Who has an adaptive post-reproductive life-stage?

To establish a case for an adaptive post-reproductive life-stage, one needs to show (at least) the following things:

(1) Prevalence: Across environments, but especially in a wild or non-protected environment, the population experiences more post-reproductive lifespan than is expected due solely to demographic stochasticity.

(2) Utility: Post-reproductive individuals do something selectively advantageous, such as helping younger kin to survive or reproduce.

In many cases, one would like to also address

(3) Advantage: Those individuals who become post-reproductive have a selective advantage over same-age individuals who simply continuing reproducing indefinitely.

However, this third is more complicated, because in many cases there are no individuals who fail to stop reproducing to compare to. For example, 55 year old women giving birth are rare and not easily compared to those who stopped at a more usual time. So testing (3) requires extrapolation and counter-factuals. This assumes that if continuing to reproduce past the current age of cessation were selectively advantageous, that the species' reproductive physiology would allow for it. In many cases, theoretically advantageous traits simply don't exist in the population, and therefore cannot be selected for. If the choice is not between ceasing reproducing or continuing, but rather between ceasing and being useful or ceasing and not being useful, useful wins.

So we are left with basically two fairly simple tests to make decent case an adaptive post-reproductive life-stage. And after some decades of interest in the evolution of post-reproductive lifespan, for how many species has this case been convincingly made? By my count, three. Humans, orcas and a gall-forming social aphid, Quadrartus yoshinomiyai. There are several other likely candidates. Short-finned pilot whales, and possibly other social cetaceans. African and Asian elephants. But I've become very interested in a much more accessible and experimentally tractable species. It lives in multi-generational groups of (very) closely related individuals.  Individuals play subtly different roles in the group throughout their lives. Older individuals stop reproducing and can (assuming no one comes along and kills them) live for extended periods post-reproductively (on the time scale these things live). You may have it in your garden.

Any guesses? Later this week I'll give you the answer.

Progress

For years, I've been worrying about about my chronic backlog of papers I should have written a long time ago and just haven't had time for. I'm very happy to report that my to-write list is getting a lot shorter. Three of the papers on that list will come out in the first half of this year. Number four is currently out for review, 5&6 need to be revised and resubmitted, a seventh is written and currently with colleagues awaiting their comments. The eighth has figures made and large chunks of text in their second or third drafts. If all goes well, all eight should be at least submitted by the end of the year, and I'm guessing that six will have come out. Of course there are several more that I need to get to, and new projects being planned, but it feels good to be clearing the backlog a bit. Especially nice is that after spending too long on methods papers, incidental discoveries and other tangents, the manuscripts I am working on now actually address the central points that motivated the research in the first place.

1. Levitis DA. (2015) Evolutionary Demography: a synthesis of two population sciences. In: International Encyclopedia of Social and Behavioral Sciences, 2nd Edition. ed.: J.D. Wright. (Coming out in May)

I am an evolutionary demographer, and while encyclopedia articles are not my bread and butter, this is very much on topic.

2. Olsen TB, Christensen FEG, Lundgreen K, Dunn PH, Levitis DA. (2015) Coelomic transport and clearance of foreign bodies by sea stars (Asterias rubens). Biological Bulletin. (Coming out in April)

This started as a student project to develop methods for studying the evolutionary demography of starfish, but when it became clear the animals wouldn't stay tagged, my students decided to investigate why. Their result was cool enough that we're publishing it.

3. Oravecz Z, Levitis DA, Faust K, Batchelder WH. (2015) Studying the existence and attributes of consensus on psychological concepts by a cognitive psychological model. American Journal of Psychology 128: 61-75.

My most cited paper (on the biological meaning of the word behavior) is one I started as a graduate student, even before it became clear I would be an evolutionary demographer. It got a nice write-up in the New York Times. Many of those citing it are in philosophy or psychology. A couple of years ago I was contacted by some psychologists who wanted to work with me to reanalyze those data. I never expected to publish in a psychology journal.

4. Zimmerman K, Levitis D, Addicott E, Pringle A. (2014) Maximizing the mean nearest neighbor distance of a trait to choose among potential crosses and design a fully crossed mating experiment.

This methods paper, currently out for review but with an earlier version already archived online and therefore available (journals are increasingly okay with this) grew out of a collaboration that is part of my ontogenescence project. In trying to answer my evolutionary question, my collaborator invented a new method for designing mating experiments, and we wrote it up. 

5. On raven populations in the Eastern US. One reviewer loved it just as it was, the other made numerous (and useful) comments on how to improve the analysis. Being worked on by my colleagues who are primarily responsible for the analysis.

