Top Down Effects of Snakes

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Bryan Hamilton
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Top Down Effects of Snakes

Post by Bryan Hamilton » March 18th, 2015, 8:52 am

Finally some strong evidence...

Snakes can control prey populations and pythons in the everglades are impacting their prey. I've been interested in this for a while. The everglades pythons seemed like a great model to test top-down effects of snakes.

Abstract
"To address the ongoing debate over the impact of invasive species on native terrestrial wildlife, we conducted a large-scale experiment to test the hypothesis that invasive Burmese pythons (Python molurus bivittatus) were a cause of the precipitous decline of mammals in Everglades National Park (ENP). Evidence linking pythons to mammal declines has been indirect and there are reasons to question whether pythons, or any predator, could have caused the precipitous declines seen across a range of mammalian functional groups. Experimentally manipulating marsh rabbits, we found that pythons accounted for 77% of rabbit mortalities within 11 months of their translocation to ENP and that python predation appeared to preclude the persistence of rabbit populations in ENP. On control sites, outside of the park, no rabbits were killed by pythons and 71% of attributable marsh rabbit mortalities were classified as mammal predations. Burmese pythons pose a serious threat to the faunal communities and ecological functioning of the Greater Everglades Ecosystem, which will probably spread as python populations expand their range."

http://phys.org/news/2015-03-invasive-b ... marsh.html

http://m.rspb.royalsocietypublishing.or ... 0.full.pdf
Edited to update link

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gbin
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Re: Top Down Effects of Snakes

Post by gbin » March 18th, 2015, 12:37 pm

I don't think this will surprise too many people - except those who for one reason or another are in denial about the pythons' harmful effects in the Everglades (hi, Ernie!). But it's definitely good to have such direct evidence, both for evaluating the Everglades situation and for addressing the larger scientific question. Thanks for bringing it to our attention, Bryan! :thumb:

Gerry

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WSTREPS
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Re: Top Down Effects of Snakes

Post by WSTREPS » March 18th, 2015, 6:11 pm

Data bending as it was so aptly put by Gordon Rodda in his USDA published paper once again rears its ugly head. No doubt this new study will fall flat on its face under further scientific scrutiny as all the other work produced by the various glades python researcher's has.

This paper was no surprise , as a matter of fact it was sadly predictable . Gordon Rodda laid the ground work on Guam with yet another brown tree snake study in 2012 (I think) that was a primer for this latest foray into scaring up funding for the researchers. Researchers who are running out of straws to grasp at . Every time they run into the theater shouting fire and it turns out there's no fire they lose a few more friends, less and less people are listening to them because they have proven themselves dubious characters . Over 6 million dollars spent so far as its been reported

AND,

What the research has produced has been,

wildly inaccurate climate matching maps based on horrendously misrepresented data, giant cages of snakes freezing to death only to have the researchers go on about how the snakes can survive in "temperate climates", books that from cover to cover are filled with erroneous information, bounty hunts that produce virtually no snakes, a research study to prove that snakes are hard to find, little dogs that find no snakes, radio tracking projects that divulge no new information, published papers filled with contradiction , errors and poorly conducted science fed to the press, Gordon Rodda and others lying about what was said to the press, Mike Roachford making up a story (like NBC's Brian Williams ) about how he was in the helicopter when the famous exploding python/alligator picture was taken, Grossly erroneous information found in university data bases, works expedited thru the peer review process or completely bypassing the process and on and on.

The bottom line is they have nothing to hang their hats on, they cant find any real problem but there is no way they will admit to this , they have to much to personally gain ( career wise ) they must convince people no matter what, to give them financial backing.

