Looking out your window on a sunny day you’ll notice the different shrubs, trees, birds, and possibly a rabbit in your yard. And when you go for that hike in the park, there will be untold insects, maybe a frog, snake, or salamander. And of course, you can’t forget the wonderful morning smell of the skunk that passed through last night, or the deer quietly grazing in a neighbor’s meadow.
What you just experienced in a small way is the variety of life inhabiting the Earth – the biological diversity, or biodiversity, of nature. Biodiversity underlies everything we do as Master Naturalists.
At our last members meeting, Amy Johnson, the Director of Virginia Working Landscapes, discussed various biodiversity studies her group is involved with, pointing out some of the ways that scientists (and citizen scientists such as Master Naturalists) study biodiversity and its implications.
Scientists, however, have long debated how to precisely define and measure biodiversity. Is it the number of species? Is it the number different functional roles being fulfilled by various species in an ecosystem? Is it the genetic diversity in a population? Is it the diversity of ecosystems and how species come together in different assemblies?
The table below shows some of the many elements and dimensions that scientists consider when studying and measuring biodiversity:
The figure below shows another way of looking at biodiversity. Notice the three “standard” ways that scientists typically look at biodiversity – genetic diversity, species diversity, and ecosystem diversity – and some of the alternative ways – compositional diversity, structural diversity, and functional diversity.
Source: P. Duelli, M.K. Obrist / Agriculture, Ecosystems and Environment 98 (2003) 87–98
By now you’re getting the sense that biodiversity is much more than the “variety of life.” In some respects, trying to define it is akin to the parable of the blind men and an elephant. In other respects, it depends on what you are studying – local habitats, food webs, a particular species, or a larger landscape or region. For example, a study of a local habitat or niche may focus on biodiversity as the number of different species in that habitat or the genetic variation of the resident populations.
If the scale of the study is larger, say a watershed, landscape, or larger geographic region, the focus may be on the diversity of community assemblies or ecosystems present. Studies of food webs likely will focus on the diversity of functions different species perform.
These different perspectives on biodiversity (species, functions, communities) are also not independent of each other, but interrelated.
A formal definition that attempts to encompass these various dimensions of biodiversity is the 1992 Convention on Biological Diversity, an international agreement among 150 nations, which defined biodiversity as:
“…the variability among living organisms from all sources including, [among other things], terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are a part; this includes diversity within species, between species, and of ecosystems.”
This definition recognizes biodiversity as including genetic diversity, species diversity, and ecosystem diversity, among other dimensions and elements.
How is Biodiversity Measured?
It will come as no surprise that given the complexity of the biodiversity as a concept that there is not a single measure for biodiversity. Most biodiversity measures have two basic components – some measure of the number of entities present and some measure the degree of difference between those entities. For example, biodiversity can be measured by the number of species in a specific area, using such metrics as species richness (how many distinct species in an environment), or metrics such as evenness (how close in numbers each species in an environment is), rank abundance (relative species abundance), and various other species diversity indices, such as the Simpson Index or Shannon Index, that capture the degree of difference between species in a sample. Endemism richness is another type of biodiversity measurement that focuses on the proportion of rare, locally occurring endemic species. The field of biodiversity measurement is a subject that can cover several graduate courses in ecology.
To illustrate the problem of measuring biodiversity, look at the illustration below - which of the two areas below do you consider to have a higher biodiversity?
The two areas have the same number of individuals (20). The area on the right has more species (8) (species richness), but the ecosystem on the left has greater evenness across species as reflected in a higher Shannon Index. The Shannon Index quantifies the uncertainty in predicting the species identity of a random individual (i.e., the less difference there is among species, the greater evenness). As the Shannon index approaches zero, species differences approach zero (monoculture), hence a larger Shannon Index number is indicative of greater the biodiversity. The two areas might also be compared based on endemic richness. For example, if the ant, beetle, and frog in the right ecosystem were endemic species to that particular local area, then the ecosystem on the right might be considered more biodiverse and worthy of conservation.
Biodiversity also might be measured by the variety and number of different functions that species fulfill in an ecosystem, such as primary producers, herbivores, and carnivores. Functional diversity can be measured in a number of ways (Laureto, et al., 2015; Song, et al., 2014). One way is by the complexity and connectivity of a food web and the functional roles in the food web. In Figure 2, functional diversity on the right side would likely be different from the left side (e.g., the right-side area, populated by frogs, beetles, and ants in a pine forest would likely produce different functions and food web structure than the left-side area dominated by crows and salamanders).