6. Part of the same ontogenescence collaboration as #4, this was just rejected by a high impact journal on the basis that they rejected it (no reason or feedback given, as is common with such journals) and will be submitted to another in April.

7. Another ontogenescence paper, this time in a marine ecology context. Our plan is to submit in May. Between now and then the main order of business is to get feedback from colleagues and use it to improve the text.

8. Same project as #s 4 and 6.

9. On post-reproductive lifespan, building on the papers and methods that came out of my dissertation. We have cool results proving an interesting point, but it still needs a fair bit of work.

They probably won't be submitted in exactly this order, as a lot of it depends on factors beyond my control, but this is more or less the order I'm prioritizing them in. Beyond that it is hard to predict. Some older things I still do really need to write up, some fruitful student projects on post-reproductive lifespan that are looking good, some vague ideas. 

One thing I've decide is that at least for the moment, no papers that are outside the main foci of my research program (evolution of pre-reproductive mortality and post-reproductive survival) are going to make the list. Numbers 1-3 & 5 above don't directly address either of these topics, and 4 is tangential. That is a bad habit, and one I'm going to break.

Why lightning talks work

Last week was the second annual meeting of the Evolutionary Demography Society. It was fabulous. Close to 100 people, over three days, at Stanford. Man there is a lot of good food around there. A friend and I were sitting outside, eating burritos when this dude from a farmers' market booth came over and started giving us samples of gluten-free baked goods. Delicious. Great weather, friendly people. Oh, yes, something else. What was it now? Ah! We talked about a lot of great science. Roughly 70 presentations. Post-reproductive lifespan, evolution of aging, all the topics I like best and every talk on a topic of at least some interest. Fabulous.

Many conferences (but not this one) have what are called concurrent sessions. In one room there might be a series of perhaps 15 minute long talks about matrix models, while in another they are talking about theoretical modelling, and in a third it could be all about field data on hunter gatherers. The benefits of this are allowing more people to give talks in a short period of time, and letting audience members pick and choose which topics they spend their time hearing about. At EvoDemoS, we address these same problems in a very different way. Most presenters give a lightning talk plus poster. The lightning talk is five minutes (plus five for questions), and then after each session there is a break for coffee and posters. But the posters are mostly from the same people who gave the lightning talks, on the same subject. So you get up, give a rapid intro to the work, answer a few questions, and then because there are no concurrent sessions, everyone at the conference knows who you are and what you are working on. If they are interested in it, they come talk to you at your poster. If you didn't bother to print your poster, they already know what you are working on and come talk to you anyway. If they aren't  interested, they don't have to sit through 15 minutes of you talking about it. The frequent and lengthy breaks (made possible by the shortness of the presentations) make it easier to stay alert through the talks, and let us achieve a much higher conversation-to-passive-listening ratio, and it is really the conversations that are the point of the conference for me.

Now the obvious downside is that many speakers are used to having more than five minutes. Some won't come because they can't have more time, use their connections and seniority to push for more time, or simply prepare the same talk they would for a much longer slot and largely ignore the warnings that their time is almost up. One speaker, to remain nameless, was on slide 4 of 26 when the one minute warning came and sped up only slightly. So the moderators need to be a bit firm in some cases. The more senior the speaker, the more likely an overage, in my experience. This is partly a matter of habit, but also that the more senior people often have more work to present. There were a few talks where the theoretical framing got almost completely cut to make time for more methods and results, and that was sometimes problematic. A is consistently greater than B, but what does that tell us? That said, the great majority of the five minute speakers were able to state the question clearly, say a word or two about methods, give a main result (or maybe two) and draw a conclusion or three before inviting us to see the poster. And almost everyone I talked to at the conference, both as speakers and audience, thought it worked well in this context.

For a conference with thousands of people, I'm not sure lightning talks would work. I'd be interested to hear from anyone who has tried it. But for anyone organizing a small conference like ours, I absolutely recommend it.

The Evolutionary Demography Society has a website

I spent a lot of time figuring out that I could very quickly and easily make a website that would suit our needs. I used SeaMonkey but frankly for what I made I could have used anything, down to and including any text editor. Now that I know how simple it is, I could do it again in a day.

The logo I designed for the society probably won't last, as there are far better designers than I involved, but it does the job. 

At some point I will add some pretty pictures of animals and plants.

