John Morgan
Well-known member
Hopefully someone from the BTO will read this and respond helpfully, explaining their rationale. Otherwise, see the PM I have sent to you.
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The rise of the generalists (BTO) (1 Viewer)
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Hopefully someone from the BTO will read this and respond helpfully, explaining their rationale. Otherwise, see the PM I have sent to you.
King Edward
Well-known member
Since I was responding specifically to your assertion that bird feeding causes residents to outcompete migrants, competition between Marsh/Blue Tits is completely irrelevant. As is the effect of climate change on Willow Warblers / Chiffchaffs. So please don't accuse me of 'missing the point' when, in fact, you haven't understood my original question.
Trystan
Well-known member
I'm not sure about anyone missing the point but with regard to comments about feeding I would suggest that Marsh tits are quite happy at bird feeders if the bird feeders are placed in their more 'specialist' environment. Deforestation would therefore result in a decline in Marsh tits but less so in Blue tits.
Chiffchaff and Willow warbler 'compete' for the same food perhaps but that would only become an issue if there was insufficient food. In this case I think the length of migration is far more likely to be a factor as the longer migration increases the risk of passage into or through unsuitable areas i.e. areas which have been changed in some way by man's activities.
Chiffchaff and Willow warbler 'compete' for the same food perhaps but that would only become an issue if there was insufficient food. In this case I think the length of migration is far more likely to be a factor as the longer migration increases the risk of passage into or through unsuitable areas i.e. areas which have been changed in some way by man's activities.
John Morgan
Well-known member
Not totally irrelevant. As Blue Tits are urban and suburban residents, while Marsh Tits are decidedly rural, a parallel comparison with your proposed competitive exclusion of residents over migrants is not at all untoward.
Blue Tit winter survival is hugely aided by garden feeding. 'Surplus', well-fed birds remaining when spring arrives can easily be imagined to head to areas where breeding density is lower, 'artificially' raising it to a level where competition (including Marsh Tits, as the niches will overlap) becomes a major factor in breeding success. Lower success for the BTs is immaterial as they can continue to recruit from the urban/suburban populations. But for the MTs ...
King Edward
Well-known member
It's still pretty irrelevant, since these are related non-migratory species with similar morphology. My point was that many migrants are not so closely related to resident species and have different diets and morphology, hence competition will be small. Maybe there some cases where specific migrant species are being outcompeted by excess numbers of garden-fed residents, but I doubt it's a very significant effect overall.
Dear Ms Davey
I’ve read with interest your article recently published in the journal ‘Global Ecology and Biogeography’, entitled ‘Rise of the generalists: evidence for climate driven homogenization in avian communities’. You are named as the corresponding author, so I offer the following observations for your comment.
The article presents evidence for an increase in species richness/diversity in Britain as measured by the Breeding Bird Survey (BBS) over the period 1994-2006. It also presents evidence for a decrease in a home-cooked ‘Community Specialisation Index’ (CSI), which measures mean habitat specialisation per individual bird recorded in BBS squares, calculated from ‘Species Specialisation Indices’ (SSI), which are coefficients of variation in abundance across habitats.
Your discussion of the results presented is couched in terms of the differences in the response of habitat specialists and generalists to climate change. However the SSI scale is confounded with a range of species variables that could affect response to climate change independently of habitat specialisation/generalisation per se.
You provide SSI estimates for 207 species, and when these are placed in ascending ranked order the number of waterbirds in each quartile is as follows: Q1 (generalist): 7, Q2: 13, Q3: 30, Q4 (specialist): 38. This is to be expected, since by definition waterbirds tend to occur in a restricted range of habitats. However this means that your CSI index is more properly considered as a measure of the prevalence of waterbirds in a BBS square, and the results you present are readily interpretable as an expression of the differing responses of waterbirds and terrestrial birds to climate change in Britain.
