Unit 4: Impacts of Environmental Change on Organisms: Horses
- Students will be able to describe how biodiversity increases with the evolution of new species and is decreased by extinction.
- Students will be able to evaluate evidence and propose ideas about why changing climatic conditions and an increase in grassland environments led to changes in horse morphology and diversity.
- Students will be able to recognize that scientific ideas are subject to change based on new evidence.
This unit directly supports multiple InTeGrate guiding principles and addresses grand challenges by helping students to recognize that Earth is a long-lived, dynamic system with multiple interacting spheres. Specifically, students will use authentic geoscience data to appreciate some of the Big Ideas of Earth Literacy, including that climate has varied over time (Big Idea #3.8), life on Earth depends on, and is shaped by, climate (Big Idea #3.6), and speciation and extinction have occurred throughout Earth's history (Big Idea #6.2). In addition, students gain a better understanding of the nature of geoscience and how scientific ideas can change over time as new evidence becomes available (Big Idea #1.7).
Context for Use
This unit is designed as the fourth unit in the Changing Biosphere Module, but it could be used on its own. The unit could be incorporated into any introductory geology, geography, biology, or integrated science class. If used as a stand-alone lesson, some background on speciation and extinction would be helpful. It can be used for a variety of class sizes and should take approximately 50 minutes for the introduction, case study, and reflective activity.
Description and Teaching Materials
Materials for this unit include a brief introductory PowerPoint, case study, reflective activity (found at end of case study), and study guide. Also provided is an additional section that can be used with longer class/lab periods. The case study is designed as a group in-class activity, but could be assigned individually. Alternatively, it could be assigned as homework, including the optional section on the history of modern Equus, and used as a jumping-off point for a discussion of native vs. non-native species and wild horse management issues.
Introduction: Diversity in the Horse Family through Time (5 min or more, depending on use of optional video)
Introduce the Equidae (horse family) and changes in relative diversity of taxa over time using the introductory slides:
- Introduction to Equidae (PPT) (PowerPoint 2007 (.pptx) 6.5MB Jan13 17)
- Introduction to Equidae (PDF) (Acrobat (PDF) 6.6MB Jan13 17)
The PowerPoint slides are designed to introduce the Equidae (horse family). Please see notes section on the PowerPoint for tips and guidelines.
For Slide 5, the instructor should explain that the horizontal lines represent time ranges of each genus or clade, and the black connecting lines show lineages, or descendant-offspring relationships, similar to family trees connecting someone to their parents, grandparents, etc. It may be helpful to tell students not to worry about the Latin names, just point out that they represent individual genera. If more background on understanding evolutionary trees is desired, the "Reading Trees" website under References and Resources below can be assigned prior to class.
Slide 7 contains a hyperlink to an optional video explaining natural selection. This is useful for courses that have not covered this topic. For 50-minute classes, this video could be assigned prior to class as a pre-class assignment. For slightly longer, 60-minute classes, the clip can be stopped at 6:12. In longer classes (~75-minutes or more), the entire video can be shown. Alternatively, for classes (biology, biogeography, paleontology, etc.) in which natural selection and evolution have been discussed in detail, the video could be omitted.
Slides 8–15 serve as a prompts for the activity, including discussion prompts where students will report out on their ideas before moving on.
Case Study: Climate, Biomes, and Equidae (45 min)
The main activity is a case study:
- Climate, Biomes, and Equidae Student Handout (Word) (Microsoft Word 2007 (.docx) 2.1MB Jan13 17)
- Climate, Biomes, and Equidae Student Handout (PDF) (Acrobat (PDF) 2MB Jan13 17)
- Grayscale Climate, Biomes, and Equidae Student Handout (Word) (Microsoft Word 2007 (.docx) 1.5MB Jan13 17)
- Grayscale Climate, Biomes, and Equidae Student Handout (PDF) (Acrobat (PDF) 1.5MB Jan13 17)
Distribute the Case Study: Climate, Biomes, and Equidae Student Handout and have students organize into groups of three to four. The handout includes questions to help point students to key patterns and discoveries. Students should be told that they will each need to turn in their own handout.
To encourage reflection at the end of the unit, the student handout concludes with the following prompt: How did the information about Equidae affect your personal understanding of how environmental changes can shape life on Earth? This gives students with an opportunity to reflect individually on what they did in groups and summarize some of the key points. The responses can also give the instructor information about any misconceptions or missed key points that may need to be addressed in another class period. The reflection can be done at the end of class if there is time, or assigned as homework, with the handout turned in the following class period.
