Landscape Ecology of Singing Insects 1: Glacial Influences

by Carl Strang

One of my winter projects has been to write new sections for my singing insects guide which go into ecological topics. This was inspired by my reading a newly published textbook on landscape ecology (With, Kimberly A. 2019. Essentials of landscape ecology. Oxford University Press, Oxford, U.K. 641 pp). In the next few posts I will share parts of the added sections. Today’s focus is the impact of the last continental glacier on the landscape and selected insect species:

Though the focus in most of this guide is on the individual species of singing insects, the field of landscape ecology provides a framework of broader patterns and questions for which the ecologically diverse singing insects provide a suitable lens.

Landscape ecology considers geographical patterns and dynamics of their change across time. Any complete biological understanding of the Chicago region must include not only what is here now but also how it got that way. Fortunately, we don’t have to go back too far geologically speaking, as our landscape is less than 20,000 years old. Three major lobes of the most recent continental glacier flowed down from the North and scoured our region’s bedrock, then began their final retreat around 18,000 years ago. As the glacier melted, with occasional periods of stalling when the push from the North was balanced by melting at the edge, it left behind a variably deep layer of various kinds of deposits. The topography was more elevated in the morainal arcs where the melt was stalled for a time, lower and flatter when the melt-back was more uniform and rapid. Occasional pocks formed where blocks of glacial ice were buried and later melted, resulting in small lakes, bogs and other wetlands. Our rivers had their start as glacial meltwater drainage streams. The Lake Michigan Lobe of the glacier picked up and crushed the softer shale from the bottom of what was to become that lake, so it left behind deposits heavy in clay west and southwest of the lake. When glacial crunching and meltwater eroded harder igneous and metamorphic rocks the ice had transported from Canada, gravel and sand resulted. Quartz sand, the most erosion-resistant component of such rocks, accumulated especially around the edge of Lake Michigan and the tributaries of the Kankakee River, which started as a glacial meltwater drainage stream originating in the part of the region covered by the glacier’s Saginaw Lobe.

This glacial history impacted our singing insect fauna in various ways. Some species require, or at least are only abundant, on sandy soils. These include the green-winged and northern dusk-singing cicadas, whose nymphs live on buried plant roots, and some of the grasshoppers, for which the sandy substrate for egg-laying and/or a poor-soil plant community is an important habitat component. A couple of species, the gray ground cricket and the seaside grasshopper, are limited to the beaches and dunes around the Lake Michigan edge.

The beaches at different points on the Lake Michigan shore have different compositions, resulting in selection for different colors in the seaside grasshopper. Here, at Illinois Beach State Park, there is a greater mix of different colors of ground igneous and metamorphic rocks.

The beaches of the Indiana Dunes are a more uniform quartz sand. Here, two seaside grasshoppers (same species as in the previous picture) would be nearly invisible if they were not flashing their inner femur colors at one another.

Kames are gravel hills formed by waterfalls within the melting glacier, and they provide a well-drained substrate. Isolated populations of sulfur-winged grasshoppers and tinkling ground crickets live on a kame in the Lulu Lake Nature Preserve in northern Walworth County, Wisconsin.

Exposed gravel on part of the kame at Lulu Lake.

All species were pushed south by the glacier, surviving in what is now the southern U.S. and being influenced by selective forces then and during the advance north as the climate moderated and plant communities spread back over the barren glacial deposits. Most of our familiar prairie and forest plant species were restricted to rather small refuges in the South during the glacial maximum, though oaks and hickories occupied a large part of the southern U.S.

Black oak savanna, Kankakee County

As the glacier melted back, open sedge tundra with some black spruce trees invaded first, then white spruces filled in to form a recognizable northern coniferous forest until around 15,000 years ago. By around 12,000 years ago most of our landscape was a mix of deciduous species, including woodlands with lots of oaks. Beginning around 10,000 years ago there was a drying period, which led to the spread of prairie through our area. The prairie then retreated as the climate became wetter, so that by 6200 years ago the western part of our region was a prairie with islands of woodlands and wetlands, grading to forest in the eastern part. This reflects a gradient of increasing moisture from west to east, mediated by the flow of wet air circulating north from the Gulf of Mexico. The drier prairies were maintained by fires which frequently knocked back woody plants that otherwise would have converted even the western part of the region into woodlands. The wooded islands within the prairie were not randomly located, but survived where rivers, other wetlands, and topographic breaks shielded certain spots from prairie fires pushed by the prevailing westerly winds. The upshot for our singing insects is a diverse landscape that to this day contains species specializing in prairie, woodland and various wetland habitats, as well as some that thrive around the edges between habitat types. A few species may be relicts of earlier changes in this history. For instance, the delicate meadow katydid, now apparently extinct in the region, is abundant in prairies to the west and probably accompanied the prairie advance. By the early 20th Century it was known in a very few scattered locations. I have not been able to find it anywhere in the present day.

