Dr. Christine Jurasinski LabLearner Staff Scientist
Interdependence. It’s a word that comes up when talking about virtually everything in today’s world, from climate change to the global economy. When students in the LabLearner Program hear it they are likely to think about ecosystems and the relationship between producers, consumers and detrivores (decomposers such as scavengers, and microbes), and between prey and predator. For 4th grade LabLearner students, interdependence is explored through their study of food chains and food webs in the Ecosystems and Adaptation CELL. 8th grade LabLearner students take this knowledge farther investigating the flow of energy and biomass within ecosystems in the Ecosystems CELL. In addition, both elementary and middle school LabLearner students focus on how competition between herbivores or predation of herbivores by carnivores could increase or decrease the production of producers. For example, the more herbivores killed by carnivores or omnivores, the fewer herbivores to consume producers and the more producer biomass that will result.
This concept of the effect of competition and predator/prey relationship on producers has long been thought to be the mechanism by which carnivores influenced the diversity and abundance of producers in ecosystems. Now, new research from wildlife biologists at Michigan Technological University has suggested that carnivores may have a more direct and important effect on producers and the diversity of producers within ecosystems.
Joseph Bump, Rolf Peterson and John Vucetich have been studying the relationship between two parts of the ecosystem at Isle Royale National Park in Michigan: moose (herbivores) and wolves (carnivores). Their most recent findings have produced what they describe as a somewhat surprising link between the prey/predator relationship and the producers in the ecosystem. Bump, Peterson and Vucetich studied a 50 year record of the moose/wolf relationship that included observing the location of over 3600 moose carcasses. In addition, they conducted a 3.5 year study that compared the plant growth, soil microbes and fungi, and nutrient deposition in plant leaves and soil from control sites and those containing carcasses of wolf killed moose. Control sites were those that did not have moose carcasses. What they found was that soil at the wolf killed moose sites had 100 to 600 percent more potassium, nitrogen and phosphorus than soil at the control sites. In addition, plants from the wolf killed moose sites possessed 25 to almost 50 percent more nitrogen than plants from control sites. Bacteria and fungi were also higher at the wolf killed moose sites than the control sites.
When they combined this data with the 50 year record of moose carcasses what they found were “hot spots” of forest fertility- places in which nutrient, microbe and plant life were enriched. In essence, the researchers say that the wolf/moose prey/predator relationship created a cycle in which the decomposition of moose carcasses increased the nutrient deposition of the soil, resulting in an increase in the amount of plant (producer) biomass and an increase in the nutrient composition of the plants. Moose, which are attracted to nitrogen rich plants, were then drawn to these nutrient rich locations, depositing feces and urine further increasing the nutrient deposition into the soil. In addition, the increase in moose frequency to these areas increased the likelihood of predation by wolves and ultimately the increase of even more moose carcasses.
While these findings may seem intuitive, they are shockingly new to the study of ecosystems, which up to this point, has not had evidence of such a direct relationship between predators and soil fertility. In addition, the finding also suggests that there may be a direct relationship between predator activity and producer (plant) diversity because changes in nutrient availability often promote competition between different tree seedlings. Thus, the diversity and location of producers within an ecosystem may be directly related to predator behavior – a relationship that once seemed as unrelated as oil and water. Now, it’s just another example of interdependence.
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