A relevant characteristic of waterbirds is that they tend to have a northern distribution, and are therefore more likely to reach their southern limit within the British Isles. The response of waterbirds to increased temperature is therefore likely to be a ‘retreat’ northwards, rather than an ‘expansion’, which could explain the decline in CSI over the study period. The negative relationship between CSI and temperature could also be explained by shrinkage of wetlands with higher temperatures, and the positive relationship between CSI and precipitation by expansion of wetlands with increased rainfall.
If, as seems likely, the terrestrial/waterbird dichotomy is responsible for the patterns presented in the article, it is illegitimate to draw any inferences about the significance of habitat specialisation/generalisation, since the patterns would be absent if the confounding variable were factored into the analysis.
Even if this were not the case, the central inference you draw in the discussion would still be false. This is set out as follows:
“..increases in diversity and richness have been concurrent with declines in community specialisation, suggesting that, although local diversity and species richness are increasing, these gains are likely to be at the expense of specialists in the community”.
No such inference can be drawn, since decline in CSI is entirely compatible with an increase in abundance of ‘specialists’, so long as ‘generalists’ increase more quickly. It is therefore relevant that waterbirds (and therefore specialists) also tend to be large and long-lived, and so respond more slowly at a population level to environmental changes because of their lower intrinsic rate of population increase. The inference drawn would only be supported if you had shown that specialists are generally declining, but no such evidence is presented.
The evidence you do present is therefore completely uninformative about the relationship between habitat specialisation and climate change, and yet you feel able to draw sweeping conclusions such as:
“Our analysis indicates that increases in generalists have concurrent, negative implications for community specialists. This suggests a detrimental impact of climate change on specialist species..”
and
“Range restricted and specialist species are unlikely to have the phenotypic plasticity required to adapt rapidly to novel climatic conditions and habitats and will come under increasing pressure from loss of habitat and the shifting ranges of more generalist species.”
The analyses presented offer no support to these statements, and add nothing to the evidence set out in the citations quoted in their support. The fact that they represent a faithful echo of received wisdom makes this all the more unfortunate, rather than providing mitigation.
I have posted this message on the Birdforum thread discussing your article, and I would urge you to post any response there. I am also forwarding it to Professor Currie, the Chief Editor of Global Ecology and Biogeography, and to the Managing Editor, your colleague at Lund University Martin Sykes, in case they wish to comment on the peer review background and the decision to publish. (I should probably add that there are numerous mistakes in the supporting material, including duplication across columns in tables S1 and S2, and needless use of internal BTO species codes, for which the reference given is incomplete).
http://www.cpbell.co.uk
http://www.youtube.com/CultoftheAmateur
Thank you for copying your letter to this thread. The quotations you use in that letter indicate, sadly, that the above remarks are not so - the offending phrases are in the original article.
John o'Sullivan
Well-known member
Dear Mr Bell,
I have no idea what your post above means. It is way too technical for me to understand without thinking about it more than I want to. This is not a criticism of your post in any way but might explain why my attempted understanding (below) of the reported processes is way of the mark.
I think we are just about the only two truly sceptical critics of the conservation bodies that regularly post on BF although I suspect our motives and perspectives differ in a number of significant ways.
I instintively distrusted the above conclusions as I see much of the environmental research on offer as essentially conservation propoganda.
Conservationists need stuff to protect.
They need special reserves designed to protect particular species. So research showing "specialists" are declining inevitably becomes attempted justification for more specialist reserves and in order to protect the specialists (unsuccessful species) and justification for more control measures of "generalists" (successful species). More funding and an expansion of the conservation empires.
More target species to protect and more target species to shoot.
My simplistic understanding would be that as northern species go north and southern species move north to fill the vacated and changing habitat there has to be a time when species diversity is affected in a number of ways. To begin with species diversity will increase as both the species with more northern distribution hang on, the cross zone species do well and the southern species move in. Eventually however there will come a time when species diversity drops as the northern species disappear. The southern species adapted for what looks like the same habitat but what is fundamentally different (everything is warmer) become the new specialists.
