As I was making a salad for dinner last night with fresh greens from our small greenhouse (which made a surprisingly amazing bounce back following our late season cold snap), my six-year-old son started talking to me about science. Now, my son tends to be extreme in all things, sometimes this is a good thing, and at other times… not so much. This was one of the good times. He was discovering a love of science (again) and was absolutely bursting with the excitement of discovery. When I came home from work that day, I’d brought him one of my old textbooks, a book titled Plants and Society from a course I took at university more than a decade ago. I always loved that book because it does a great job of explaining scientific concepts using common language and makes connections to our everyday lives that keep people engaged. When my son said to me after reading a few pages of the book, and while bouncing up and down in front of the kitchen counter, “I love science! I’m SO excited! I want to learn everything. Dad, did you know that nearly all life on earth relies on plant photosynthesis?”, it made me excited too. I mean, he’s right, science IS cool! And life on earth DOES rely on plants. Let’s talk more about that within the context of Mayne Island.
So, my son has just learned that plants power life on earth by converting energy from the sun into sugars through the process of photosynthesis, but that’s just the beginning. Most of you will also know that while plants are turning the sun’s energy into sugars, they’re also changing carbon dioxide into oxygen (which is fairly important), but it doesn’t stop there. You see, each species of plant is unique in ways that are important to the specific animals, insects, fungi, etc. that need them to live. Some of the differences are easy to see, a fir tree is taller than an orchid for example. Other differences can’t be seen, like the chemical differences that make some plants good or bad to eat for different animals. We have more than 600 different types of plants growing wild on Mayne Island, and that adds up to a lot of unique and different connections between plants and other organisms.
The energy that flows from the sun through plants and into the food web follows many twisting paths, and each organism along the path is reliant upon others to pass along the energy. When we lose species from the food web, or when once-common species become rare, it creates gaps in the food web, and that can have a domino effect within the system. Right now, on Mayne Island, there are dramatic changes happening in our local food web. Large gaps have formed where once common plant species and the organisms that rely on them have become rare.
These gaps are caused by deer overpopulation, which is in turn a result of the most important gap of all, the loss of large predators that eat deer. Mayne Island is not alone in this. Large predators have been forced away from many areas, and as a result, large herbivores (often deer species) have greatly increased. However, the situation on Mayne Island is one of the most extreme examples for a couple of reasons. First and most important, we are an island. As deer populations increase and all the best food plants disappear, it’s much harder for the deer to seek better food further away. Likewise, because of our island nature, it’s very difficult for large predators to move back into our area where their food is abundant. Second, we have introduced another large herbivore, the exotic fallow deer, which is making the impact on local food webs even more extreme.
The changes in our environment resulting from the loss of large predators are becoming very obvious. While the loss of dozens of native wildflower species may only be visible to those who study plants, the complete loss of the forest understory in many places of the island is more apparent. As the deer run out of their favorite foods, they move onto less and less edible species, ultimately eating plants like sword fern, salal, and Oregon grape. When deer start eating those species, it’s because all their other foods are gone, along with the role those plants played within the food web. So, what’s for dinner next?
To learn more about the big and often unexpected changes we have caused within ecosystems in the Southern Gulf Islands in the past 50 years, check out this recording of a recent talk by UBC professor Dr. Peter Arcese.