Changing Planet: Disappearing Lizards


Students review the nature of ecosystems and food webs and investigate the role of global warming on the extinction of lizards


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Developed by NESTA/Windows to the Universe team members Missy Holzer, Jennifer Bergman, and Roberta Johnson

Grade level:


  • Food chain and food web games: 1 class period
  • Part I: 30 minutes
  • Part II and Part III: 60 minutes
  • Part IV: 45 minutes
  • Discussion: 30 minutes
  • Note that parts of this lesson may be assigned for homework
Student Learning Outcomes:
  • Students will identify interactions among abiotic and biotic features of a food web
  • Students will explore adaptive characteristics of lizards and the ecosystems in which they live
  • Students will interpret model data
  • Students apply extinction scenarios to their local ecosystems
Lesson format:

Research, model interpretation, discussion

Standards Addressed:

  • 5-8: Content Standard A: Science as Inquiry
  • 5-8: Content Standard C: Populations and Ecosystems
  • 5-8: Content Standard C: Diversity and Adaptations of Organisms
  • 5-8: Content Standard D: Structure of the Earth System, Earth History
  • 5-8: Content Standard F: Populations, Resources, and Environments
  • All levels: History and Nature of Science: Science as a Human Endeavor, Nature of Science, History of Science
  • All levels: Science and Technology Standard: Understanding about Science and Technology
  • All levels: Science in Personal and Social Perspective Standard
  • All levels: Assessment Standard B: The Ability to Communicate Effectively about Science


  1. For background information on how climate change is affecting lizard populations around the world, watch the movie Changing Planet: Disappearing Lizards. This movie is linked on the first slide of the PowerPoint presentation. Showing the Powerpoint presentation to your students along with sharing background information from below, will provide your students a foundation on reptiles that will be very helpful before exploring the rest of the lesson. Also explore these topics on the Windows to the Universe website at the links listed below.
  2. Gather materials and print out the student worksheet (one per student). Parts of this lesson may be omitted based on the prior knowledge and grade levels of the students.
  3. This Changing Planet program focuses on the challenges lizards face in overcoming the effects of a warming climate. Unfortunately neither survival option is viable for our global lizard population. Adaptation to warming temperatures via shifting their habitats will only cause new challenges since it would increase the competition for resources in the new location, thus leading to extinctions of the lizards previously living there and/or for the new arrivals. Evolutionary adaptation and the associated complications of adapting to warmer temperatures is not a viable option either. "Estimates of evolutionary rates required to keep pace with global change indicate that sustained and intense selection compromises population growth rates, precipitating extinctions." (Sinervo, et al, 2010). In this lesson, students are introduced to the characteristics of lizards that complicate their chances for survival as Earth's global temperature climbs. Students will identify lizards in peril of extinction and investigate the impacts of extinction on local food webs.
  4. To assess student understanding of the need for biodiversity, ask students to create a list of the organisms they would find in a local food web. Have students compare lists with a partner and then have each student create a drawing of the food chain utilizing animals from both lists. Depending on student background knowledge and knowledge of local flora and fauna, the chains may be quite simplistic, but members of each of the main trophic levels should be present (producers and consumers including herbivores and carnivores and omnivores, and decomposers). Ask students to share their drawings with the class, and then store their work until the end of the lesson. Note: Students in grades 5-9 will enjoy playing Food Chain Checkers to create a simple model of how a food chain works, and from that they will gain a better appreciation for the complicated nature of a food web in the next step.
  5. A key point that the scientist makes in this program is that with the loss of lizards from a local ecosystem, an entire food web faces collapse; if not immediately, then over a brief period of time if the organisms cannot adjust to loss of resources. This delicate balance is obvious to students when they play a food web game using simple materials. You will need yarn and signs with the following food web components: sun, turtle, snake, lizard, grasshopper, robin, toad, grass, berry brush, hawk, quail, dandelion, mouse, worm, rabbit, cow, flea, meadowlark, owl, wheat, tick, fox, weeds, coyote, mushrooms, worm, dragonfly, mosquito, microscopic bacteria. You may increase or decrease this list depending on the number of students playing the game. Ask students to sit in a circle, and give each student a sign. Pass the ball of yarn to one of the organisms. That person will hold onto the end and pass the ball of yarn to what it "eats", and then that organism will hold onto a piece of the yarn and pass the ball to what it eats. Play continues until the ball of yarn ends up at the sun, where the yarn is cut. Play begins again with a student who has not yet held the ball of yarn. Each time the ball of yarn is tossed to the sun, cut it and begin play another round. Continue to play until all of the organisms are holding onto the yarn and the center of the circle of students looks like a web with yarn criss-crossing throughout the middle. Ask students to make observations of their food web using the terminology developed in the previous step of this lesson. Pull on one of the strands of yarn, and ask the students who felt a tug. Next, ask the "sun" to pull on all the yarn ends they are holding, and ask the students who felt the tug. Now ask one of the organisms to drop their yarn, and ask the students what this represents and to describe the implications of the missing organism from the food web. Discuss the complexities of a food web based on their model, and also discuss the limitations of their model to accurately depict all the complexities of a food web. At this point, students should also bring into the discussion the roles of biotic and abiotic factors needed to support an ecosystem. For a detailed description of this activity visit River Venture Estuary Teacher Resources. The final step in this part of the lesson is to ask students to combine their food chains from the previous step in this lesson to create a drawing of a food web.
  6. Distribute student worksheet to each student. In Part I, students read the press release about the work of Dr. Sinervo and his colleagues and answer questions. In Part II, students define lizard and ecology terms germane to the topic and apply these definitions to understanding the issue of lizard extinctions. In Part III, students interpret model data showing the relationship between global warming and the extinction of lizards. Read the AAAS article ahead of time so you are prepared to assist students in their interpretations. In Part IV, students apply what they learned to the look into the deterioration of food webs and ecosystems and to explore the importance of biodiversity within an ecosystem. Locate websites for students to use to find information about species living in your state. The components of this lesson have been designed with flexibility so that a few sections may be assigned for homework, and may be completed by individual students or pairs of students. The links below may be given to students to facilitate their search for information about various lizard species.
  7. For wrap up discussion -- the prognosis for our planet's lizards is not good according to the work of Dr. Sinervo and his colleagues. Students may become upset over projected extinctions, and it would be a good time to remind them about everyone's role as stewards in sustaining our planet deep into the future. Brainstorm a viable list of solutions for sustaining the biodiversity in their local food webs.