I've noticed a tendency amongst conservation bodies to pretend that the above process is not happening so over the years a variety of Northern species have declined with the conservation bodies significantly underplaying the role of climate change in respect of these observable and widespread changes. All sorts of other reasons are postulated but climate change if mentioned is nearly always right at the end and treated as if it is not important.
I believe they even manipulate the historical data to these ends so the conservation story is that native spoonbills were wiped out by feasting tudors. I would argue that spoonbills did ok in Britain prior to the little ice age when they vanished from Britain. They didn't return until the current phase of climate change when Britain became warm enough for them again. Wouldn't Spoonbills count as a specialist??
I have no idea what your post above means. It is way too technical for me to understand without thinking about it more than I want to. This is not a criticism of your post in any way but might explain why my attempted understanding (below) of the reported processes is way of the mark.
I think we are just about the only two truly sceptical critics of the conservation bodies that regularly post on BF although I suspect our motives and perspectives differ in a number of significant ways.
I instintively distrusted the above conclusions as I see much of the environmental research on offer as essentially conservation propoganda.
Conservationists need stuff to protect.
They need special reserves designed to protect particular species. So research showing "specialists" are declining inevitably becomes attempted justification for more specialist reserves and in order to protect the specialists (unsuccessful species) and justification for more control measures of "generalists" (successful species). More funding and an expansion of the conservation empires.
More target species to protect and more target species to shoot.
My simplistic understanding would be that as northern species go north and southern species move north to fill the vacated and changing habitat there has to be a time when species diversity is affected in a number of ways. To begin with species diversity will increase as both the species with more northern distribution hang on, the cross zone species do well and the southern species move in. Eventually however there will come a time when species diversity drops as the northern species disappear. The southern species adapted for what looks like the same habitat but what is fundamentally different (everything is warmer) become the new specialists.
I've noticed a tendency amongst conservation bodies to pretend that the above process is not happening so over the years a variety of Northern species have declined with the conservation bodies significantly underplaying the role of climate change in respect of these observable and widespread changes. All sorts of other reasons are postulated but climate change if mentioned is nearly always right at the end and treated as if it is not important.
I believe they even manipulate the historical data to these ends so the conservation story is that native spoonbills were wiped out by feasting tudors. I would argue that spoonbills did ok in Britain prior to the little ice age when they vanished from Britain. They didn't return until the current phase of climate change when Britain became warm enough for them again. Wouldn't Spoonbills count as a specialist??
jurek
Well-known member
"diversity of Britain’s birds has increased with a warming climate"
That's what I said for years. Climate change should be positive overall for biodiversity. Increase of warm-climate species, which are far more numerous, should outweigh the decline of cold-adapted species.
common habitat generalists that have expanded their ranges, such as Great spotted Woodpecker - up by 139%, likely at the expense of habitat specialists such as the Grey Partridge and Corn Bunting,
I am hardly, hardly trying to imagine British fields which had Grey Partridge and Corn Bunting in 1994 and in 17 years grown trees so thick that now Great Spotted Woodpeckers live there.
I would say that this depends from land use chage, reforestation and from definition of habitat generalist vs specialist. Ehhh... :-C
Overall, however general trends over broad categories (warm-loving, specialist however you define it etc) are meaningless for practical conservation, because so many species show opposite trends.
That's what I said for years. Climate change should be positive overall for biodiversity. Increase of warm-climate species, which are far more numerous, should outweigh the decline of cold-adapted species.
common habitat generalists that have expanded their ranges, such as Great spotted Woodpecker - up by 139%, likely at the expense of habitat specialists such as the Grey Partridge and Corn Bunting,
I am hardly, hardly trying to imagine British fields which had Grey Partridge and Corn Bunting in 1994 and in 17 years grown trees so thick that now Great Spotted Woodpeckers live there.
I would say that this depends from land use chage, reforestation and from definition of habitat generalist vs specialist. Ehhh... :-C
Overall, however general trends over broad categories (warm-loving, specialist however you define it etc) are meaningless for practical conservation, because so many species show opposite trends.
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jurek
Well-known member
My problem with much of ornithological research is that it predicts nothing of practical value or predictions are so general as obvious.
