Lizards on the Edge: Teachers Investigate Predation Risk

Field Notes From the Amazon

Field Report: 2023 Lizard Predation Risk in Amazon Forest Canopies


Date: July 12 – 19, 2023
Location: Explorama’s Napo-Sucusari Biological Reserve, Loreto Peru
Study Site: The Amazon Conservatory for Tropical Studies (ACTS) Canopy Walkway. Forest floor trail and canopy walkway.
Lead Researcher: Dr. Lindsey Swierk
Team Members: Dawn Porta, Kathy Hockman, Terry Wilson, Marissa Copan


Introduction
Tropical forests are three-dimensional spaces, with each level of the canopy experiencing different challenges and opportunities for the animals that live within them. To relatively small animals, like lizards, the gradient from forest floor to canopy represents an enormous shift in habitat type, including changes that are both abiotic (lighting, temperature, availability of shelter) and biotic (food availability, species interactions). In this research stream, we explored the behavioral ecology of lizards along this floor-to-canopy gradient. In particular, we examined if and how lizards’ risk of predation changes from the forest floor to the canopy, and how lizards may need to adapt to varying levels of predation risk.

We examined three different aspects of how the environment affects lizard predation risk from the forest floor to the canopy, specifically:
1) How does predation risk change for lizards from the forest floor to canopy gradient?
2) How does canopy openness affect the risk of predation?
3) Are larger lizards more likely to attract predators than smaller lizards?

The behavior of animals in forest canopies is very poorly documented by Western science in general, and many fundamental questions about how animals respond to environmental changes over vertical space remain largely unexamined. Lizards are an excellent model taxon for this exploration, as they are widely studied to better understand the processes of local adaptation and evolution to changing environmental conditions.

Methods

We created clay models from two sizes of plastic toy lizards (large = 8 cm and small = 4 cm, from nose to base of tail) wrapped with a single line of floral wire around the abdomen and then fully submerged in melted, gray plasticine clay.

Image 1: Dipping plastic lizards in clay at the ACTS field station

After hanging from their floral wires on a wooden pole to dry overnight, these clay-dipped model lizards were placed along a forest floor to canopy gradient along the ACTS canopy walkway.

Image 2: Lizards dry and ready to be placed along the trail and canopy walkway
Image 3: Placing lizard models along the ACTS canopy walkway

Model lizard locations were selected based on similar locations used by lizards in these habitats, which included tree branches, walkway platforms, beams, cables, and tree trunks and the forest floor at the base of the walkway. Each model lizard was tied to its perch using the floral wire, and was individually numbered and flagged near its location for easy identification and visibility. The level of canopy openness was defined by the amount of tree cover to open sky above at the placement location of each model. They were categorized as open (less than 25% tree cover), mostly open (25-49% tree cover), mostly closed (50-74% tree cover), and closed (75-100% covered) to allow us to estimate visibility of the models to aerial predators. For six days, model lizards were monitored each afternoon for possible predator marks. When an attack was noted, we recorded the body region that was attacked and took a photograph of the model lizard to permit a blinded reference for later review. The clay on the model lizard was then smoothed to restore its original form, and the model was returned to its original site. After field data collection was completed, the blinded photographs were reviewed, and whether a mark qualified as an attack (versus, for example, insect activity) was decided by consensus among all researchers.

Image 4: Lizard model without bite marks
Image 5: Lizard model with bite marks

Results

In total, 147 model lizards were placed along the forest floor to canopy gradient. Each model was checked daily for 6 days, resulting in 882 individual model-checking events. Of these individual model-checking events, 55 model-checking events (6.2%) were categorized as disturbed and 24 model-checking events (2.72%) qualified as predation events. Of all individual models, 37.41% were disturbed and 16.3% were classified as attacked by predators. By location, the most predator activity was noted on Platforms 3 (26.5 m) and 10 (27.1 m), with a 100% attack rate of models placed at these sites.

There was no difference in height above the ground of the models that were attacked versus those that were not attacked (Figure 1). However, we noted a potential relationship of canopy openness and attack rate; specifically, greater canopy openness correlated with a greater attack rate (Figure 2). Model lizard morphology may have also affected attack rates: 21.9% of all large models were attacked, versus only 13.7% of all small models. Attacks varied based on body region of model lizards: 60% of attacks were on the body, 49% on the head, 36.36% on a limb, and 12.73% on the tail (some model lizards were attacked in multiple locations; Table 1). One model lizard (3.7%) was missing.

