B. LIFE IN A MICROHABITAT

The magnificent ox beetle uses leaf litter in an unusual way. After digging a deep burrow (about 20 cm) in the sand, the beetle fills the bottom with dead oak leaves and lays an egg. After the egg hatches, the larva feeds on the dead leaf compost. Parts of a Beetle Several kinds of crickets live in leaf litter. In Florida scrub, the most common cricket is the painted ground cricket, which is dark brown with bright, cream-colored trim on the head and wings. The males sing day and night during much of the year. Their quiet songs blend into the background, like the ticking of a clock, and are a part of Florida scrub's atmosphere that few people notice. Not all species of Florida cockroaches like kitchens and garages. The leaf litter of Florida scrub is home to several species. Because they scurry away quickly at the slightest disturbance, they can be difficult to find. Biologist know that these scrub cockroaches, when observed in the lab, will eat almost anything from dry oatmeal to peanut butter sandwiches. However, the natural diet of these roaches out in the scrub is not known. Scrub cockroaches are eaten by lizards, spiders, and several species of wasps.

Introduction

If you look at the Florida scrub landscape through a camera lens, you will see areas of bare sand and patches of ground covered with brown, decaying plant parts. If you zoom in for a closer view of the brown leaf cover, you will see lots of plant parts such as dead leaves, pine needles, acorns and parts of acorns, grass stems, twigs, branches, chewed pine cones, and bark. This dark mix of dead plant material is home to an amazing number of organisms. You won't see many of these animals, even if you pick up or kick the debris around with your foot. But by using traps especially designed by entomologists to find small creatures in leaf litter, your class will discover a very populated, diverse world of animals that they have probably never seen before.

In this section, your class will make several simple traps to investigate leaf litter and catch a variety of insects and non-insect arthropods. The results will confirm---life among the dead leaves is more complex and fascinating than you'd ever imagine!

Background Information

Scientists have identified well over a million kinds of plants and animals-and more than half of these are insects! This vast variety and abundance of all kinds of living organisms is referred to as biodiversity. Some habitats have a greater biodiversity than others. For example, a forest has more biodiversity than your yard and your yard probably has more biodiversity than an orange grove! The biodiversity of a habitat frequently reveals how healthy it is. A lower biodiversity often indicates that a habitat no longer has the space, food, or shelter needed to support a variety and abundance of organisms or it may signify other environmental problems.

Even in healthy Florida scrub, the biodiversity is not as great as you might expect. The harsh conditions of scrub are impossible for many organisms to endure. Only plants and animals specially adapted to dry, hot sandy conditions can survive. However, the more protective conditions of the leaf litter make this microhabitat within the scrub appealing to a variety of organisms. Therefore, the diversity of organisms in scrub leaf litter will often be greater than the diversity in the dry, open sandy patches of scrub.

Biologists also use the term species richness to describe the variety of organisms found in an ecosystem, habitat, or microhabitat. The species richness of scrub leaf litter is impressive. The decomposition of dead plant material is tough work and it takes many creatures with different "skills" to get the job done. Although the final breakdown of decaying plant material is completed by bacteria and chemicals, the dead material is broken down much faster if it gets chewed up first. Many different species of arthropods such as millipedes, pillbugs, and caterpillars consume dead leaves while eating a bacterial film or threads of fungi that invade leaf litter. You will capture some of these leaf-eating organisms during this activity.

Many of the arthropods found in leaf litter have dark and/or neutrally-colored exoskeletons that allow them to easily hide from predators such as the eastern towhee. Hard, outer wing covers called elytra protect a beetle's hindwings and abdomen and are a useful adaptation in the close quarters of the leaf litter. Other insects in the leaf litter, such as the pillbug, protect themselves from predators by rolling up or "playing dead."

When you collect your leaf litter and examine your catch, you will probably discover that the organisms found in one batch of leaf litter may be quite different from those found in other samples collected just a few feet away. Leaf litter and the surrounding environs create separate microhabitats. And because conditions vary from one microhabitat to another, the animals that live in them will vary, too. For example, leaf litter found under a scrub oak will provide different physical and biological conditions to organisms than leaf litter dug out of a tree stump or grass clump. You may find more pill bugs in leaf litter and more termites in a dead log.

When you go out with your students to examine leaf litter, the multitudes of species you encounter may be a bit overwhelming. The names of the species are not important, but the biodiversity is. It is important to know that there are great numbers of species, and their combined activities keep our world in balance. They purify air and water, they recycle the nutrients that would otherwise be lost from the system, they keep pest species in check, so, for example, we almost never need to use pesticides when growing pine trees in Florida. The services performed by natural systems do not depend on a few key species. They depend on thousands of species. In a similar way, we may think of our bodies requiring a few key chemical compounds to function well: carbohydrates, vitamin C, certain amino acids, etc. In actuality, we depend on thousands of chemicals, most of them produced inside our own system, in order to function well. Ecological systems are more flexible and less easily disrupted than our own physiological systems, but both kinds of systems depend on diversity. Many students today spend almost all their time in habitats with hardly more biodiversity than their classroom. They have no idea of the biodiversity of the systems that sustain humanity. These students might know a lot of technology, but the ecological world that they depend on might as well be run by magic. This might not matter, except that we already have the power to change the world so that its ecology is disastrously simplified. By the time these students are adults, the power of our species will be even greater, and require even more judgement and responsibility.