If a study is to help conservation, it should predict state of things. Bird studies are very poor in this. In this example, knowing if a bird is a specialist or not gives little practical clue to its status. In other studies producing red lists, after few years, it turns that birds selected as most endangerede didn't go extinct, but others slided from the common status all the way to extinction etc etc.
I hope readers understand what I mean.
If a study is to help conservation, it should predict state of things. Bird studies are very poor in this. In this example, knowing if a bird is a specialist or not gives little practical clue to its status. In other studies producing red lists, after few years, it turns that birds selected as most endangerede didn't go extinct, but others slided from the common status all the way to extinction etc etc.
I hope readers understand what I mean.
King Edward
Well-known member
At a national level within, say, Britain or Poland, yes. But globally, not necessarily, since more northerly species will be pushed into decline/extinction by habitat shrinkage and by competition from more southerly species moving north (or up, in the case of mountains).
Or do you take the view that the Arctic is not worth conserving, because not many species live there?
Globally, biodiversity is decreasing rapidly. The fact that overall species counts in particular areas may be increasing due to range expansions caused by introductions and climate change does not change this.
In general, species do not retreat northward because it's too warm, but because at warmer temperatures (or lower rainfall etc.) they are outcompeted by other species which can do better in the changed conditions. The habitat is not 'vacated' first.
On your main viewpoint, what is about biotic homogenisation that appeals to you so much? Do you really want to see the same rats/pigeons/squirrels etc. wherever you go? If you went to visit the Galapagos Islands, would you really want to see only goats rather than giant tortoises and all the other native fauna and flora?
jurek
Well-known member
The study concerned British birds. So, from British-centric perspective, there is every reason to welcome global warming as a boost for birdlife.
Arctic species have vast ranges. So decrease of their range to 50% or more will still mean sizeable population. Arctic almost completely lacks small-scale endemics unlike tropics. No doubt because natural climate variations in the past shrunk Arctic habitats many times.
In fact, I know of no Arctic species which habitat is predicted to disappear completely. Even polar bears, postcard species of warming activists, are predicted to survive with numbers of 7000-8000 by 2050 (assuming global warming didn't stop already in recent years).
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jurek
Well-known member
Wow, what flights of imagination - from British birds to goats in Galapagos!
Biotic homogenization has little to do with global warming. It is caused by man's economy, in these cases importing goats to Galapagos and intensive agriculture plus tree planting favoring woodpeckers over partridges.
I understand that NGOs usually jump on bandwagons - whenever some topic is hot, they try to attach their agenda to it. But in this case it is really linking two unrelated things.
King Edward
Well-known member
The second part of my post was addressed to John o'Sullivan, and was not particularly about climate change.
Regarding species increases with climate warming, my main concern is that climate-related 'gains' should not be considered to offset non-climate-related 'losses'.
Regarding the BTO press release, it was admittedly bad wording that gave the impression that woodpeckers have directly replaced partridges, but it's overly pedantic to focus on this particular comparison rather than their intended meaning, which was that overall habitat changes have favoured generalist species over specialists. It's obviously open to debate whether this is indeed the case, as in CP Bell's criticism above, but there's not much to be gained from debating the rather meaningless woodpecker/partridge 'example'.
Edit: While global warming may increase the total number of birds and other species in Britain, I'm not sure we should be 'welcoming' this. Climate change is a global problem, requiring global efforts to combat it, so in this context I think it would be rather unhelpful for conservation organisations and others to be jumping up and down saying how wonderful it is that all these exotic species are coming to Britain. Yes, it would be nice if Golden Orioles were to come and start nesting in my garden, but that's not something I want at the expense of, say, rainforest endemics going extinct because of climate-related rainfall changes in the Amazon.
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jurek
Well-known member
The whole study depends on quite arbitrary method of designation of species as "generalist" or "specialist". One could say that eg. great spotted woodpecker could equally well be specialist, requiring trees old enough to drill a nest hole, something uncommon in Britain not long ago.