Delicate meadow katydid females have longer ovipositors than their close relatives.

Latitudinal Gradient

by Carl Strang

One of the classical challenges of community ecology is the latitudinal gradient of species diversity, species counts diminishing from the tropics to the poles. The observation is easy to make and applies across practically the entire range of species groups. Many theories have been proposed to account for this pattern, and probably some combination of factors is at play. It never had occurred to me to see whether the gradient applies across the relatively narrow latitude range of my Chicago region survey area for singing insects.

One addition to the next edition of my regional species guide will be an expanded introductory section on range extensions, along with new sections on landscape ecology and community ecology. As I drafted that material, it occurred to me that I might check for latitudinal changes in species counts.

It turns out that the pattern appears in the region’s 6 rows of counties. From south to north, median species numbers are 60, 60.5, 57, 53, 44.5 and 43.

St. James Farm Update

by Carl Strang

It has been a while since I have written about St. James Farm, where I volunteer as forest steward and monitor. There has not been a lot to report, in part because foot problems have limited my monitoring activity.

Going back to last fall, I noted that the patches of invasive goutweed where we dumped garlic mustard showed a difference. One patch, which had not been hit by herbicide in the spring, pushed its way through the mounds of wilting garlic mustard and was barely slowed.

Other patches like this one, which forest preserve district staff had sprayed earlier in the spring, appeared to be inhibited further by the dumps.

I noted that goutweed does not maintain winter rosettes, but withdraws nutrients into the roots and shuts down the leaves, growing new ones in the spring. This coming fall I plan to hit experimental patches of goutweed with herbicide, with the idea that I might find an optimal time when the poison, drawn down along with the conserved nutrients, will do the most damage to those invasive plants.

Through the winter I took series of monitoring walks twice a month. There was little that was new.

Predators took their tithe, in this case pulled feathers spoke of a male eastern bluebird caught by a raptor.

This buck was one of a group of three that occupied the western part of the forest through the winter.

Though I cut back on monitoring efforts, Wednesday morning restoration activity continued. Our focus through the winter consisted of cutting and stacking common buckthorn, then burning the piles.

Our earlier cutting accumulated 17 piles like this.

Burning them leaves relatively small scars, but the soil is sterilized. I will be interested in seeing what plants invade these little spaces.

Already we have built several new piles. There won’t be enough snow to allow any more burning now, but by next winter there will be plenty to torch.

My feet are under treatment, and I expect to return to full activity soon.

 

Where There’s Smoke

by Carl Strang

Mid-November brought forest preserve district crews to St. James Farm to conduct controlled burns in the forest. These burns are a normal part of oak woodland ecology in northeastern Illinois, and they help control invasive plants. Occasionally the consequences of the burn extend beyond the brief time when the flames consume the dry leaf litter on the ground, and I noted two such incidents this time around.

Carpenter ants commonly hollow out the base of a tree as they tunnel through the dead wood at the core. If the accumulated sawdust catches a spark from the controlled burn, a slow growing smoldering coal can expand to the point where it consumes a significant amount of the remaining wood.

A victim of that phenomenon was the large white oak that harbored the great horned owl nest last winter.

A victim of that phenomenon was the large white oak that harbored the great horned owl nest last winter.

There had been a larger live stem, and a smaller dead stem (the fractured one in the photo) where the nest had been. The live stem’s base was thinned by the growing coal to the point where it went down, taking the nest stem with it.

The same burn had the remarkable effect of catching in another tree, already knocked down by a storm, which then smoldered for weeks.

Here is the tree 2.5 weeks after the burn, on December 5. The underside of the fallen stem was burning slowly from west to east, and the top of the stem protected the coal from the snowfall.