The motives are clear, the long time and highly regarded shark researcher Aidan Martin to his credit spoke candidly about what goes on in the field of biological research. I placed the word python in parentheses next the word shark. You can substitute python for shark as the issues he discuses are universal.
Shark (python)research is expensive and few things are harder to do than to get someone else to pay to satisfy your curiosity. In many cases, officials in charge or granting funding for scientific research do not understand the science a fraction as well as the applicant, so the onus is on him or her to explain convincingly why a proposed line of research is significant, what results can be expected, why this knowledge is important, how much it will cost, and — above all else — why it is worthy of their financial support. It is therefore not enough to know your field and be able to explain it clearly but also to be able to pitch a proposed line of research with all the skill of a top-ranking salesperson.
Aidan Martin shark researcher
Publishing the results of research is how a shark (python)biologist advances his or her career. This requires a whole different set of skills. First and foremost of these is the ability to organize raw data into a standardized format followed by scientific journals. This is good for their careers because it makes them seem highly productive (granting committees find it much easier to count an applicant's number of publications than to evaluate the validity and importance of each one),

Aidan Martin shark researcher
Then there's the human side of things. As in every other job, there is dirty politics, cut-throat competition, roaring egos, rampant jealousy, nasty or unfounded rumors, petty grudges, character assassinations, betrayals of trust, theft of work or credit, and other perils of dealing with people. Don't get me wrong, there are also unexpected kindnesses, incredible generosities, mutually beneficial alliances and collaborations, and sometimes deep friendships to distil out of working with other people. But often you never know who's going to do what until after they've done it and it seems that unpleasant surprises are far more common than pleasant ones. Such are the problems inherent to working with others' ambitions and insecurities. The problems seem to intensify in high-profile matters, such as those concerning White Sharks (pythons)or shark attacks.
Aidan Martin shark researcher
There are plenty of ethical, meticulous, hard working, thoroughly wonderful people working in shark research who do what they because they love it. But, far too often, the work of these dedicated scientists seems to be overwhelmed in the public eye by relatively few self-styled shark (python)researchers who are unethical, methodologically sloppy, thoroughly untrustworthy ratbags and posers who care nothing for the ideals and practices of Science but do what they do because they want attention and adulation. Ratbags are often skilled politicians and can be tough to identify until after they've shown their true motives.
Aidan Martin shark researcher
The most high profile people that are or have been involved with the pythons in the everglade's, People such as Gordon Rodda, Bob Reed, Mike Dorcus, Skip Snow, and the list of others associated with these people are what Aidan Martin so perfectly describes as "Ratbags".

Ernie Eison

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regalringneck
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Re: Top Down Effects of Snakes

Post by regalringneck » March 19th, 2015, 3:40 am

... well i certainly didnt see any strong evidence; one was a link to a log in @ BYU ( & they dont want me :p ) the other a short piece in a e-physics blog; that describes 77% of a not released number of morts derived from apparently 40 marked bunsters that were apparently free released into two areas (that likely already had an extant pop of marsh rabbits), then that 77% value is contrasted to a 71% predation value of yet another unreleased number (total mortality in marked rabbits) due primarily to mammalian predation; not a particularly robust study design IMO.
Python researchers would more likely answer these questions via changes in the body condition of the pythons themselves & tracking antibody titers in the mesocarnivores ... The fact that we're not hearing about changes in the frequency of DoR pythons on the flamingo rd., probably tells us all we need to know about this plague of pythons ...

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gbin
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Re: Top Down Effects of Snakes

Post by gbin » March 19th, 2015, 6:06 am

WSTREPS wrote:The motives are clear...
If we're talking about Ernie, yes, his motive for using FHF's message boards to wage an unending campaign of misrepresentation and otherwise dishonest denigration against scientists/scientific work that focus on the Everglades python situation is quite clear. As I've pointed out elsewhere:
gbin wrote:[Ernie Eison] and [David and Tracy] Barkers' many years spent trafficking in pythons has enabled them to learn a fair bit about these snakes, without a doubt, but his and the Barkers' profound vested interest - not to mention his profound dishonesty in defending that vested interest from perceived threats (I won't speak to the Barkers' methods, as I'm not nearly so familiar with them as I am his) - unfortunately means that no one should trust anything Ernie Eison has to say on the subject of FL's pythons or the scientists/research focusing on them.
. . .
regalringneck wrote:... The fact that we're not hearing about changes in the frequency of DoR pythons on the flamingo rd., probably tells us all we need to know about this plague of pythons ...
I'm not following you here, John. Can you explain your point for me?

