Emily Grason

Publications (3) View all

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  Available from: Emily Grason

  Article: Preference alters consumptive effects of predators: top-down effects of a native crab on a system of native and introduced prey.

  Emily W Grason, Benjamin G Miner
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  ABSTRACT: Top-down effects of predators in systems depend on the rate at which predators consume prey, and on predator preferences among available prey. In invaded communities, these parameters might be difficult to predict because ecological relationships are typically evolutionarily novel. We examined feeding rates and preferences of a crab native to the Pacific Northwest, Cancer productus, among four prey items: two invasive species of oyster drill (the marine whelks Urosalpinx cinerea and Ocenebra inornata) and two species of oyster (Crassostrea gigas and Ostrea lurida) that are also consumed by U. cinerea and O. inornata. This system is also characterized by intraguild predation because crabs are predators of drills and compete with them for prey (oysters). When only the oysters were offered, crabs did not express a preference and consumed approximately 9 juvenile oysters crab(-1) day(-1). We then tested whether crabs preferred adult drills of either U. cinerea or O. inornata, or juvenile oysters (C. gigas). While crabs consumed drills and oysters at approximately the same rate when only one type of prey was offered, they expressed a strong preference for juvenile oysters over drills when they were allowed to choose among the three prey items. This preference for oysters might negate the positive indirect effects that crabs have on oysters by crabs consuming drills (trophic cascade) because crabs have a large negative direct effect on oysters when crabs, oysters, and drills co-occur.
  PLoS ONE 01/2012; 7(12):e51322. · 4.09 Impact Factor
• Article: Behavioral plasticity in an invaded system: non-native whelks recognize risk from native crabs.

  Emily W Grason, Benjamin G Miner
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  ABSTRACT: Inducible defenses have the potential to affect both invasion success and the structure of invaded communities. However, little is known about the cues used for risk-recognition that influence the expression of inducible defenses in invasive prey, because they involve a novel threat. In laboratory experiments, we investigated behavioral defenses induced by a native crab on two invasive oyster drills (marine whelks Urosalpinx cinerea and Ocinebrina inornata). Both drills hid more often and reduced their feeding rates when they detected predators consuming conspecific prey. Examination of the responses of U. cinerea to specific cue sources (predator kairomones, conspecific alarm cues) indicated that this species had the strongest responses to cues from injured conspecifics, but that it did recognize the novel crab predator. Our observation of native predator (per se) recognition by an invasive marine prey is novel. In addition, we observed that neither species of drill reduced their defensive behavior to reflect predation risk shared by a group of prey. The lack of density dependence in risk-assessment could cause populations of invasive prey to transmit both quantitatively and qualitatively different community effects over the course of an invasion as abundance changes. Together, these findings demonstrate several ways that the risk-assessment strategies could be important in establishment and post-establishment dynamics of invasive prey.
  Oecologia 11/2011; 169(1):105-15. · 3.41 Impact Factor
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  Available from: com.univ-mrs.fr

  Article: Invasive species as a new food source: does a nudibranch predator prefer eating an invasive bryozoan?

  Marney C. Pratt, Emily W. Grason
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  ABSTRACT: Membranipora membranacea is an invasive bryozoan that was first found in the Gulf of Maine in 1987 and within two years became the dominant organism living on kelps. Membranipora may have become dominant so quickly because it had little competition in a relatively unoccupied niche; however, lack of predation has also probably played a major role. Where Membranipora is native, there is usually a specialist nudibranch predator that keeps the population in check. For example, in European populations, the nudibranch Polycera quadrilineata prefers Membranipora while Onchidoris muricata is known to prefer another bryozoan, Electra pilosa. Electra, Membranipora, and Onchidoris are all now found in the Gulf of Maine while Polycera is not. We tested whether Onchidoris would (1) eat Membranipora at all, (2) eat Membranipora and Electra at different rates, and (3) show a preference for eating Membranipora or Electra when given a choice. We found that Onchidoris does eat Membranipora, and it generally eats Membranipora faster than Electra. However, when given a choice, Onchidoris prefers Electra. Onchidoris typically reproduces in the spring and grows over the fall and winter, but has recently been found reproducing in the winter in New Hampshire. Although it does not survive the winter as well as Electra, Membranipora is the dominant organism living on many macroalgae in the late summer and fall. Thus, the large Membranipora food source now available in the summer and fall may allow Onchidoris to reproduce earlier.
  Biological Invasions 01/2007; 9(6):645-655. · 2.90 Impact Factor