Here is the tree 2.5 weeks after the burn, on December 5. The underside of the fallen stem was burning slowly from west to east, and the top of the stem protected the coal from the snowfall.

Another heavier snowfall still did not stop the burn, here on December 12. This was a cold day, but a moderate west wind kept the coal alive.

Another heavier snowfall still did not stop the burn, here on December 12. This was a cold day, but a moderate west wind kept the coal alive.

At that point, however, the coal was no longer sheltered. When I returned on the 16th, I found the fire had gone out. It had lasted nearly a month.

 

Exploring the Interior

by Carl Strang

Now that the leaves are down from the trees and shrubs, I have been exploring the areas between the forest trails at St. James Farm Forest Preserve. Those areas are large enough that I cannot cover the forest adequately from the trails. I have found deer runs and old equestrian paths that will provide sufficient access for routine monitoring. Along the way I have found some interesting places. One foggy day I zig-zagged my way through part of the western forest.

This area has been cleared of invasive honeysuckles and other shrubs. Part of it is young second growth with a few clearings where perennial herbaceous plants are growing.

This area has been cleared of invasive honeysuckles and other shrubs. Part of it is young second growth with a few clearings where perennial herbaceous plants are growing.

Elsewhere there are old trees, many of them red oaks.

Elsewhere there are old trees, many of them red oaks.

Among the occasional boulders was this outwash-rounded fossiliferous one.

Among the occasional boulders was this outwash-rounded fossiliferous one.

The chunk of local Silurian dolomite appears to have been a spot on the ocean floor, adjacent to a reef, where there was a crinoid colony.

The chunk of local Silurian dolomite appears to have been a spot on the ocean floor, adjacent to a reef, where there was a crinoid colony.

A morainal depression held a huge fallen red oak.

A morainal depression held a huge fallen red oak.

The tree had lost the grip of most of its roots in the soil.

The last roots that were holding the tree up still show the relatively fresh color where they fractured.

The last roots that were holding the tree up still show the relatively fresh color where they fractured.

The orientation of the trunk relative to those broken roots suggests that a very strong wind from the west was the culprit.

 The oak didn’t go down alone. Broken stems reveal the trees it took out on either side. The force of the fall split the oak’s stem lengthwise.

The oak didn’t go down alone. Broken stems reveal the trees it took out on either side. The force of the fall split the oak’s stem lengthwise.

Each day in this exploration has brought its own delights.

Here, a beautiful moss colony became established on an old burn scar.

Here, a beautiful moss colony became established on an old burn scar.

One day when I was the preserve’s only human visitor, I saw one of St. James Farm’s coyotes. The fat belly and good coat indicate that this animal is a successful hunter.

One day when I was the preserve’s only human visitor, I saw one of St. James Farm’s coyotes. The fat belly and good coat indicate that this animal is a successful hunter.

So now the stage is set for routine coverage of St. James Farm’s ongoing natural history story.

 

First Snow

by Carl Strang

Our first winter storm of the season was worthy of the name, with 24 hours of occasionally heavy snowfall and strong winds. Even after some of the first snow melted in contact with the ground, St. James Farm Forest Preserve ended up with 3-6 inches on the ground. On Sunday I took an extended walk through the northern, forested portion of the preserve.

I wasn’t alone. Many hikers, skiers and snowshoers took advantage of the fresh snow.

I wasn’t alone. Many hikers, skiers and snowshoers took advantage of the fresh snow.

The wet snow stuck to the vegetation.

The wet snow stuck to the vegetation.

Herbaceous plants bowed under the weight.

Herbaceous plants bowed under the weight.

The smaller birds were challenged to find food through this obstruction. The temperature was cold enough to freeze shallow ponds.

This pond is hidden in the northwest corner of the woods.

This pond is hidden in the northwest corner of the woods.

This was my first opportunity to get an overview of mammal activity across the preserve. The absence of cottontail tracks perhaps was the biggest surprise. The more open southern part of the preserve, which I did not check, is more suited to them.

I saw only one set of opossum tracks, but would not expect much activity from them under the conditions.

I saw only one set of opossum tracks, but would not expect much activity from them under the conditions.

White-footed mice are abundant in the forest.

White-footed mice are abundant in the forest.

Coyote tracks showed a thorough coverage of the area overnight.

This footprint was made soon after the main snowfall ended. Ice crystals formed within it afterward.

