Today we had an interesting seminar with Julie Lockwood from
Rutgers University. Her talk title was
Killing the cuddly: Tactics for managing exotic predators to protect their
native prey. Her talk was divided into
two sections the first dealt with the importance of model choice in providing
guidance to managers and the second part dealt with attempts to understand
population growth in invasive species.
Importance of modeling
She motivated the first part of her talk with an empirical example from
Rayner et al 2007. This manuscript looks
at the breeding success of Cook’s petrels under three conditions first prior to
any work being done to remove predators so that both cats and rats were
present (success=.25-.50), then after cats had been removed but rats were still present (success=0.0-.25), and then
finally once both had been removed (success=.50-.75). Here
is the graph that she showed from that paper:
She then explained that most model informed management
decisions that are currently made use models that only examine the predator
population and look for the life stage that can be targeted to most quickly
reduce its population. She suggests
instead we need to take a more nuanced approach with a more complex model and
use the target of keeping the prey alive rather than dropping the population of
predator as quickly as possible.
She then described work that developed a model that
allowed the predator to effect the prey population size. This model can accommodate biological
realities such as the fact that often juvenile predators can’t eat adult prey
or that only certain stages of prey are targeted at all. Once this model was developed they did a
series of full block experiments with short, medium, or long lived predators and
prey for a total of 9 pairings. The
general results of this were that particularly in the case of long lived
predators traditional approaches and her recommended approach found
different optimal solutions.
- my biggest question from this part of the talk was: Can we wrap in two predators and get the "right" solution to the motivating example of Cook's petrels?
Population Lag
The next part of her talk was focused on population
lag. This is a well documented
characteristic particularly in invasive plants. It is characterized by a species being present at low density
for an extended period of time and then at some point suddenly exhibiting a
great increase in population size. In
plants it appears that population lag can range from as little as a decade to
as long as a century or more. The data
available for vertebrates though was less clear. Primarily because there are not large numbers
of vertebrates that have been introduced with abundant data on population size
over time. However, Hawaiian birds offer
the opportunity to study this phenomenon.
Her team used the Audubon Christmas bird count data to look at population dynamics of 54
invasive species in Hawaii.
I’ll be honest this part of the talk got a little fuzzy for
me. The data are very noisy and so
apparently some method was used to define a maximum population size and data after
this point were discarded (I believe). The remaining
data were fit with a number of models 1) simple linear, 2) log 3) two
piece linear. For the two piece linear
basically every point between the 6th year and the 5th
year prior to peak population was tried as the break and the break that resulted in the highest likelihood
was kept. If the single break model was
better than the alternatives then that was evidence for population lag in that
species. Her results indicated that most
species did exhibit a population lag.
- my biggest question/comment from this part of the talk was: Seems like one of those places where we need to develop or assess model adequacy, I could picture the best model here being too poor to reveal biologically important characteristics.
All in all this was a really interesting talk. My final take home from the talk was that most invasive
species provide us with a long period of time when population grows slowly and
during this time careful modeling can provide us with the best chance of having
a successful attempt in controlling an invasive species. In addition even if we miss this low population window populations are stochastic and so perhaps we should be prepared to attack an invasive when it experiences a natural fluctuation.
Here are links to the Lockwood lab and the pages of her two former students who did much of this work. My explanations above are no doubt over simplifications and contain errors which are purely my own. If this stuff really interests you check out the publications below which contain the research I described above.
-->
Orin Robinson
cheers
Great article!! Thank you for your post. This is excellent information. It is amazing and wonderful to visit your site.
ReplyDeleteupvc sliding doors in hyderabad
upvc sliding door suppliers
upvc doors and windows manufacturers