Oh yes, the url:
http://www.evodemos.org/

The Evolutionary Demography Society is born

We are pleased to announce the formation of the

Evolutionary Demography Society (EvoDemoS)

and to invite interested researchers to join. While many societies include life-history evolution or evolutionary demography within the range of topics they consider, no active society focuses on these topics across taxa and disciplines. EvoDemoS is intended to fill this gap.

EvoDemoS is an interdisciplinary scientific society dedicated to the study of the interactions of ecology and evolutionary biology with demography, including but not limited to patterns of mortality, reproduction and migration over age, stage and state and the evolutionary processes that produce those patterns. All taxa and methodologies are of interest. Our primary goal is to facilitate communication between researchers, and as such we are pleased to offer free membership for 2013 to any interested researcher. We invite members from students to established experts. We will organize yearly meetings to provide a specific forum for evolutionary demography. Our first meeting will be in Odense, Denmark in October of 2013, and will be open only to society members. Membership can be gained by emailing your name, preferred email address, affiliation and a sentence describing your research interests to:
evodemo-list@demogr.mpg.de

Questions and comments can be addressed to this same address.

Please feel free to distribute this announcement broadly.

Sincerely,
The Board of the Evolutionary Demography Society


President
James W. Vaupel, Max Planck Institute for Demographic Research and University of Southern Denmark

Vice President
Shripad Tuljapurkar (Tulja), Stanford University

Secretary/Treasurer
Daniel A. Levitis, Max Planck Institute for Demographic Research and University of Southern Denmark

Board Members
Anne M. Bronikowksi, Iowa State University
James R. Carey, University of California, Davis
Hal Caswell, Woods Hole Oceanographic Institution
Charlotte Jessica E. Metcalf, University of Oxford
Tim Coulson, Imperial College London
Timothy Gage, State University of New York at Albany
Jean-Michel Gaillard, Université de Lyon and Centre national de la recherche scientifique
Thomas B. Kirkwood, Newcastle University
Daniel H. Nussey, University of Edinburgh
Fanie Pelletier, L'Université de Sherbrooke
Deborah Roach, University of Virginia
Rudi G.J. Westendorp, Leiden University

Brave=Denotation(Foolish)-Connotation(Foolish)*2

When colleagues started telling me that what I was doing was brave, I knew I was in trouble. People tell you are brave as you march off to war, or volunteer to babysit multiple toddlers around bedtime, or (it seems), when you undertake the organizing of a new scientific society. They mean, "Man, you're going to end up unemployed, but I'm sure glad you are doing it instead of me."

I waited until they had a few drinks in them and had mostly finished going back for seconds on the salmon, then commandeered one of the cocktail tables as a podium. I proposed the formation of an society and then opened the floor for discussion.

The good news is that we now have about 50 members including many of the big names in the field. The bad news is that everyone seems to think I have an actual plan. How will we fund the first meeting? What kind of official and financial structure should we have? Will we take over that other, mostly defunct but somewhat related society for the benefit of their infrastructure and their resources, or will we start fresh? Do we need to incorporate? I don't know any of these things.

So here is what I am doing. I'm organizing the election of a board, and I'm making sure there are people who know what they are doing standing for election. I'm communicating with the people who will organize the first meeting next year. I want the society to exist, and I'm happy to help, but I certainly don't plan to run the thing by myself. That would be a little bit too brave.

Accepted, but...

We have set ourselves a difficult task. Some months ago, my friends and I submitted a review article, clarifying some common (within the scientific literature) misconceptions, to a very good anthropology journal. Today we heard back from them. The editor explained that it took longer than usual because he had sent it out to "several" reviewers, and then "several more" and was waiting to get comments from all of them.

The good news is that all the reviewers seemed to like it, and the editor knows which issue of the journal he wants to put it in, which we take as the paper being accepted. The bad news (or at least time-consuming news) is that all of the several and several reviewers made long lists of things they would like to see changed, added, clarified or reorganized. I have not yet finished reading all these comments, but I don't see a lot of repetition, meaning that we have hundreds of distinct comments and criticisms to deal with. In the months we were waiting, we also showed the draft to a couple of colleagues, who gave us still different but also very useful comments. The good news is that the editor has given us permission to go well beyond the usual page limit for this journal in order to deal with all the reviewer comments. The bad news is that we now can't use space limitations as an excuse for not dealing with relevant points or citing relevant literature. So we have a great deal of rewriting to do.

Part of the problem with writing an article pointing out places where other people's thinking or language has been unclear is that one has to live up to very high standards for clarity in one's thinking and language. We've already extensively rewritten this paper a few times, and each time it has gotten clearer. Nevertheless, a large portion of the reviewers' comments are right on, and further clarification is needed. By the time this thing comes out it will either be brilliant or a total muddle. I'm not clear which.