Apart from species and functions, biodiversity might also be characterized by the degree of ecosystem diversity. Ecosystem diversity is the largest scale of biodiversity measurement, and within each ecosystem, there is a great deal of both species and genetic diversity. In Figure 2, one could study biodiversity by comparing the differences in communities and species assemblies between the left and right side “ecosystems”.
An example of ecosystem diversity is the Southern Appalachian region—stretching from West Virginia and southwestern Virginia to northern Alabama. This region has a number of diverse ecosystems which contributes to the area’s high biodiversity.
Fun Fact: Virginia has over 3800 species, including the third-highest number of amphibian species, and the 13th highest number of vascular plant species in the United States.
Within this region, Virginia has a variety of physiographic areas—from western mountains and valleys, to rolling hills, to Tidewater estuaries— that provide many habitats supporting a wide variety of ecosystems. For example, the Clinch Mountain Wildlife Management Area—covering about 25,000 acres in Russell, Smyth, Tazewell, and Washington counties—is considered to be Virginia’s “most biologically diverse [management area], due in large part to the vast differences in elevation on the area” and is particularly known for the diversity of fish and mussels in the area’s watersheds. On the other side of the state, the aquatic ecosystems and wetlands of the Chesapeake Bay and Virginia’s southern coastal environments are sites of significant biodiversity.
Master Naturalists and Biodiversity
As a Master Naturalist, you are involved with biodiversity at every turn. Stream monitoring and water quality assessments are based on sampling the macro-invertebrate species richness found in a particular reach of a stream. Butterfly surveys record the number and differences in species found in a local area. Volunteer work on native plants, pollinator gardens, and habitat restoration is fundamentally aimed at supporting greater biodiversity. Feeder Watch and the Great Backyard Bird Count help assess the diversity of local bird populations. And that ubiquitous invasive plant removal projects, and more recently our work with Spotted Lanternfly monitoring, are aimed at threats to biodiversity. I am hard pressed to think of any project we undertake as Master Naturalists that is not tied either directly or indirectly to biodiversity.
There are a number of resources you can use for further insights about biodiversity – some our listed below in further reading and references. Also, on the ORMN website there are blogs, science research, news articles and other resources on various aspects of biodiversity.
In the next installment of this series, we’ll travel back in time a few hundred million years to see how biodiversity has waxed and waned over the millennia. Until then, get out and enjoy the variety of life around you!
The Diversity of Life, by Edward O. Wilson (1992, Harvard University Press)
The Invention of Nature: Alexander Von Humboldt’s New World, by Andrea Wulf (2016, Knopf)
Evolution: The Triumph of an Idea, by Carl Zimmer (2006, Harper Collins)
Duelli, P. and M. Obrist, (2003). Biodiversity indicators: the choice of values and measures, Agriculture, Ecosystems and Environment, 98: 87-98.
Gaston, K.J. and Spicer, J.I. (2004). Biodiversity: An Introduction, Blackwell Publishing, 2nd Edition
Laureto et al., (2015). Functional diversity: an overview of its history and applicability, Natureza & Conservação, 13(2): 112-116, doi.org/10.1016/j.ncon.2015.11.001.
Ecosystems and Human Well-Being: Biodiversity Synthesis, by The Millennium Ecosystem Assessment (2005, World Resources Institute)
Mora, C.; et al. (2011). "How Many Species Are There on Earth and in the Ocean?". PLOS Biology. 9 (8): e1001127. doi:10.1371/journal.pbio.1001127.
Song et al, (2014). Relationships between functional diversity and ecosystem functioning: A review. Acta Ecologica Sinica. 34: 85–91. Doi: 10.1016/j.chnaes.2014.01.001.
Tilman, David (2012). Biodiversity and Environmental Sustainability amid Human Domination of Global Ecosystems, Daedalus, 141(3): 108-120, Summer 2012.
 The parable is a story of a group of blind men who have never come across an elephant before and who learn and conceptualize what the elephant is like by touching it. Each blind man feels a different part of the elephant's body, but only one part, such as the side or the tusk. They then describe the elephant based on their limited experience and their descriptions of the elephant are different from each other.
SERC: Landscaping for Biodiversity: A plant-insect perspective
Also, please find additional resources provided by Dr. Burghardt:
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