General issue- Common species becomes fragmented- loss & gain of populations

[shoban]

There was a lot of discussion in the guidance document and on several meetings about species that were once common or fairly common and are now fragmented into (many) populations that no longer receive gene flow.  This is a difficult situation for our indicator 2 because one interpretation of this situation is a historical single population, then fragmented into perhaps 20 populations, and now 5 of those populations have gone extinct, leaving 15 populations.  Has the number of populations increased from 1 to 15?  Has it gone down from 20 to 15?  This is challenging for the indicator 2, which mostly assume that historic populations existed and were then lost.  Discussion ensued about how to address this.

On guidance document, under Section 8: "In such cases you should enter a narrative text into “Section 8: Additional information on species range."

Sean Hoban  1:15 PM Oct 12

: I think this is the only spot where we could list 'complicated' situations such as you've suggested Joachim in which the species was once common then became highly fragmented, or went through other dynamics including recovery. I don't know of a way to quantify such situations although I know such situations happen in many species!

Joachim Mergeay • 1:42 PM, Oct 12 (CDT)

I think the best strategy is to include (in the narrative) EOO and AOO: these situations will imply major changes in both.

Rebecca Jordan • 5:12 PM, Oct 12 (CDT)

Quantifying essentially qualitative data is tricky and I don't have a neat solution. I like the suggestions in the text and from Joachim. They'll allow us to at least capture what knowledge is there and then we can later review and determine how best to assess it. There may be a common thread across all this type of data that we can leverage to make some conclusions or assessments from.

Catherine • 5:39 AM, Oct 13 (CDT)New

I agree that this is likely the best solution that we can provide, under the circumstances: as Rebecca says, it is essentially sometimes going to be a matter of trying to quantify qualitative information. This is certainly something that will be useful material for the Discussion section of the corresponding paper (as we will have additional specific examples by that state, too).

Sean Hoban • 9:02 AM, Oct 13 (CDT)New

Well, EOO and AOO will tell us if a species is wide ranging and fragmented (high EOO, low AOO) but not if that has changed over time.  The present state of these variables does not tell us anything about change.  The one question that could tell us about 'overall decline' is under indicator 2, "If available, please record the overall decline in species' habitat area."  Which requires a percent decline (e.g. reduction). This is probably the closest we can get to recording overall decline that does not actually result in 'population losses'

Alicia Mastretta • 2:12 PM, Oct 19 (CDT)New

We should also keep this thread for further discussion and/or add it to the guide.

Sean Hoban • 9:51 AM, Oct 26 (CDT)New

I am now moving this conversation to the google group!

[shoban]

Ivan Paz-Vinas

but maybe reporting aside statistics on the total of landscape covered / mean area occupied per population would help, if available or computable. This may inform whether an increase in the number of populations is due to demographic/geographic expansion, or to habitat loss and fragmentation.
e.g. historically, 10 pops occupied 10,000 km², each pop in a mean of 1,000 km² . Currently 20 pops, occupying 10,000 km² or less --> strong reduction of mean area per pop due to habitat fragmentation/loss

Sean Hoban

Mar 3, 2022

Ok got it. In such case though, what would the 'number of populations lost' be? Maybe have option for reporting EITHER number of populations lost or decline in range size?

Jessica da Silva

Mar 10, 2022

I think we can report on populations gained, and explain this was due to fragmentation. So instead of the proportions of populations remained being 40% or 100% it would be 150%, for example.  If geneflow is halted, I would call these new populations valid populations. If this information is coupled with population sizes we might see that the population size estimates for the historical populations, would show larger sizes; whereas the new populations would show smaller sizes. So even though there are now more populations, they are more at risk of extinction....hypothetically. We could also incorporate a measure of AOO if known.

I suppose in the same vein, this could also track native aliens/extra-limitals. But in this case, the population numbers and sizes would increase.

If assessments get redone for species, this can be added as part of the explanation....i.e., whether this change is a good or bad.

Linda Laikre

Mar 10, 2022

Yes, one option would be to report either number of populations OR change of range size. If the latter it would be good if we could relate the range size reduction to some meaningful entity of the species at hand. One thing could be to translate it into neighborhood size (area equivalent to x number of neighborhood sizes for that species). We have done such analyses for pike doi: 10.1111/j.1365-294X.2005.02570.x and moose DOI:10.1093/jmammal/gyv146 using methods led by Diniz Filho:  https://scholar.google.com/citations?user=scYHGuQAAAAJ&hl=en

[FUKAYA Keiichi]

In my opinion, indicators must conform to the order of the good and the bad of the situation; indicator values should not go up when the situation gets worse and vice versa.

So I would suggest that the value of indicator 2 is 1 -> 1 (or 1 -> 0.x if the area of the population is available) if one large population at the reference time point is fragmented into several at the next time point. In other words, in this case, the fragmented population is considered to be maintained anyway and the indicator conservatively represent the maintenance of the status quo.

Similarly, when two populations at the reference point are merged into one population at the next time point due to the expansion of the population range, the index value would be 2 -> 2 (or 1 -> 1 if the indicator value is scaled to a proportion). Since both of the original two populations are maintained, the indicator conveys the status quo (conservatively because the situation is actually getting better).

Such a treatment may seem somewhat tricky, but it would be possible given that we use geographic information of populations at the reference time point.

2022年11月1日(火) 4:41 shoban <sho...@mortonarb.org>:

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[Ishihama Fumiko]

I think extent-based (distribution-range-based) evaluation could be a solution.

Change in distribution range has been a candidate for calculation of indicator 2 in the earlier stage of developing the indicator.

Though it requires additional input for Kobo, the benefit of this approach is that it can avoid difficulties in defining populations.

Another benefit is that it can avoid confusion about differences in the definition of "populations" for calculating indicators 1 and 2.

(consideration for contemporary (indicator 1) vs historical (indicator 2) gene flow)

 

2022年11月2日水曜日 9:49:48 UTC+9 fuka...@gmail.com: