Occupancy modeling session at NABS/ASLO 2010

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Occupancy modeling session at NABS/ASLO 2010

Postby Trey » Tue Mar 31, 2009 5:17 pm

Hi all -

I am new to occupancy modeling, but am looking into trying to apply it to a variety of questions in aquatic community ecology. As far as I know, very few aquatic types are employing these approaches (though I know mark-recapture is a common population estimation method in fisheries science). I think this is largely because they are not aware of its applicability (I know I wasn't).

I am interested in putting together a special session at the upcoming joint meeting of NABS (a stream ecology society) and ASLO (lake/marine ecology) in June 2010 to introduce occupancy modeling to the stream and lake ecology world. I'm looking for contact information for folks that are using OM to address interesting (aquatic ecology) questions. If I can find enough speakers, I think it will be an excellent session.

Thanks in advance for your help.

Cheers,

Trey
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Postby dhewitt » Tue Mar 31, 2009 6:21 pm

Trey -

I've had a similar recent history with OMs as a fisheries person. We organized a symposium at the American Fisheries Society annual meeting in Ottawa last year on modeling and model selection and we included a short session of 3 presentations on occupancy models. Our stuff may be of interest to you. The big finish was provided by Jim Peterson from Univ of Georgia -- he gave an excellent demonstration of what can be done in stream fish ecology with multi-state multi-season OMs.

Our symposium stuff can be viewed here:

http://www.fisheries.org/afs08/program.html

In the PDF schedule and abstracts we are on pp 18 and 22 (Wed, Aug 20th in Gov General 1). Abstracts are at the end.

Hope this helps,
Dave Hewitt
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Postby Trey » Thu Apr 02, 2009 1:24 pm

Thanks Dave. Looks like an interesting session. It really seems that not many aquatic folks are using OM. I searched the abstracts for the most recent ASLO meeting and the upcoming NABS meeting and found exactly one abstract that referred to OM.
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Two reasons

Postby dhewitt » Thu Apr 02, 2009 2:14 pm

I agree, and I think there are two contributing factors.

(1) As with fisheries catch rate data, people just do the same-ol' and ignore the issue of detection (capture) probability. It's a big deal, so this is sad.

(2) Implementation of OMs in fisheries studies are more tenuous for many reasons (defining seasons and sites, e.g.), and this might put people off, or at least send them running back to the same-ol'.

I hope this changes.
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Re: Two reasons

Postby darryl » Thu Apr 02, 2009 4:55 pm

dhewitt wrote:(2) Implementation of OMs in fisheries studies are more tenuous for many reasons (defining seasons and sites, e.g.), and this might put people off, or at least send them running back to the same-ol'.


See the frustrating thing is that as soon as people start talking about presence/absence situations, you have to have some timeframe and piece of real-estate associated with a 'presence' in order for it to be meaningful. Often this is implicit at best. OM's is a way of getting at presence/absence information, and accounting for imperfect detection (which could be caused by lots of things, not just you not seeing it in the one patch of river gravel you scoop up). When we start rabbiting on about seasons and defining sampling units etc, we're really just trying to formalize things and getting people to think more explicitly about exactly what they mean (and over what timeframe) when they say the species is present at a location.

Darryl
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OMs in fisheries

Postby dhewitt » Fri Apr 03, 2009 2:03 pm

Darryl,

Good comments. I think we've veered off here from the "current opportunities" focus of this section of the forum, but since it's my fault I'll make it worse...

I'm not entirely sure I understand your main point, but I think I hear you saying that people need to, as always, think clearly about whether a particular design/analysis strategy can answer the question(s) they have. I would agree with that whole-heartedly. I've seen situations where fisheries people have tried to force a study into an OM study when it really didn't fit (just wouldn't answer the real question they had) and also situations where their design could be tweaked to do a good job in an OM context and rescue a study otherwise doomed by a lack of dealing with detection/capture probability. Alas, clear thinking about our questions and study designs remains the major hurdle!

Are we in agreement?
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Postby darryl » Sun Apr 05, 2009 5:49 pm

At the risk of a public flogging from Evan, I'll also continue... ;-) Perhaps he might boot this over to one of the other forums.

It's not only fisheries folks that try to shoehorn data into this framework, I've seen lots of people try to do it. Yes, I'm agree with you that people really need to think hard upfront about what biological quantity they're trying to estimate, then design sampling programs that will give them the best chance of doing so.

But my main point before was that if someone samples in an area for 5 minutes and detects the species, and is willing to regard that as a 'presence' (ignoring detectability), do they assume that they have confirmed the species is only present they at point in that 5 minute period, or do they assume that the species is actually present there for some longer time frame (eg a day, week, month, etc). 99 times out of 100 people are probably assuming some longer time frame, which is exactly what the idea of a sampling season is that's required for the OM's. Similar comments hold about defining a sampling unit.
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