Review student responses to all questions on the handout and assess the quality of the responses in the wrap-up discussion to ensure students understand the content of this lesson.


Always use safe laboratory practices


Store materials for future use.


  • Consider taking students outside to complete a local food web assessment. Decide on a protocol appropriate for the grade level and course being taught, and collect baseline data in which future students can compare their findings to the findings of previous years.
  • This lesson focused on the effects of a warming planet on global lizard populations. Select and manipulate other abiotic factors that may affect a local food web. For instance, sections of our country experience long periods of drought. What are the impacts of drought on a local ecosystem? What can be done (if anything) to lessen these impacts?
  • Conservation International identifies key hotspots around the globe (the richest and most threatened reservoirs of plant and animal life on Earth). Assign student groups to investigate different hotspots to identify the changing biotic and abiotic factors that make these places hotspots for (threatened) biodiversity.


This text is meant as a supplement to the the PowerPoint presentation which has many images to illustrate the following points.

Reptiles are some of the most misunderstood creatures. In fact, snakes are reported to be the most feared of any animal on Earth. Reptiles have had a consistently bad rap for a long time - from the serpent in the Garden of Eden to the basilisk of Lord Voldemort. Reptiles are seen as sinister, scaly, deceitful and more than a bit threatening. But they are an integral part of the ecosystem in which they live, and are found on every continent except Antarctica.

Reptiles are a diverse set of creatures. They include lizards, snakes, crocodilians, turtles, Amphisbaenia (worm lizards) and even the tuatara, which is one of the oldest living vertebrates on Earth (this reptile looks like a medium-sized lizard, has a lifespan of 80-100 years and belongs to its own order due to anatomical differences).

Reptiles can be found in the African savannah (ex: black mamba) to the rainforests of the Amazon (ex: green anaconda), urban areas (ex: geckos) to the coral reefs of the ocean (ex: sea turtles). Some can jump, bear live young, burrow, swim, climb, or even fly! Ok, the flying might be a bit more like gliding when it comes to "flying" snakes, but you get the idea - reptiles are a diverse and very interesting group!

Here are some interesting facts to pique your interest further.