I think you should cut the researchers at least a bit of slack, by the way. After all, it's pretty hard to carry out studies of predator-prey relationships in general, not to mention to demonstrate direct effects of predation on prey populations. I reckon anyone looking for slam-dunk evidence is expecting (insisting upon?) too much. It's evidence nonetheless, and it's accumulating. That's mostly how science works.

Gerry

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Bryan Hamilton
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Re: Top Down Effects of Snakes

Post by Bryan Hamilton » March 19th, 2015, 8:05 pm

Its amusing to think about working with high profile wildlife as a high paying glory fest. I was (and still am) interested in working with tigers and grizzly bears. I've dabbled in rattlesnakes, mountain lions and bighorn sheep. These charismatic megafauna present quite a few challenges. Pythons and sharks are similar.

These are not easy species to get experience and funding to study, nor to publish peer reviewed articles on significant biological questions. Its hard to get in and even harder to get big enough sample sizes to say much about your study system. Small mammals, bats and song bird are much easier to work with (especially for a phd student or tenure track professor). Insects and fish are that much easier. I really admire the folks that make such sacrifices.

Its also amusing to think that the Everglades python situation isn't worthy of study or funding. Even the most anti-science folks in our society would probably say "Hhhmm, large contrictors introduced into a national park that we're spending billions to restore, a warming climate, bordered by high human population densities? We should probably study that...."

regalringneck wrote:... well i certainly didnt see any strong evidence; one was a link to a log in @ BYU ( & they dont want me :p )

Python researchers would more likely answer these questions via changes in the body condition of the pythons themselves & tracking antibody titers in the mesocarnivores ...
I updated the link so it should go to the open access pdf of the journal article. Our tax dollars at work.

What do mesocarnivore anitbody titers have to do with invasive pythons?

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regalringneck
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Re: Top Down Effects of Snakes

Post by regalringneck » March 20th, 2015, 4:34 am

Morn'n Bryan & thnx for editing the link, an interesting piece of work no doubt & one that will now nest w/ 30 other files in my 42 gig+ floridapythons folder :}

Despite the authors assertion :

"Our research clearly establishes pythons as a
causal agent of marsh rabbit declines, a species we selected
because of its theoretical resilience to predation pressure
[16,17]. Accordingly, pythons are a logical and likely explanation
for the observed declines in less fecund mammalian
python prey species found in ENP (i.e. raccoon Procyon lotor,
round-tailed muskrat Neofiber alleni, bobcat) [8]."

I suggest this effort falls short of establishing "causality" & is in fact another relatively shorterm correlative study that would appear to have been designed with the apriori presumption that the pythons were the only variable that needed to be controlled/factored into the analysis.

My preliminary criticisms based on 1 reading would be;

A) There is not enough (any) discussion of the release sites characteristics amd obviously if they differ, so will the likely results.

B) It appears 75% of the releasable rabbits were released on the control sites ???

C) Their was no attempt by the investigators to model the surviving rabbits production.

D) That their was no discussion (nor comparison to other cottontail studies) that in both control & python plots their was a nearly identical 85% loss of marked rabbits/~ 9 months.

E) Figure 2 appears to indicate a major uptick in losses to pythons between 250 & 300 days, yet the control risk is flatlined thru that same period, a highly unlikely result given the life cycle of a cottontail.


Re: Dr. B's ? ; Where is the DoR table [thru time; 10 yrs +] for flamingo rd; this is the no-brainer 50 mi controlled transect thru the park & the fact that this data is either not being collected (shame) and/or not being released (2x shame) indicates to me, its not useful for the current narrative under construct.

Re: BH ?; I've long noted mammalian carnivores populations ( occasional exception of coyotes) tend to cycle widely & often for years at a time. Purported declines in everglade carnivores should be investigated utilizing various antibody levels along w/ other ecological parameters.

None of which puts me in any frame of thought to doubt the liklihood that these pythons are likely doing real damage to the endotherms of the everglades.

Does anyone know what the python count was on the "plowed field incident at froggy bottom" that happened in ~ 2006 before the big freeze and what the size of the plowed area was? That was the event where the bobcat claw was fd in a pythons stomach.

