About This Project

Ask the Scientists

What is the context of this research?

A non-native species is a species that forms a self-perpetuating population in a region where it has not historically been found. This is very similar to an invasive species, the only difference being that invasive species cause some form of economic, environmental, or ecological harm after introduction. It is important to remember that any non-native species has the potential to become invasive depending on the circumstances.

Many factors determine if a non-native species will establish populations where they have been introduced, including interactions with native organisms. For example, a non-native species is more likely to establish if it can avoid being eaten by predators in their new range. One way organisms can reduce their chances of being eaten is though inducible defenses, which are physical or behavioral changes in an organism triggered by the presence of a predator or other risk cues. If a native predator triggers inducible defenses in a non-native species, that species should be more likely to survive, reproduce, and spread.

Despite the potential role inducible defenses may play in the successful
establishment and spread of non-native species into new areas, few studies have addressed this issue (Kimbro et al. 2009, Grason and Miner 2012). My previous work has shown that the non-native purple varnish clam, Nuttallia obscurata, will increase its burrowing depth (an inducible defense observed in other burrowing clams) in the presence of the Dungeness crab, Metacarcinus magister, a predator native to the Pacific Northwest (PNW). However, it is unkown if this response played a role in the initial establishment of the varnish clam in the Pacific Northwest.

Having found that Dungeness crabs trigger an inducible defense in the purple varnish clam, there remain two major questions that need to be answered:

1. Are the clams responding to chemical (smell) or physical (touch) cues from Dungeness crabs? A response to chemical cues suggests the clam's reaction is specifically triggered by Dungeness crabs, while a response to physical cues suggests it is a general response to being touched and predator identity does not influence the clam's reaction.
2. Do clams from populations naïve to the Dungeness crab (those from their native range in Japan) respond in the same way as clams from populations that have coexisted with Dungeness crabs for years (those from their introduced range in Oregon and British Columbia)? If varnish clams from Japan do not burrow deeper in the presence of a Dungeness crab, this suggests that varnish clams in Oregon have learned over time to perceive the crab as a threat and that inducible defenses probably did not play a role in their successful establishment in the Pacific Northwest.

What is the significance of this project?

To the best of my knowledge, this is the first study to examine how completely naïve populations of an established non-native species respond to cues from predators they encounter in their introduced range. By using completely naïve specimens, this study will provide insight into species interactions that occur when species are first introduced into new regions.

Other goals of this project, particularly determining which type of predator cues trigger inducible defenses, have been addressed by other researchers for other species. What makes my research unique in this regard is that they have never been examined for the purple varnish clam. Prior to this study there was no evidence that varnish clams possess inducible defenses, a phenomenon for which we now have documented proof. Through this project we will learn more about the behavior of this species and differences in behavior across geographic regions. If geographic origin significantly alters how the purple varnish clam responds to cues from a potential predator, then the source of clams may need to be taken into account when managing future introductions of the purple varnish clam.

What are the goals of the project?

1. Determine what cues (physical or chemical) from the Dungeness crab cause varnish clams in Oregon to increase their burrowing depth.
2. Determine if the response (burrowing depth) of varnish clams to the presence of a Dungeness crab is different among specimens from populations in Oregon (non-native), British Columbia (non-native), and Japan (native).
3. Use the results from the aforementioned work and my previous research to write a paper that will be submitted for publication in a peer-reviewed scientific journal..
4. The research will be used to form the basis of a chapter in my dissertation.
5. Provide opportunities for undergraduates at Portland State University and the Portland Metro Area to gain experience doing research in the field and in the lab.