Spanning the vastness

When I was but a lad, my siblings and I used to accuse my father of knowing everything, a charge he would always deny, observing that even excluding those things which are not known to anyone or are secret, and restricting ourselves to academic knowledge, there is more to know than any one person or any thousand people could possibly know.

To see why this is so, consider the sheer volume of scientific literature being produced. ISI Web of Knowledge, an online tool used primarily by scientists for finding scientific literature relevant to their work, indexes the contents of over 23,000 academic and scientific journals. Many lesser known, newer or otherwise less main-stream or traditional journals are not indexed at all. One needs to go to other databases to find information published in books, or in dissertations, or, or, or.

Like my father (as I am in most things), I find myself far too mortal to know any meaningful fraction of anything, even if we restrict ourselves just to academic biology. I'd say there are roughly 8000 peer-reviewed journals in which biological work is regularly published, and if you add up all the papers I skim through, it is probably the equivalent number of pages of the output of two or three of these. The papers I read in detail if assembled together would surely make up much less than the output of a single journal. And I put more time into reading and therefore less into writing than is optimal for my career.

One result of this is that I frequently find out that there exist thriving sub-disciplines of biology of which I have almost no knowledge. For example, only last week I for the first time heard the word "metabolomics." Google Scholar lists over 6000 papers in the last year on this rapidly expanding field about which I know no more than I could guess based on the name.

My knowledge of transcriptomics was quite as absent three years ago. Transcriptomics is the study of RNAs in the cell, generally in the context of gene expression patterns. I became interested in transcriptomics because I proposed that mortality risk during embryonic development would be highest at those stages at which gene expression patterns were changing fastest. I was a doctoral student at the time, and my adviser asked me if there was any way of testing this idea. I had to admit I didn't know if it was possible to test because I didn't know enough about the field I have since learned is called transcriptomics. The answer is that yes, there is a way of testing the idea, but it will cost a couple of hundred thousand dollars, and require collaboration with people who read different journals than I do. I will never be an expert in transcriptomics, but I can find a colleague who is, but has little knowledge of evolutionary demography, and invite him to collaborate on a project that combines our expertise. And this is why science can be a somewhat unified pursuit despite having far more product than one person can read even the titles of.  

I referred in my last post to one of my advisers at Berkeley, and one of my all around favorite human beings, Ron Lee. Ron would always advise me to think about my relative advantage, by which he meant I shouldn't just work on the most interesting or best questions, as there are far too many. Rather, I should choose among them by considering which questions I was better placed, given my strengths and resource, to answer than was anyone else likely to work on the question. Ron's advice has always served me well, and so I do consider this before starting any project. Frequently, as with this developmental transcriptomics and demography project, my relative advantage arises from the fact that I am combining two fields separated enough that no one else is likely to ask the question any time soon. Evolutionary demography and developmental biology do not, as a rule, talk to each other. Many fields of biology have almost no communication with each other, leaving vast unexplored interdisciplinary territories (unless that is all in some set of journals I haven't come across yet).

Etymological challange: Evolutionary Demography

I have a bit of a stomach bug this weekend, so I am thinking about things that don't require so much concentration. A colleague had raised the question of when the term "evolutionary demography" was first used in print, and said that the oldest example he could find was:

Caswell, H. 1985. The evolutionary demography of clonal reproduction. pp. 187-224. In: J. B. C. Jackson, L. W. Buss and R. E. Cook (eds.) Population Biology and Evolution of Clonal Organisms. Yale Univ. Press.

I, currently having more time than brain power, did a little bit of searching, and found this:

Wilbur, H.M. 1975. The Evolutionary and Mathematical Demography of the Turtle Chrysemys picta. Ecology, Vol. 56, No. 1 (Winter), pp. 64-77.

which uses the phrase "evolutionary demography," explicitly in the acknowledgements and implicitly in the title.

Can anyone find an older explicit recorded use of the phrase? If so, the commenter presenting the oldest confirmable example will win a prize: I will personally make a sculpture representing a species of your choosing (excepting diatoms) and send it to you in recognition of your etymological achievement. Comments will be accepted for one month from today, or until I get the first winning example, whichever comes last.

What is EvoDemo?

The question has arisen how we should define Evolutionary Demography, such that we can decide if someone's work qualifies. I have offered 2 short definitions, into which I haven't yet put a lot of thought.

