Invader vs. Predator: Invasive species benefit from control of apex predators

This post is a part of a special series, written by undergraduate students in the University of Rhode Island’s Spring 2018 “Biology and Society” course. This course, taught by Dr. Lindsay Green-Gavrielidis, explores the intersection of biology and society. As part of the course, students wrote blog posts translating scientific articles related to ecology and society for a public audience.

About the Author: Evan G.

I am currently in the process of earning my Bachelors of Science in Biology at the University of Rhode Island. I plan to go on to a M.D. program in hopes to practice Emergency Medicine. While at the University of Rhode Island I have been able to expand on my knowledge of ecology and sustainable conservation, which has always been a passion of mine. Outside of my studies I enjoy whatever outdoor experience you can throw at me.

Human impacts on predators

In the paper, “Predator control promotes invasive dominated ecological states” written by Arian D. Wallach and fellow researchers, the impact on predators as a result of human control is explained. In the past there have been 5 major extinction events and many scientists argue that we are currently in the 6th mass extinction. The planet has seen a large decline in many reptile, bird, fish, and mammal species through habitat loss, human resource extraction, pollution, global climate change, and invasive species. The common thought is that invasive species are introduced to new places and simply out compete the other species by using up the resource and space that are available to the organisms living there. This change in resource availability can have a lasting effect on the region. In research conducted by Peter M. Vitousek et al. (1997) and David S. Wilcove et al. (1998), there was evidence that these new foreign species were a leading cause of extinction. However, Wallach and her team believe that the loss of species is not directly linked to the introduction of these foreigners, but actually due to a loss of predators in affected areas.

Humans have long hunted large animals, some to the point of endangerment or extinction. For example, elephants have been hunted for their tusks and mammoths for their meat and fur. Humans also hunt for game and protection, such as with the wolf populations in North America after European settlers landed on the continent. There has been a massive decline in wolf populations which, according to Rolfe O. Peterson et al. (1998), has led to booming moose populations, because wolves are the number one predator of moose. This change to the top predator population has an effect on all of the other members of the food web. More moose leads to less plants, as that is their main source of food. There are domino effects when you remove an animal from a region because that place has found a balance with the organisms living there. Like a house of cards, if you remove one card from the bottom the rest fall down. This is the fear with foreign species, that the balance will be thrown out of whack. Wallach and her team believe the bigger threat lies with the loss of apex predators, the “top of the food chain”. She and her associates hypothesized that the reason invasive species have done so well in certain areas is because there has been a human effort to control the predator populations. With less large predators there is more room and food for smaller, foreign, predators to take over.

Changes in dingo populations in Australia

Wallach and her team conducted their research in Australia over a 3 year period where the main apex predator is the dingo, a member of the wolf family. In Australia there has been a concerted effort to control the dingo population for fear of attack. When the English colonists moved onto the continent hundreds of years ago they brought with them many new species, including herding animals like goats and cows, as well has mid-sized predators like cats. In their research, Wallach and her associates found that in areas where there was active control of dingos (meaning they were being poisoned by Australian officials) these smaller invasive predators had higher populations then those where there were more dingos. They also found that in areas that previously had control programs but then stopped the programs, the number of invasive species dropped and the areas started to shift back to their prior state. Their research not only supported their hypothesis, but it showed that even after new species had shown up and taken over, causing the numbers of the animals that once lived there to decline, once “order was restored” things began to revert back and more of the original species’ populations began to grow.

Future directions

This study opens new doors for research in how big predators help ecosystems maintain robustness to keep from foreign invaders to take over. The hope is that more research will be conducted pertaining to this topic, in hopes it will shed new light on how to move forward with conservation programs. If people understand the complexities of how these ecosystems operate and maintain balance then humans have a better shot at keeping them from falling apart due to human caused problems. The researchers hope that in the future instead of trying to replace the predators killed with man-made interventions, people help the “natural” defense systems that already exist in these ecosystems, which will help control invasive species and overall help stop extinctions from happening on such a grand scale.

Source Article

Wallach, Arian D., Johnson, Christopher N., Ritchie, Euan H., and O’Niell, Adam J. 2010. Predator control promotes invasive dominated ecological states. Ecology Letters 13: 1008-1018 https://doi.org/10.1111/j.1461-0248.2010.01492.x