OK time to locate more java :p

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gbin
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Re: Top Down Effects of Snakes

Post by gbin » March 20th, 2015, 6:30 am

Bryan Hamilton wrote:Its amusing to think about working with high profile wildlife as a high paying glory fest. I was (and still am) interested in working with tigers and grizzly bears...
My wife and I actually started our scientific careers working on Siberian tigers, Bryan, albeit in a captive setting. (Had a chance to do my Ph.D. work on Sumatran tigers in the wild, but turned it down because of who I'd have had to accept as my major professor.) Nope, no riches to be found there. ;) You, I and others - probably even including Ernie Eison, in his occasional moments of clarity and honesty - know that this kind of work is done for love, not money.

I think your criticisms are certainly worth considering, John. Of course, pretty much every scientific study is worthy of criticism - and far too close to every scientific study contains assertions by its investigators that run ahead of the study's data ;) ; as you know, the trick is to examine the data themselves and the methods used to obtain them (not so much the conclusions accompanying them), and unless the methods were too seriously inadequate, to incorporate the data into that which came before. Bricks being laid down to build an edifice of knowledge, increasingly useful as construction continues...

I'm honestly not sure what to think about your python DOR question (if I understand correctly that you're wanting to see what's showing up in their stomach contents). I agree that could be very useful information(!), don't understand why it's not being published (!!) and would be dismayed if the reason is because it's not being collected(!!!).

Gerry

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regalringneck
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Re: Top Down Effects of Snakes

Post by regalringneck » March 20th, 2015, 7:55 am

... ok let me try this again; Flamingo Rd is the main park rd (hwy) out of Homestead, It is a 50+ mile paved transect thru the heart of the everglades. There are traffic counters on it. There is a visitors station on it. Park personnel & other agencies + the public & python researchers drive it daily. Pythons presumably get run over on it ( tho the two i found in 800+ miles of s florida roadcruising were not on this road!).
There is no reason there shouldn't be a log spanning 15 years indicating where & when pythons have been seen live or dead, how big they were, & perhaps how long the carcass persisted on the roadway. Ideally gut contents would have been examined, but thats probably asking too much from most.
What I have asked for before, but no ones responded, is what this data looks like, of particular interest to me would be the before & after numbers for the big freeze of 2010. If the Park Superintendent has'nt made this an assignment to all park personnel, shame on her. The primary indicator of a major future problem would be a substantial increase in juvenile pythons. If the DoR's are not increasing through time & indeed if they've become substantially reduced since 2010, then I would have less concern & would tend to lean towards their eventual extirpation.
One fellow who wrote the 1st paper on the decline of the everglades mammals from driving surveys on this road, omitted as i recall, any python data from his report! edit; went back & reviewed Holbrook's paper he reports 6 live pythons for 9 survey efforts; he didnt collect DoR data.
Yes a good edifice is what we're all wanting, but theres no point laying good bricks ... on a foundation of straw (groupthink) ...

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gbin
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Re: Top Down Effects of Snakes

Post by gbin » March 20th, 2015, 8:27 am

Ok, I believe I understand you now, amigo. Curse this stilted electronic communication medium! :x

I agree that information on DOR pythons themselves could be useful, especially if the data point toward a young and growing population or (wish-wish...) a population crash, as you mention.

But I think information on their gut contents would actually be much more useful, and well worth the effort involved. Our principal concern over the pythons being in the Everglades is, of course, what they might (I strongly suspect are) doing to the overall ecology and especially to certain species there. All the more so given our present uncertainty about these effects. Gut contents and their change through time could tell us quite a bit - and about as directly as it gets ;) - about the (relative) abundance of the species the pythons are preying upon and how their abundance might be changing through time. If I were in FL working on Everglades pythons, this is certainly a place where I'd be focusing some effort. (Well, I'd be focusing some students' effort on it, but you get my point. :) )

Gerry

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Bryan Hamilton
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Re: Top Down Effects of Snakes

Post by Bryan Hamilton » March 20th, 2015, 11:25 am

I don't know why the stomach content data hasn't been published. That's an interesting question. I did a stomach content analysis on brown tree snakes in 1999 and by that time most of the birds were already extinct. I found a feather in a sample which was a big deal.