Figure 1: Height above the forest floor (± 1 standard error) of clay-dipped model lizards that were not attacked and attacked by predators along an elevational gradient of the ACTS Canopy Walkway.

Figure 2: Figure 2. The percent (%) of clay-dipped model lizards attacked by predators in each canopy openness category (closed, mostly closed, mostly open, and open) along an elevational gradient of the ACTS Canopy Walkway.

Table 1: Body region of clay-dipped model lizards attacked by predators

Location of Model AttackNumber of Attacks(Can be attacked in multiple places)
Head2749.09%
Body3360.00%
Tail712.73%
Limb2036.36%
Model Missing13.70%

Discussion

Due to inaccessibility, there are few studies of animals living exclusively in tropical forest canopies. Given the opportunity to quantify predation risk using the ACTS Canopy Walkway, we assessed the relative level of risk to prey animals at various canopy levels in the Amazon Basin. This study can shed light on ecological relationships in the canopy and also have notable teaching significance. Our data can be used as a baseline for future research on the antipredatory behavior of lizards in the Amazon canopies, and how habitats affect if a species is at risk of predation and its potential need for future conservation efforts.

To promote more involvement and interaction with this project, we initiated a Community Science opportunity in which visitors to the Canopy Walkway can help document model lizard predation by submitting photos of 12 clay models maintained at different levels along the Walkway via a QR code; this will give others an opportunity to interact with and be a part of research efforts to better understand the environmental pressures facing canopy-living reptiles. Visitors to the canopy walkway can upload photos and leave notes on their observations of any predatory activity. For future investigations, minor logistical changes to the process have been noted in an internal document for the next field research team to continue. Additional and complementary experimental trials are planned for summer 2024 to increase sample size and to better understand this understudied ecosystem.


For additional information or questions about this field report, please contact Dr. Lindsey Swierk (lindsey.swierk@actsperu.org), Director of Scientific Research for The Morpho Institute and Associate Director of Research for the Amazon Conservatory for Tropical Studies. 

Learn more about the Amazon Research Initiative for Educators (ARIE)

Download Syllabus


Supplemental Documentation:

Table 2: Number and location of models placed along with disturbance data

LocationModels PlacedModels DisturbedOne model did not have location logged so total is 54, instead of 55
forest floor20630.00%
Walkway Entrance-PT1800.00%
PT14125.00%
Walkway PT1-PT2400.00%
PT24250.00%
Walkway PT2-PT35360.00%
PT322100.00%
Walkway PT3-PT55480.00%
PT5300.00%
Walkway PT 5-PT6800.00%
PT69333.33%
Walkway PT6-PT76116.67%
PT7400.00%
Walkway PT7-PT82150.00%
PT8300.00%
Walkway PT8-PT95480.00%
PT93266.67%
Walkway PT9-PT104125.00%
PT1055100.00%
Walkway PT10-PT11200.00%
PT11300.00%
Walkway PT11-PT125240.00%
PT 123133.33%
Walkway PT12-PT134375.00%
PT136350.00%
Walkway PT13-PT143133.33%
PT146350.00%
Walkway PT14-PT1511654.55%
LocationModels PlacedModels DisturbedOne model did not have location logged so total is 54, instead of 55
forest floor20630.00%
Walkway Entrance-PT1800.00%
PT14125.00%
Walkway PT1-PT2400.00%
PT24250.00%
Walkway PT2-PT35360.00%
PT322100.00%
Walkway PT3-PT55480.00%
PT5300.00%
Walkway PT 5-PT6800.00%
PT69333.33%
Walkway PT6-PT76116.67%
PT7400.00%
Walkway PT7-PT82150.00%
PT8300.00%
Walkway PT8-PT95480.00%
PT93266.67%
Walkway PT9-PT104125.00%
PT1055100.00%
Walkway PT10-PT11200.00%
PT11300.00%
Walkway PT11-PT125240.00%
PT 123133.33%
Walkway PT12-PT134375.00%
PT136350.00%
Walkway PT13-PT143133.33%
PT146350.00%
Walkway PT14-PT1511654.55%

Image 6: Teacher research in the Amazon rainforest is awesome and fun!

Share this with your friends: