Introduction to Biogeography and the Human Dimensions of Global Change:Background Information

Note: hot linked bold face terms are in the Glossary

Introduction

When you first picked up this text and read the title "Living in the Biosphere: Production, Pattern Population, and Diversity," did you wonder what this "biology topic" had to do with geography, let alone with the human dimensions of global change? If you did, you just asked yourself one of the most relevant and interesting questions in global change research! This first unit tries to explain why geographers are interested in processes occurring in the biosphere. What are they looking at when they speak of the "human dimensions of global change?" and in what ways do the biospheric studies overlap with, or contribute to, the study of the human dimensions of global change? The answers to these three questions will provide the framework for this module.

What is the Biosphere? What is Biogeography?

Let us begin with clarifying what is meant by the term biosphere before we get into the questions posed above. The biosphere is the totality of all regions of the earth that support ecological systems, or more simply put: all those regions on the planet that support and are affected by life. The biosphere is made up of parts of the atmosphere (air), the hydrosphere (the realm of water), and the lithosphere (the solid portions of the earth, rocks).

So, "Why are geographers interested in the processes occurring in the biosphere?" First of all, not all geographers are. There are really two kinds of geographers that are interested in the biosphere, one more directly than the other. The members of the first group would call themselves "biogeographers" because they look at the biosphere through geographical "glasses." We'll come back to that below. The other group, which is more broadly and more loosely defined, is made up of those geographers whose work falls into the nature-society tradition within geography. These geographers study not the biosphere per se, but the two-way interactions between humans and their environment. We will come back to this as well when we look at the human dimensions of global change.

If we had to draw lines between the subject areas of biologists, ecologists, and biogeographers, they would be rather blurry ones. You can think of it as dividing up the "biosphere cake" among these three (and maybe some others), yet once in a while one of them would grab a bite from the other one's plate. Biogeographers share with biologists and ecologists the effort to compile inventories of organisms; biogeographers share with ecologists in particular the search for understanding the interactions among organisms and between organisms and their environments, even though biogeographers probably focus more on the latter type of interaction. And biogeographers, perhaps more than the other two, are interested in the distribution of organisms. What distinguishes biogeographers from biologists and ecologists is their propensity to look at inventory, interactions, and spatial distributions at different geographic scales. Biologists and ecologists focus more on the population, organism, and suborganismic levels, whereas biogeographers usually start at the population level and go to the global scale. One could argue that biogeographers must move from one scale to another if their overarching goal is to understand why species occur, in the way they do, where they do.

The Human Dimensions of Global Change

Global change is probably not a new phrase for you. For years now, people have been speaking about global climate change and global warming -- to name but two common examples. But "global change" really means something much broader than what these two examples indicate. The term refers to changes in the environment more generally. Oh yes, you might say, I have heard of some others: deforestation, desertification, soil erosion, loss of biodiversity, acid rain, ozone depletion (another climate example). All of these are excellent examples of global environmental changes. And yet, the term is even broader.

The examples given so far all imply human interference with the natural environment. This is one important dimension of global change, and it is what we will be concerned with later on in this module. Yet it is essential to understand -- not only in order to place the human dimensions of global change into the larger global change agenda, but also to understand some of the difficulties and controversies in global change research -- that global changes can be entirely "natural," i.e., they can occur without the interference of humans. Examples of entirely natural changes are climate changes stemming from variation in the intensity of sunlight that we receive; geologic events or processes with global impacts, such as major volcanic eruptions or continental drift; and species extinction as a result of such solar/climatic and/or geologic processes. Global changes are usually the combined result of "natural" and human causes, and often we don't know to what extent change is due to one or the other.

For most of the 1970s and 1980s, global change research (even if it acknowledged or assumed human causality) focused on the physical dynamics of global change. Since the mid-1980s social scientists have highlighted the need for research on what they call the human dimensions of global change. There are three basic human dimensions, each one of which, when unwrapped so to speak, has many additional facets and components to it:

This brief overview of the human dimensions of global change suggests why geographers can make considerable contributions in this area: the questions researchers ask about the human dimensions of global change deal -- in one way or another -- with the interactions between humans and their environment.

How Does Biogeography Relate to Human Dimensions of Global Change Research?

