Exercises for Module 2:
Module 2 at:

Module 2: Introduction to Local Biomes

The Local Biome and Global Navigation

By Dr. James A. Danoff-Burg, Columbia University

Today we begin a two-day study of the factors that determine the structure and composition of the local biome. As you explore the influences of these factors, you will become more familiar with your local biome. In addition to this ecological content, you will become familiar with Global Positioning System (GPS) units and a valuable tool called eBiome. Created specifically by and for the SEE-U program, eBiome will be used to store data and to construct data inquiries using spatial information. You will use GPS units and eBiome almost daily through the course of the semester.

Local Factors

As you’ve probably noticed, there is great variation within any single biome. The same trees are not found on both sides of a hill. As a river runs through an area, it greatly influences the composition of the plants and animals that are present. The edges of forests tend to be structured much differently than areas deeper in the forest. This set of observations seems to disagree with the range information we tend to find in species identification books.

For example, a tree identification guide shows that sugar maple (Acer saccharum) is found throughout the entire northeastern US. In fact these trees do best in deep, rich, well-drained soils in lowland areas and are primarily found below 1,600-m elevation. The young trees or seedlings prefer shaded conditions. If these conditions are not present with the shaded area of the range, the tree will probably not be present as well.

Therefore the factors that provide the local structure of a biome are idiosyncratic and site specific, in contrast to the features that determine which biome generally will be present at any one location. Abiotic forces largely determine the local structure on widely varying geographic scales. Because, the geographic scales at which these local factors operate vary widely, you must always consider scaling when you study your biome.

Examples of terrestrial abiotic forces that structure the local biome include proximity to water bodies, regional variations in rainfall, proximity to cities, topography, and slope. These factors are arranged from those shared over a wider geographic range to those that vary according to a much smaller scale.

Occasionally, biotic forces can be just as strong as abiotic forces in structuring biomes locally. Typically the changes due to biotic forces are because of changes in the population size of a single species. This species is usually called a keystone species. Keystone species include sea otters in Californian Kelp forests. Scientists have noted that when the sea otters were strongly hunted for their pelts, the Kelp forests nearly disappeared due to effects that cascade to other tropic levels in the community. All of these effects can be traced back to the changes that came about as a consequence of the removal of the sea otter.



Knowing your exact location is essential for conducting ecological studies. Often the best and most informative studies are longitudinal or long-term ones—those that involve repeated measurements of the same variables over many years. During the SEE-U program, we will be participating in many longitudinal studies of our own. Most of these studies are possible because the researcher knows her way around with great precision or because the study site is well marked. However, if the study is to be revisited many years later by novel researchers how would they know where to work? How do we navigate about a biome if we do not already know it?

Several navigation tools are available, many of which you may have already mastered. Road maps, topographic maps, compasses, navigation using the stars, sextants, and other tools and skills have historically been an integral part of determining where you are when conducting ecological studies. All of these are useful and informative, but none can tell you your precise location with great confidence.

Global Positioning System (GPS) Units can accomplish this task in perpetuity without any supporting materials like maps, flagging tape, spray paint, marking flags, and compasses. A GPS unit can provide a precise geographic location to within centimeters and altitude to within a few meters, depending on the quality of the units and the signal signal strength they receive.

GPS units work by taking readings from a network of more than 30 satellites that are constantly circling the Earth. These readings can be later analyzed using a computer algorithm and the precise location is produced. Georeferenced data are those for which GPS units were used to determine the precise location of the study site. Because of the many benefits of this technique, georeferenced data is the future of ecology.



We will start to intensively use the eBiome data tool during the next module, but a brief introduction to its utility is appropriate here. eBiome uses 3 technologies: GPS, Geographic Information Systems (GIS), and a database program.

GPS is used to determine the precise location of the data, while GIS is a type of software that allows you to organize and access the data by their location and data type. The GIS software that we will use is a program called ArcView. Unfortunately, most GIS programs do not allow for easy input for most of our data types. To input the data that we will be collecting during the class, we will use a specially modified online version of the database program called FileMaker Pro.

The steps from collecting data to analyzing it within eBiome are as follows. In the field, you take a location reading with a GPS unit. You process the location information using a program (called Pathfinder) upon your return to the lab. Next, you input the georeferenced data into eBiome using an Internet Browser program that references the screens made with FileMaker Pro. Then the data is transferred to the ArcView component of eBiome. Once they have been linked up with the preexisting data, these data and all others that have been input can be searched and output for other analyses.

The benefits provided to you and subsequent students by eBiome are many and unique. You can revisit the same site that another researcher has studied with great precision through the same season and across years, even if you have never been there. You can easily and quickly search all previously collected data by a specific geographic area or by a specific data type. Additionally, eBiome will serve as a central repository for all data collected as part of the SEE-U program. Therefore, you can study other biomes in depth using the raw data that has been collected by students and researchers who are onsite at those other biomes.

The data that you will be collecting will be stored and used by researchers who will publish using it. In this way, you will be contributing to ecology, even as you learn it!


Additional Relevant Online Resources

The Otter Project - for more information on reintroducing the California Sea Otter into the wild and the political and ecological ramifications of that effort.

The US LTER Network, or Long Term Ecological Research, exploring longitudinal studies in many biomes across the United States.

An introduction to Geographic Information Systems technology, or GIS, from the United States Geological Survey.

The USGS home page.

ArcView's homepage, by ESRI (the Environmental Systems Research Institute, Inc.).

FileMaker Pro's homepage.


All Materials Copyright © 2000 by James Danoff-Burg
All Rights Reserved.