What are the ecological consequences of trophic downgrading in mixed/short grass prairies in North America?

Dennis Ruez, University of Illinois at Springfield
Megan Styles, University of Illinois at Springfield
Felisa Smith, University of New Mexico
Eric Grimm, Illinois State Museum
Author Profile

Summary

North American ecosystems have fundamentally changed over the late Pleistocene and Holocene; from a system dominated by mammoths, to bison, to domestic livestock. Given the very different body size and herd formation of these 'ecosystem engineers', it is likely that animals influence soil structure, water tables, vegetation and other animals in the ecosystems. What has been the ecological influence of the continued 'downsizing' of the largest animals in the ecosystem?

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Learning Goals

  1. Students will understand
    • that ecosystems are dynamic and change is continual.
    • significant patterns in and impacts of climate change during the late Pleistocene and Holocene in North America.
    • how climate change, human action, and alterations in species distribution have collectively influenced the distribution and abundance of grassland ecosystems in North America.
  2. Students will be able to use the Neotoma database to create a map of the distribution of fossil remains of species.
  3. Students will investigate the role that "ecosystem engineers" play in driving ecosystem change. In particular, they will evaluate the ecological consequences of trophic downgrading of top herbivores (mammoth to bison to domestic livestock) during the late Quaternary.
  4. Students will develop hypotheses about the role played by top consumers in shaping observed variations over time in grassland ecosystems.

Context for Use

This activity is intended for undergraduates and can be done over several class periods. Before beginning, students need to be familiar with the concepts of ecosystem engineers, trophic downgrading, and at least a general sense of late Quaternary climate shifts.

Instructors could follow this introductory activity with a deeper exploration of interactions between different species by computing the area of the geographic range and overlap within and between species over time; for example, see this teaching activity:
Advanced exploration of the ecological consequences of trophic downgrading in mixed/short grass prairies in North America.

Alternatively, one could follow up with lecture about or discussion of one or more of the following: the terminal Pleistocene megafauna extinction, re-wilding and its role in modern conservation biology, the ecological differences between short and tall grass prairies, how human modifications of landscapes have influenced the extent of grasslands in the US, or other related topics.

Description and Teaching Materials

In part 1 of this activity, students will explore the Neotoma database using data on mammoths and mastodons. Students will generate maps that allow them to describe some basic patterns in the ways that geographic distribution of mastodons and mammoths changed over time. They also will investigate possible relationships between these and other species and proposed hypotheses about the causes of observed patterns and changes in distribution over time.

In part 2, students will explore one method for quantifying changes in the distribution of Mammuthus sp. (mammoths), Mammut (mastodons) and plants typical of short/mixed grass prairies (Artemisa), tall grass prairies (Ambrosia) and Picea sp. (spruce). Specifically, they will calculate the change in geographic range for each species over time (in kilometers, based on the centroid – the midpoint of each range, calculated using the mean latitude and longitude for the samples).

Download the student handout in PDF or Word format:

Teaching Notes and Tips

Because there are multiple reasonable ways to draw the geographic range of taxa in the ArcGIS component, instructors should expect there to be variation within results.

If you would like to have your students be familiar with the Neotoma database before beginning this exercise, you could have them complete the Exploring the Neotoma Paleoecology Database exercise first.


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