Stomach content analyses have all kinds of problems but an analysis of the DOR python data seems ideal. Feeding ecology studies usually start with an analysis of museum specimens and anecdotal observations. Its a real luxury to be able to sacrifice every single snake you find. That is an incredibly rich data set that I hope was carefully archived for just this kind of work.

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Re: Top Down Effects of Snakes

Post by gbin » March 20th, 2015, 12:36 pm

My thoughts, exactly.

Gerry

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Re: Top Down Effects of Snakes

Post by narrowfellow » March 21st, 2015, 7:09 am

deleted

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Re: Top Down Effects of Snakes

Post by regalringneck » March 21st, 2015, 12:33 pm

Thnx for responding NF, sounds like you are there amongst the pythons, & research, so i ask you; What you've experienced on the Flamingo Rd & for how long? I agree w/ most of your comments, other than we differ on the value of the DoR pythons, as one can safely predict when a predator depresses or eliminates their prey base (almost always a situation limited to exotics), changes to the predator's body condition & fecundity are soon apparent. All the pixs i've seen thus far of florida pythons indicates few have missed a meal.

From the paper ; "Within these areas, we captured rabbits
on levees that provide an elevated platform where the rabbits
congregated. We also captured rabbits from the shoulders of
roads where the dominant vegetation was brush broom grass
(Andropogon spp.) and Brazilian pepper trees (Shinus terebinthifolius "

Do you know if the release sites were characterized by this same elevated flora? The paper indicates this is unlikely as it states ; " Increased water levels did not appear to have a substantial
influence on python’s predation of marsh rabbits (electronic
supplementary material, table S3). As both species are
strongly associated with water, it is possible that rising
water levels had little influence on how accessible marsh
rabbits were to pythons."

I hope too you'll care to comment on some of my other points / questions posted above ? thnx.

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Bryan Hamilton
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Re: Top Down Effects of Snakes

Post by Bryan Hamilton » March 21st, 2015, 1:23 pm

I finally finished the "Marsh rabbit mortalities tie pythons to the precipitous decline of mammals in the Everglades" paper. I thought the authors made a very compelling case that pythons were responsible for both the declines and near extirpation of rabbits and that python predation continues to keep rabbits from recovering in the national park.

As I mentioned above, I'm really interested in top down regulation of prey by snakes. One the one hand we regularly talk about how valuable snakes are for controlling rodent populations, while there is very little evidence that snakes can actually control prey. This study is one of a handful that has been able to demonstrate prey control by snakes.

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Re: Top Down Effects of Snakes

Post by Jimi » March 24th, 2015, 10:42 am

As I mentioned above, I'm really interested in top down regulation of prey by snakes.
I was glad to see the manipulative experiment with rabbits. Strong evidence, strong inference. I really didn't care for that mammal roadkill paper a few years back, I thought it was pretty crap for a number of reasons.

Perhaps NF can provide some ~ recent links or citations to evidence along these lines from Guam. I recall from my ~ 2001 pre-thesis-project lit review, as well as short-term immersion in the BTS research & management environment, that there were numerous observational lines of evidence of BTS regulation of prey populations/availability.

One of the more readily-apparent lines of evidence was the disparity in max size attained in rural vs urban BTS - to get the big ones you had to go to town, where prey densities were heavily subsidized by e.g., garbage, and presumably snake densities were suppressed by e.g., roadkill. Out in the boonies they're all runts. Also it seemed there was feedback of the sort RR mentioned - poor body condition and "terrible" (low) reproductive ability in BTS. Possibly there's also some boom-bust cycling going on between predator & prey populations.

Possibly the "closed-population" study site offered some more direct evidence? Since absolute BTS densities were known, every individual was marked, and - I think - growth & survival rates were known due to constant sampling inside the fence. NF, I think Bryan would be really interested to hear about the closed-pop site, and any publications or grey-lit reports resulting from it.

here's a link to a slightly older closed-pop paper: https://www.fort.usgs.gov/sites/default ... /22004.pdf

cheers,
Jimi

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