Thus far, we have unquestioningly accepted the common perspective that distinguishes between a natural world and a human(-made) world. We maintain this general distinction throughout the module, yet we should be aware that some scientists don't draw such a sharp line between the two. For example, from an ecological and/or biogeographical perspective, humans may be viewed as just another species. There is no unanimous agreement whether one of these perspectives is better suited than the other to understanding the dynamics and implications of global change. More likely, each perspective has its merits for some of the questions, but not for others. You might want to think about this for yourself.

We forgo this discussion and instead focus on how biogeographic research relates to research in the human dimensions of global change. If we create a mental overlay of the previous two sections, we can see that biogeography contributes to our understanding of the human dimensions of global change and vice versa in several ways.

Biogeography, as mentioned earlier, attempts to understand the factors that contribute, and the processes that lead, to the variability in geographic distribution patterns of ecosystems and populations of organisms, the variability in productivity and biodiversity at various scales, and to variations in reproductive patterns. The factors and processes may be entirely natural, or (as is more likely the case today) they may be influenced by human interactions with the environment. Biogeography thus contributes to our understanding of the causes of global change in tackling the difficult task of separating human from non-human influences. It also contributes to our understanding of the impacts of global change in grappling with concepts like the fragility, sensitivity, and resilience of different kinds of ecosystems in the face of disturbance. Biogeography also attempts to establish qualitative and quantitative causal linkages between human interference (driving forces) on the one hand, and changes in the natural environment (changes and impacts) on the other. This is an enormously important area of research as both the human and the natural world are extremely complex and interconnected in many ways that are often invisible or intangible. Research on the links between driving forces and environmental change must consider feedback loops between human actions and ecosystem response and vice versa.

Another important aspect is that biogeographers as well as global change researchers work at various scales: from the local to the global. Although we speak of "global changes," we need to remain mindful of the fact that the actual processes that lead to change occur locally and then either accumulate to cause change that is global in scope (cumulative change) or fundamentally change the spheres of the earth (such as the atmosphere, the biosphere, etc.) systematically (systemic change). In fact, the module focuses mostly on what will be called here the "process scale," that level at which the actual changes in the biosphere occur.

A final area in which global change research overlaps with biogeographic research is in the methods each uses. Both engage in field studies, in historical analyses of biogeographical changes in response to human interference (e.g., through the investigation of geologic records), and -- of increasing importance -- in simulations (in particular, computer-based modeling) of "what-if " situations, i.e., of possible future states of the natural environment.

In this module, we cannot deal with all these areas of overlap, which include themes, scales, and methodology. Instead, this module will focus on the following:

Main themes: productivity at various scales;
natural variability in the geographic distribution patterns of biomes;
biodiversity at various scales
Secondary themes: qualitative and quantitative (causal) linkage between human interference and changes in the natural environment
Methodology: simulation (computer modeling) of what-if/future situations
Scale: biome>> ecosystem>> species>> individual organism (process level)>> and back to the biome level.

The remainder of the module is divided thematically into units on production, patterns, and diversity. The secondary theme of human-environment interactions and scale issues resonates throughout these units. In the activities associated with the units, we will -- among other things -- actually try some simulations. But first, let's turn to some basic concepts of ecology and of doing research, so that we understand the technical terms used in later units and better see how the units relate to each other.

Some Basic Concepts of Ecology and Science

Ecology is the science of the mutual interactions between organisms and their environments, and of interactions among organisms. These interactions are enormously complex and the aspect of mutual interdependence is highly important. Organisms don't just "make do" with their environments, whatever they find in terms of rocks, soil, water, light, temperature, precipitation, etc. Organisms also alter their environment to suit their needs.

The geographic distribution (or patterns) of species result from many factors. Changing one factor, e.g., the mean temperature, as is expected with global climate change, may not necessarily lead to a radical alteration of these patterns. How sensitive a species is to changes in single factors again depends on a variety of factors. Patterns are controlled by more factors than just climate. Similarly, production is the result of complex interactions and factors. Temperature and water availability, two climate-related factors, may be crucial for a certain species and in other cases may not be a so-called limiting factor. Because we do not yet know exactly how the global climate will change in the future, or how different species will respond to these environmental changes, predictions of production levels of any species are fraught with difficulties and uncertainties.