A solution set for instructors is here:
The solution set includes answers for the handout above, as well as the optional, additional section below.
Additional Section: History of Modern Equus and Discussion of Wild Horses (optional, if time permits)
This file contains an additional, optional section (Part 5) that could be used either with longer class or lab periods or if the case study is done as homework.
- Handout with Optional Part 5 (Word) (Microsoft Word 2007 (.docx) 2.1MB Jan13 17)
- Handout with Optional Part 5 (PDF) (Acrobat (PDF) 2MB Jan13 17)
- Grayscale Handout with Optional Part 5 (Word) (Microsoft Word 2007 (.docx) 1.5MB Jan13 17)
- Grayscale Handout with Optional Part 5 (PDF) (Acrobat (PDF) 1.5MB Jan13 17)
Teaching Notes and Tips
You will want to have PowerPoint capability.
The lesson is designed for a 50-minute lecture period. Options for adapting this to longer class periods include showing the optional video linked in the PowerPoint during class and adding the additional section on the history of modern Equus and wild horses.
Biology, paleontology or other courses with longer class or laboratory periods could spend additional time on the horse phylogeny (Figure 1) and reading evolutionary trees (see the "Reading Trees" website under References and Resources below) and/or discussing changing anatomy (Figures 3 and 4). Physical geography or Earth science instructors may wish to focus additional time on past climate reconstruction and trends (Figure 2). Additionally, instructors may wish to point out the various types of interdisciplinary (biological, paleontological, climatic) data used in this activity.
Questions posed to the class within the activity (especially the report-out questions) are best used as think-pair-share opportunities. Give students a minute or two to answer the questions on their own, then another minute to discuss their answers with a partner, then ask students to share answers with the class. Give students a chance to provide multiple answers before covering the topic/answers.
Please see the notes on the PowerPoint slides and Solution Set for additional tips, guidelines, and answers. These provide guidance for instructors to help ensure students make the necessary connections between environmental changes and horse evolution.
Passing the handout around as you begin the introduction or during the video can save time because students can more quickly start working when they form groups.
Possible Exam Question:
Learning Outcomes #1 and 2. Construct an explanation for how changes in climate and biome type led to adaptation and diversification in Equidae.
A rubric for grading the question can be found here:
Assessments from student handouts:
Learning Outcome #1. The student handout has questions (#3 and 11) that ask students to describe changes in Equidae diversity over time due to evolution of new species and the ultimate loss of all but one genera due to extinction. If students can answer these questions, they have adequately met the first learning outcome.
Learning Outcome #2. The student handout has questions (# 5, 6, 9,10) that ask students to evaluate evidence based on background information, graphs, and scientific illustrations to form ideas about why changing climatic conditions and an increase in grassland environments led to changes in horse anatomy and diversity. If students can answer these questions, they have adequately met the second learning outcome.
Learning Outcome #3. The student handout has questions (#11 and 12) that ask students to compare and contrast earlier diagrams that portrayed Equidae evolution as a straight line with today's multi-branched family tree and a graph of body mass over time to recognize that scientific ideas are subject to change based on new evidence. If students can answer these questions, they have adequately met the third learning outcome.
Students can use the Study Guide for self-assessment.
References and Resources
- Damuth, J. and Janis, C.M. 2011. "On the relationship between hypsodonty and feeding ecology in ungulate mammals, and its utility in palaeoecology." Biological Reviews 86, 733-758.
- MacFadden, B.J. 2005. "Fossil horses: evidence for evolution." Science 307, 1728-1730.
- MacFadden, B.J. 1986. "Fossil horses from 'Eohippus' (Hyracotherium) to Equus: Scaling, Cope's Law, and the evolution of body size." Paleobiology 12, 355-369.
- Mihlbachler, M.C., Rivals, F., Solounias, N., Semprebon, G.M. 2011. "Dietary Change and Evolution of Horses in North America." Science 331, 1178-1181.
Additional Resources for Instructors and Students:
- The Evolution of the Horse Family – by Michelle Tribble
- Reading Trees – A quick online article about how to read evolutionary trees that could be assigned prior to the lesson.
- Evolution by the Grassroots – A short New York Times piece that itself contains several good references.
- Florida Museum of Natural History Fossil Horse Cybermuseum
- The Paleobiology Database