  • The largest living reptile is the saltwater crocodile that weighs in at 2,000 kg (4,400 lb) and was measured at 7 m (23 ft) (according to the Guinness Book of World Records). That's one big crocodile!
  • The most massive snake is the green anaconda of South America with the largest on record being 5.21 m (18 ft) and 250 kg (550 lb).
  • The reticulated python of Asia can be over 10 feet longer, but is usually much lighter than the anaconda.
  • The most venomous snakes in the world are actually found in the ocean (Belcher's Sea Snake) and a few milligrams of its venom would be enough to kill 1,000 people. Luckily, humans rarely encounter them and even when they are pulled into a fisherman's net in South East Asia, they are fairly docile.
  • The Inland Taipan is the most venomous land snake, but again, this snake is not particularly aggressive and is not encountered often in the wild. Its bite could kill about 100 humans, or 250,000 mice!
  • There are some places in the world outside the poles, where snakes are not found - e.g., Ireland and New Zealand! I guess these islands are just too far to swim to!
  • Meanwhile, people are trying to control invasive species like Burmese Pythons that have proliferated in the Everglades, with over 300 being removed each year since 2008.
  • The Green Anole lizard has recently become the first reptile to have its complete genome sequenced.
  • Finally, snakes have some unlikely predators, and its worth keeping in mind that hedgehogs, mongooses, peacocks, and even some insects like aquatic beetles and praying mantises have been known to snack on a snake or or its eggs at times.

Reptiles are vertebrates, that is, they have backbones. Some lay eggs and some bear live young. Some reptiles rear their young for a time. It makes the species seem a lot less intimidating to imagine a mother rattlesnake with her five tiny babies basking in the sun near their den - and that is just what some mother snakes do! Reptiles do not undergo a metamorphosis like amphibians do, i.e., baby snakes look like their parents, only smaller.

Many people do get reptiles and amphibians confused, after all lizards do look a bit like salamanders. Others think amphibians live strictly in water environments while reptiles live in dry desert environments. While amphibians do share the fact that they are ectothermic ("cold-blooded") vertebrates with reptiles, they hatch into a larval phase with gills, and undergo metamorphosis to an adult phase with air-breathing lungs. Amphibians include newts and salamanders, frogs and toads, and caecilians. While some reptiles live in the desert, there are quite a few like alligators, crocodiles, turtles, sea snakes, and marine iguanas that much prefer an aquatic environment. All reptiles breathe using lungs.

Reptiles are "cold-blooded". This is a layman's term meaning that reptiles do not use metabolism to maintain their body temperature. Scientists refer to these creatures as ectothermic. They control their body's temperature using external means like basking in the sun or lying on a dark surface to get warmer, or seeking shade or water to cool down. Climate change is affecting many reptiles because rising temperatures mean these animals must retreat to shade to find their perfect body temperatures. If reptiles have to spend more time in the shade, they have less time to forage for food and find a mate for reproduction. The scientist in this Changing Planet episode, Dr. Barry Sinervo, mentions that global lizard populations are dying at such a fast rate, and that one of his biggest fears is that the lizards do not have enough time to adapt to the changes in climate. If lizards disappear from an ecosystem, this obviously affects all of the predators (like other reptiles or birds or mammals) that feed on them and it affects the prey the lizards would catch like insects or rodents. Climate change is affecting a vital link in our ecosystems.

There is a lot of specific information available about the lizards of California. Dr. Sinervo studies alligator lizards quite often because the loss of these lizards can truly impact entire ecosystems, especially up and down the food chain. Alligator lizards can be up to a foot long and are quite good to study because they are found in the Americas, Europe, Asia, and Africa. Its long body and powerful jaws probably gave the lizard its common name. They are active during the day, inactive during cold weather and nocturnal if it gets really hot for a period of time. They eat small invertebrates, other lizards, small mammals and occasionally a small bird or its eggs. They are egg-laying and live in grassland and open forests and can often be found hiding under rocks, logs, boards or trash. Their color is brown, grey or yellowish. If you've read through this paragraph, you may think that alligator lizards sound quite common. And, in fact, you'd be correct - they are a model organism to study because they will teach us so much about other lizards, other reptiles and other species. And when a model organism is found missing in certain parts of the world (like Mexico where reproduction of alligator lizards has shut down due to rising heat), there is cause for concern! And, of course, each organism, however common it might seem, is worthy of being protected, because upon looking in more depth, each organism is unique and vital to its ecosystem. Did you know that alligator lizards actually have scales that create a fold along each side? The folds can be used to hold food, eggs, or live young. Alligator lizards can also deliberately detach its tail as a defense tactic (the writhing tail distracts a predator while the lizard scurries away) and then can regenerate its tail in a short time. Beats my physical activities for the day!

Remember some basic reptile safety - it is best to leave any wild animal alone if you happen to stumble across it. Many reptiles are very docile and are not looking to harm humans (or their pets), but if they feel threatened, they can make loud noises, bite, musk, pee or poop to defend themselves. It's best to leave handling of reptiles to the experts and touch and experience these beautiful creatures in the safe environments of zoos, wildlife preserves or nature centers. The study of reptiles and amphibians called herpetology is a fascinating field of study and there is certainly a lot to learn about these unique creatures - even if they do have a bit of a scaly "wrap"!



Last modified September 7, 2011 by Jennifer Bergman.

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