It is generally easier to look at the relationship between a species and just one or two environmental factors than to take all or even just a few relevant factors into account (e.g., soil conditions, other species competing for the same environmental resources, mobility, adaptability of a species). You will have the opportunity in some of the activities of this module to observe how patterns and production levels change over time as you change just one or two environmental factors, even though things are more complex in reality.

Before we can simulate species behavior in a computer model, we need some data to base our calculations on. Where do these data come from? Data are the result of observations. Our way of knowing about species or resources and how they interact with each other and the environment begins with observation. Observations are simply what our senses tell us about our surroundings (Gersmehl and Brown 1992). Ways in which we observe in this broad sense include thermal sensing (the sunshine on my shoulders feels warm); tactual sensing (touching) of a weed, e.g., velvet leaf (Abutilon theophrasti), telling us that the leaf is soft; visual sensing (and interpreting) that the leaf looks smooth. Other senses include hearing and tasting.

As we sense, we compare objects with each other as a way of recognizing and organizing information. A common tool for organizing information is classifying the observed objects into groups with similar characteristics. Classification into groups is a mental construct. These classes do not exist as such in nature; their purpose is to simplify our analysis by organizing information. These groups or units are found here and there, but not somewhere else. An observation that a unit once was there but is no longer is a fundamental observation of space and time. We develop ways of organizing "where" and "when" by using spatial coordinate systems and time scales, both of which must have communicated reference bases if they are to be used to transfer information.

Observation, in order to be informative, must:

As a matter of convenience, we commonly use artificial constructs to simplify the way we look at organisms. The concept of a species (a group of similar organisms that can produce viable offspring, and a term that classifies individual organisms in a simplifying manner) is basic to most of the biology of whole organisms. We must recognize that this is a mental construct, created by humans. All classifications have advantages (see above), but they also have the disadvantage of filtering information and thereby modifying and limiting what we learn from the original observations. For example, the construct of species classification may distill information from observations, but it may also obscure our view of the relationships between species or of evolutionary processes at work.

When we look at populations of organisms and mixings (the cause of diversity), we focus on the level or scale of individual members of that population and the processes occurring among them. Alternatively, when we try to understand organism production processes, we work at the molecular level. Occasionally, we view biological processes at scales different from the ones where they really occur. As a result, we may find inconsistent observations at different scales, or we may make claims about linkages between organisms and their environments that are not entirely appropriate. For example, we may see a correspondence (correlation) between a population or the range limits of certain organisms and various environmental traits. These correspondences are not necessarily causal. In other words, the distribution of an organism need not depend on features of the space in which it exists.

An example of this is the range of certain birch and pine trees. From observation we learn that certain birch and pine species are common in bogs and on the edges of swamps and wetlands. We conclude from this obvious correlation that the natural range of these tree species is delimited by the extent of bogs and wetlands, when in fact their range is theoretically much broader, i.e., they could exist in other types of environments as well, but because of competition from other tree species that fare better in non-swamp environments, the effective range of these birch and pine species is limited to areas where they have a competitive advantage, i.e., in bogs and on the edges of wetlands.

In order to avoid this mismatch between the scale at which we observe something and the scale at which the process of interest really happens, we will use theories here that work at the process level, and we will choose organisms from a larger population of organisms (a process called sampling) in a way that will recognize the factors at work at a particular scale. To do so we use a sampling design that defines the spatial and temporal distance between taking samples. Sampling designs that dictate either too wide or too narrow a spacing of observations are not useful for describing a pattern, nor are they capable of detecting a change in pattern. Transect A in Figure 1 below shows observations at 100-kilometer intervals across the forest (F) and prairie (P) border. If observation 6 were at the western edge of the forest, and the next observation point were 100 kilometers to the west into the prairie or to the east into the forest, we would gain absolutely no information about how the edge of a forest gradually changes to open land (prairie) or to forest proper. This distance would, however, be sufficient to determine where about the prairie-forest line was located (see transect A below). In transect B, the distance between observations is 200 kilometers. Water (W) is located between some observation points, but it is missed because the spatial resolution of the sampling design is not fine enough to capture this land cover feature.


Figure 1: Transects across the forest/prairie border at different observation intervals

The following units examine the issues of biological production, geographic pattern, and organism diversity in more detail. These features of the biosphere are related and must in the end be seen together because pattern and diversity affect production and vice versa.