like they are made by one of the leafcutter bees in the family Megachilidae.
Thanks as always for sharing Chris!
I was also going to suggest Leafcutter Bees. I released two batches of them at Prairie Pines and the notes with the bees said look for little holes in leaves just like in the photo. They chew the leaf and stuff them in the tubes I have in a native bee house. (Or some other place in the wild) to seal off and protect their eggs. (I purchase the Leafcutter Bees from Crown Bees.)
As always, I love your photos.
Pat Halderman
Rise hip mystery: my guess is a ground squirrel, mouse or bird…shelling it to eat the protein-rich seed inside.
Annual sunflower mystery: could exhaust local micronutrient that needs to build up support growth. Maybe nitrogen?
Doing a little reading on commercial sunflower production, some form of nitrogen is required, either fertilizer or rotation after soybeans or other legume, so perhaps exhaustion of soil nitrogen is indeed the reason why wild annual sunflowers tend not to grow in the same place, despite having bare soil…they need legumes or buildup of other organic material to provide sufficient nitrogen for growth.
Click to access sunflower_guide_69AF73CC348B6.pdf
There is an easy way to test your hypothesis. The year after sunflowers bloom abundantly spread a nitrogen fertilizer on a patch of prairie. This may cause the sunflowers to do an encore. However, it might just cause the grass to have more growth.
Hi Chris,
I completely understand the introvert situation. I do the same exact thing .
As for the Sunflowers, the same happens in my yard every couple of years, only with different varieties. Many have started from bird seed. Every Spring, they seem to migrate to another location , other years, I hardly have any. This year was amazing and it’s great to have so many pollinators and Goldfinches. Even a Common Yellowthroat visited.
The city of Omaha owns 1/2 of my back yard property that I have turned into a field of native Sunflowers, grasses and domesticated Sunflowers. It’s great to have a mini prairie out my back door in in such a busy area.
I’ve seen the rose hips in piles like you have. I’m thinking the ground squirrel likes those. I leave all the plants up all Winter and even tie the Sunflower stalks into teepees to provide a shelter for various critters.
I’ve learned much from you.
Thank you,
Karen K
The reason the sunflowers are doing this is predator satiation.
https://en.wikipedia.org/wiki/Predator_satiation
Here is a post by Stephen Packard about this behavior in compass plants.
http://vestalgrove.blogspot.com/2012/07/good-bad-and-odd.html
Safety in numbers can have survival benefits. This is something introverted prairie ecologists should consider before being too hasty at taking an open escape route. In contrast, new discoveries are only made by challenging the thinking of a group. I look forward to knowing the results of your experiment in the sandhills. Both the expected and unexpected.
I think the holes in the leaves may be from bean leaf beetles (Cerotoma trifurcata). The irregular shape and the location near the center of the leaf (rather than at the edge) seems atypical of leafcutter bees.
Thanks as always for the photos and mysteries!
I just looked at some photos of bean leaf beetle feeding patterns and I think you may be right Dan. The holes seem more irregular on the lower leaves and there may also be some “partial holes”. Great observation!
You aren’t alone, Chris – many of us naturalists are introverts, just as you described, but do very well in large groups where we are the center of attention. It is a dichotomy that confounds others.
Thanks for another good post.
Chris. I too am an introverted extrovert! I am often the center of attention, and yet at chit chat events I am totally out of my element and clam up. My wife and I met a fan of yours while hiking in the Maroon Bells area above Aspen, Co. Thanks for the tip and plant id help, Eric Siegel!
You’re opening paragraph describes me too! Perfectly happy to lecture to groups on botanical or horticultural topics but freak if any of the audience invite me to dinner!