Why we keep getting it wrong when it comes to sustainable food systems and the reptile trade
Updated: Jul 20, 2021
During a recent session of the 31st Meeting of the CITES Animals Committee, Malaysia were denied permission to increase their export quotas for pythons and monitor lizards. The outcome was based largely on negative interventions from the European Union and the United States; Parties from the Temperate North that have relatively little experience with tropical reptiles. This disparity between north and south has been noted by many working in biopolitics.
In my view, the case presented by Malaysia to increase their export quotas was well-justified. Populations of pythons and monitor lizards are healthy, and monitoring and management systems are rigorous. One intervention by a delegate from Austria provides a clue as to why there is such a chasm of understanding on this issue. The comment was about the apex predator status of pythons and monitor lizards – species that, if warm-blooded, frequently exhibit long generation times, low population densities and low productivity.
The nuances of ecological pyramids
Anyone who has studied ecology will be familiar with ecological pyramids. What is less well known is that there are arguably two different kinds of pyramids; one for endotherms (warm-blooded animals) and one for ectotherms (cold-blooded animals). In endothermic pyramids, a 10% rule applies – only 10 % of the available energy is transferred from one trophic level to the next. The rest is lost as heat energy. But in ectothermic pyramids, a more prudent rule applies. This is because ectotherms are 90% more energy efficient compared to endotherms. Reptiles, and particularly those species that are efficient at exploiting solar energy, require only 10% of the food inputs of similar sized birds and mammals. Unfortunately, Ecology 101 classes typically offer a singular understanding, and indeed the subtle differences are often conflated or biased towards temperate ecosystems.
How does this play out in policy?
The case against reptiles in trade relies partly on the premise that these animals are apex predators and keystone species. The intervention from the Austrian delegate correctly assumed that the trophic positioning of pythons and monitor lizards in maintaining ecosystem structure and function is much like that of golden eagles, but incorrectly assumed that compromising the population integrity in any way jeopardizes the wellbeing of the species (as may be the case if golden eagles were to be harvested as a substitute for chicken). Reptiles are top predators, but they are also ectothermic organisms, and therefore belong in a different ecological pyramid to golden eagles.
A case study in point
Another classic apex predator of the Temperate North is the grey wolf. This species occupies the very tip of the trophic pyramid; a tiny population reliant on enormous resources. There are approximately 12,000 wolves in Europe and 18,000 in North America. This works out at approximately 1200 tons of apex mammalian predator for an area covering approximately 35 million km2.
Now let’s look at another well-known and similar sized predator, the American alligator. There are 1.5 million alligators in the state of Louisiana - 540,000 tons of apex predator occupying an area of 16,000 km2.
The carrying capacity for alligators in Louisiana’s wetlands is around 125 individuals/km2. The carrying capacity for wolves in Yellowstone National Park is around 0.02 individuals/km2. For arguments sake, if wolves were ectothermic and sunshine was a non-limiting factor, Europe and North America could theoretically support well over 1 billion apex predators.
Obviously there are many confounding factors that make drawing these parallels nonsensical, but nevertheless, the fundamental message remains true – in terms of ecological pyramids, there are big differences between warm-blooded predators living in temperate climates and cold-blooded predators living in tropical climates.
In hot tropical climates, pythons and monitor lizards are capable of similar productivity rates to warm-blooded mammals. They have the potential to grow fast (e.g., annual growth rate of 15000%), produce vast numbers of offspring (e.g., up to 50 eggs per year for 20 years or more) and live in high densities (e.g., up to 1400 individuals/km2). They thrive in tropical agricultural landscapes much like rabbits do in the European countryside, and they are equally resilient to high levels of harvest, and even sustained persecution.
It would be extraordinary for Malaysia to comment on the conservation status of European rabbits, let alone interfere in EU rabbit management strategies or export quotas. This makes sense, since the hardwiring of our ecological understandings and abilities are informed by our biogeographical experiences.
The importance of local perspective
It is right that science is the principal driver for decision making, but a sound understanding of broader context is also important. There is no substitute for first-hand experience when it comes to the complexity of ecology and crafting nature-based solutions. If policymakers want to comment constructively on the reptile trade they should first join the dots between ectothermy, ecological pyramids and the sustainable use of reptiles in tropical countries.