This footprint was made soon after the main snowfall ended. Ice crystals formed within it afterward.

A pair of coyotes hunted together for a time.

A pair of coyotes hunted together for a time.

Though the disruption of the rut makes any pattern temporary, I was interested in assessing deer activity as well.

A few individuals crossed Winfield Road between St. James Farm and Blackwell Forest Preserves.

A few individuals crossed Winfield Road between St. James Farm and Blackwell Forest Preserves.

Half a dozen deer moved together at one point. The main activity was in the western portion of the woods, with almost all movement trending east-west. Only a couple deer, moving north-south, left tracks in the eastern portion. All of this is subject to change when things settle into the winter pattern over the next month.

 

July Flowering Phenology

by Carl Strang

July was the last month in which I collected phenology data from Mayslake Forest Preserve. The results provided a satisfactory conclusion.

Many of Mayslake’s prairie plants first open their flowers in July.

Many of Mayslake’s prairie plants first open their flowers in July.

First flower dates become less different among years as the summer progresses, and that was true this year as well. The median difference from 2014 was 0 days for 47 species, an insignificant 2 days earlier than in 2013 for 31 species and the same vs. 2011 for 37 species, 1 day later than in 2010 for 37 species, and a slightly larger 5 days earlier for 35 species in comparison to 2009. The odd early year of 2012 continued to be the outlier, but even that difference was down to 10.5 days for 38 species.

Michigan lily provides one of the preserve’s more extravagant floral displays.

Michigan lily provides one of the preserve’s more extravagant floral displays.

All those medians were smaller than those for June, except the one for 2013, which was the same.

 

Pocket Prairie

by Carl Strang

This is the time of year when the view out my back window is best.

The diversity of blooming wildflowers hits its peak in late July.

The diversity of blooming wildflowers hits its peak in late July.

My neighborhood for the most part is a wildlife desert. It’s amazing what a little habitat can bring, though. These native prairie flowers attract diverse pollinators, and bumble bees for instance always are present in the daylight hours. The red blooms are royal catchflies, which never fail to bring hummingbird visitors in July and August. Later, goldfinches will be after the seeds in the purple coneflower heads. My original planting plan is history, as most of these plants are seeding into the tiny spaces left between. My main work has shifted from planting to thinning, keeping the better competitors at bay so as to maintain a balance of biodiversity. That makes me a member of this community, too.

June Flowering Phenology

by Carl Strang

First flower dates at Mayslake Forest Preserve in June continued the trend of convergence on earlier years that is typical of the progressing season. The median difference from 2014 for 71 species was only one day earlier, and two days earlier than 2013 for 69 plant species.

Butterfly weed was among the species that first opened flowers in June.

Butterfly weed was among the species that first opened flowers in June.

The biggest difference continues to be with the very early year of 2012, but that is down to a median of 11 days later for 71 species. The difference for the remaining three years is not large: 5 days earlier than 2011 for 61 species, 5 days later than 2010 for 49 species, and 6 days earlier than 2009 for 51 species.

Compass plants began to bloom just before the end of June.

Compass plants began to bloom just before the end of June.

These differences represented reductions of 6 days, 3 days, 7 days, 1 day, and 4 days from May values for the years 2014-2010. The difference for 2009 increased by 3 days.

May 2015 Phenology

by Carl Strang

April’s phenological signal held true in May’s first flowering dates. This year continues to run ahead of most, but not by much.

Ohio buckeye was among the plants that bloomed in May.

Ohio buckeye was among the plants that bloomed in May.

Median first flower dates this May at Mayslake Forest Preserve were 7 days earlier than last year (54 species), 5 days earlier than in 2013 (70 species), 18 days later than in 2012 (69 species), 4 days earlier than in 2011 (68 species), 7 days later than in 2010 (45 species), and 3 days earlier than in 2009 (46 species).

Common spiderwort is peaking now, but started blooming in May.

Common spiderwort is peaking now, but started blooming in May.

The respective numbers for April were, in the same order: 6 days earlier, 9 days earlier, 25 days later, 6 days earlier, 9 days later, and 3 days earlier. On the whole this shows the usual trend of convergence among years as the season progresses.

A number of sedges first bloomed in May, including the small yellow fox sedge.

A number of sedges first bloomed in May, including the small yellow fox sedge.

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