Do not adjust your monitor

By James Hehre

Wikipedia Commons

Wikipedia Commons

Wikipedia, the ultimate repository for knowledge in the new millennium, has this to say about the water monitor lizard:

“The Water monitor, (Varanus salvator) is a large species of monitor lizard capable of growing to 3.21 metres (10.5 ft) in length, with the average size of most adults at 1.5 metres (4 ft 11 in) long. Maximum weight of Varanus salvator can be over 25 kilograms (55 lb), but most are half that size. Their body is muscular with a long, powerful, laterally compressed tail. Water monitors are one of the most common monitor lizards found throughout Asia, and range from Sri Lanka, India, Indochina, the Malay Peninsula and various islands of Indonesia, living in areas close to water… Water Monitors are carnivores, and have a wide range of foods. They are known to eat fish, frogs, rodents, birds, crabs, and snakes. In the Philippines they are known as chicken lizards because of their predilection for eating domestic fowl.”

I didn’t know any of this as I lay tucked in my mosquito net on the porch of the fieldhouse where I sleep. It was dawn. I felt a tickling on my feet and awoke to a four-foot lizard tickling my mosquito repellent covered feet with its long, snake-like tongue. I’m not sure the exact thought that flashed through my still groggy brain. I think it was something like, ”Wow. That is a really big lizard. I wonder if it bites.”

This particular lizard seemed unconcerned with me, brushing past and striding purposefully (well at least as purposefully as a lizard can appear) into the fieldhouse. The situation was resolved easily enough. I roused myself and walked around the house to the kitchen area, where, taking up the housekeeper’s broom, I confronted my guest and invited him out the door. He didn’t take much convincing. Water monitors are considered tasty by many in the Philippines and he seemed to be taking no chances, choosing to leave the way he came, probably content to feast on the local chickens which coincidentally had been disappearing lately.

James Hehre/Project Seahorse

James Hehre/Project Seahorse

The monitor lizard was by no means the first animal I’ve encountered during my stay at the field house, and actually our bamboo-and-thatch base of operations also serves as home to all kinds of plants and animals, from fungus and algae to termites, centipedes, spiders, land crabs, and a host of lizards, toads, mice, shrews, bats, birds, one really big snake, and at least one really huge rat like the one that got stuck in my research assistant Gerry’s mosquito net several nights ago. I awoke to the spectacle of the two of them doing racetrack laps around the inside of the net, with Gerry occasionally lifting an edge in an attempt to let himself or the rat out, though at the time it wasn’t entirely clear which. Now was it clear who was more traumatized by the event, Gerry or his guest. Stifling my laughter, I eventually set them both free. (As Charles Shultz says, humour is when the rock falls on someone else’s head.)

The fieldhouse contains an interesting and diverse ecosystem. At its most basic definition, an ecosystem is simply all of the organisms in an area and the non-living things they interact with like sunlight, water, and soil. An ecosystem can be contained within a small puddle with only a few components or it can be as large and complicated and contain thousands of components like the coral reefs in my own study. Of course the fieldhouse could be considered an artificial ecosystem, one that doesn’t occur normally in nature because it’s based around a man-made structure.

As an ecologist I think it would be really interesting to compare the number and kinds of different animals that live in the house to the animals that lived on this particular patch of land before the house was built. It might be reasonable to expect the number to be less, since trees and shrubs that naturally provide habitat had to be removed to build the house.

But it’s also possible that building the house may have actually created more available food and shelter, so it may contain more animals than before.  The answer may lie in the condition of the land before the house was built. A fieldhouse built on a pristine tract of jungle might displace more animals than a fieldhouse built on land that had already been cleared for agriculture. (It would actually be a bit more complicated that, and would also depend on other things like the size and type of house and maybe how many other houses were nearby.)

It’s an interesting question, and not unlike the research that I’m conducting on seaweed farms on shallow coral habitat. Seaweed farms placed on pristine coral will probably have a deleterious effect because of trampling, shading, and because people remove the coral to keep it from cutting the lines which hold the seaweed in place.

But in the Danajon Bank, where I am working, there is very little pristine coral remaining. Most of it has been subjected to decades of dynamite and cyanide fishing, kai kai (which is breaking the coral apart with an iron bar to get at the fish and other animals hiding inside), and coral mining for roads, piers, and fish farms. So I’m curious whether putting a seaweed farm in an area that has already been disturbed may actually create new sources of food and shelter for the fish and other animals that live on the reef.

I guess in that light, the water monitor who came into the house (probably looking to turn Gerry’s midnight guest, the rat, into dinner) was only performing his role as the top predator in our fieldhouse ecosystem. Next time I suppose I will leave him alone to do his job.

James Hehre is a PhD student with Project Seahorse.