Because one place can support only finite number of species, any conservation "gain" of some species from any cause is connected with "loss" of other species. It's netto balance which counts.
Facts, facts, please. There is a lack of concrete examples of species which would really go extinct (as opposed to losing 10 or 50% of their rather large range).
I would say global warming is an expensive distraction, drawing attention away from more important (but often difficult) habitat conservation, fighting pollution, poaching etc.
Because one place can support only finite number of species, any conservation "gain" of some species from any cause is connected with "loss" of other species. It's netto balance which counts.
Facts, facts, please. There is a lack of concrete examples of species which would really go extinct (as opposed to losing 10 or 50% of their rather large range).
I would say global warming is an expensive distraction, drawing attention away from more important (but often difficult) habitat conservation, fighting pollution, poaching etc.
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King Edward
Well-known member
I am not particularly defending the study methodology, and there is obviously the possibility that a species is designated a generalist on the basis that it's doing well in the modern countryside, and a specialist if it's declining. Great Spotted versus Lesser Spotted Woodpeckers would perhaps be a reasonable species to species comparison - is the latter objectively more specialist than the former?
This rather misses the point, and is contradicted by your final argument that we should focus more on habitat. If species are being lost because of habitat degradation, for example wetland drainage/destruction, then this is a conservation problem which should be addressed (I think we agree here). Otherwise, we could complacently sit back and say "the British fauna overall is increasing, therefore we don't have to worry about conservation because things are improving".
But many tropical species don't have particularly large ranges (as you said yourself previously). Besides which, habitat destruction is likely to interact with climate change by making it harder for species to migrate as their range shifts.
I completely agree that these are extremely important, but that's not to say climate changes should be ignored. In many cases the two (should) go together anyway - oil extraction, transport and use, for instance, is a major cause of climate change and also results in substantial environmental degradation at the same time.
You may have something there, though at the same time it’s important to remember that just because a scientific theory is politically useful, it doesn’t necessarily mean it’s not true. It just pays to be circumspect when judging the value of studies that purport to back it up. Once a theory gains currency, it becomes relatively easy to publish ostensibly confirmatory studies even when, as I believe has happened here, the results provide no objective support.
This is an idea known as the ‘taxon cycle’ hypothesis that was proposed by E O Wilson. It was applied to birds by Robert Ricklefs and G W Cox who interpreted the avifauna of West Indian islands in terms of successive waves of island hopping and competitive exclusion from the South American mainland through the Lesser Antilles, with Cuba and Jamaica as the end point. Amusingly, they failed to realise that Jamaica is part of the continental shelf attached to Central America, and that its avifauna arrived via a land bridge that existed until relatively recently, exposing their reasoning as so much hand-waving.
Undeterred, Cox tried to develop a theory for the development of bird migration based on the taxon cycle. I devoted a good section of my PhD thesis to debunking the theory, for which heresy I was thoroughly denounced by faculty and examiners alike. After unsuccessfully touting my alternative theory around journals for many years, I finally managed to publish it, since when it’s gradually made headway against Cox’s theory. However, it’s always difficult to oppose ideas promulgated by big-name American ecologists and their British lap-dogs.
For the record, I’ve received replies to the mail posted above from David Currie and Martin Sykes, the editors of Global Ecology and Biogeography, providing assurances about the peer-review process for the article. However I’ve received no response or acknowledgement from the author. If this is still the case by the middle of next week, I’ll call Lund University to find out whether there’s any intention to respond, and post the outcome here.
http://www.cpbell.co.uk
http://www.youtube.com/CultoftheAmateur
King Edward
Well-known member
I'm not sure I quite see the relevance of this. Leaving aside the evolution of seasonal migration (since the effect of climate changes should be somewhat similar for sedentary species, plants for instance, which are also moving north), are you saying that northward retreat of species with warming is not caused by them being outcompeted by other species?
I'm loath to make sweeping generalisations, but on the whole I find the idea unpersuasive. What evidence do you adduce in its favour?
http://www.cpbell.co.uk
http://www.youtube.com/CultoftheAmateur
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