Short definition 1 : Scientific study which combines evolutionary biology and demography.

Short definition 2: The study of the evolutionary history, function, variation and relevance of demographic traits.

These are both broadly phrased. I don't like constraining definitions to the traditional terrain. A zebra found outside Africa is, in my opinion, still a zebra. As such, I haven't included anything about what traits, methods, etc. evolutionary demographers usually consider.

My question to you, dear readers, is: Can you think of anything that should be considered evolutionary demography that doesn't qualify under these definitions, or anything that shouldn't qualify that these definitions let in?

The demographics of evolutionary demographers

A group of us considering organizing a new scientific society have been compiling a list of those we would like to invite to the initial meeting of the society, to be held here in Rostock, probably next year. We are up to 125 people (excluding people who work here, as everyone who works here will be invited). The group making this list is about half male, half female. The list is 100 males and 25 females.

Why this skew? We each listed people whose names came to mind, and in some of the subfields we are drawing from (e.g., mathematical ecology) almost all of the well known people are male. Higher level academics in general still skew strongly male, and the higher the level the stronger the skew, in most cases. This is both a cohort effect (older cohorts of scientists are both more well known and more male) and a selection effect (males find it easier to advance up the ladder). Being demographers, we are very much aware of this, and are very much interested in having a diverse society, but it is not clear what we can do about it. There is also a preponderance of Europeans, North Americans and East Asians; again this is unintentional and difficult to reasonably address.

Despite these skews, it is a wonderful list of researchers, and I hope we can get most of them to attend.

Acronymic Challenge

As a grad student, I operated independently enough, and had a large enough group of undergraduate assistants, that I decided to pretend I had my own institute. I named it the Dissertational Institute for Evolutionary Demography, and believe me, I worked for that acronym.

Some colleagues and I are now discussing starting an actual scientific society for evolutionary demography, and it needs a good acronym. I suggested Society for Ecological and Evolutionary Demography (SEED) but was shot down on the grounds that I had added Ecology to the society just for the acronym. So I'm still thinking here, and wonder if you have any good ideas.

It has to have the words "Evolutionary Demography" in it and some word that means society or association. It can have the word "International" if the I helps. Keep in mind that this is going to be an actual scientific society, so nothing ridiculous, scatological or overtly jocular will do.

Now, I should clarify I'm not actually in charge here, so I don't necessarily get to pick the name, but if you propose something sufficiently clever, appropriate and memorable, I'll propose it, and you may have the honor of naming a scientific society.

Excited to teach again

Summer Semester 2011

IMPRSD 189
Introduction to Evolutionary Demography

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Start:	4 July 2011
End:	9 July 2011
Location:	Max Planck Institute for Demographic Research (MPIDR), Rostock, Germany

Instructors:

• Daniel Levitis, MPIDR
• Hal Caswell, Woods Hole Oceanographic Institution
• David Thomson, University of Hong Kong
• Annette Baudisch, MPIDR
• Alexander Scheuerlein, MPIDR
• Oskar Burger, MPIDR
• Maren Rebke, MPIDR

Course description:

Understanding survival, reproduction and other life-history events is central to the study of both demography and evolutionary biology, and each field has developed methods and concepts to observe patterns and elucidate principles. The growing field of evolutionary demography treats demographic variables (patterns of survival, reproduction, and development) as properties of organisms that reflect evolutionary processes, just as morphology, behavior, and physiology do. It draws on both disciplines to search for evolutionary explanations of demographic patterns in terms of adaptation, genetics, phylogeny, and the environment. Further, it applies demographic methods and reasoning to answering evolutionary questions. Demography and evolutionary biology are conceptually unified and inextricably linked, so the questions we want to answer can best be tackled by traversing traditional disciplinary boundaries. This course is intended to introduce early career researchers from both fields to the concepts, methods, challenges and questions of evolutionary demography.

Course structure:

We will begin with an introduction to classical evolutionary demography and the motivations for combing evolution and demography, incorporating enough basic evolutionary theory and demographic theory to get everyone on the same page. We will then focus on current topics in evolutionary demography, including:

• Aging across the Tree of Life: Measures and Patterns
• Sex-specific differences in mortality patterns: Evolution in action
• Modes of adaptive explanation of demographic patterns: a survey
• The pace and shape of aging
• The evolution of mortality of the young
• Age specific reproduction in the wild
• Life-history allometry and Charnovian invariants

Finally, pairs of students will be asked to spend the afternoons of the 7th and 8th preparing short presentations, to be presented on July 9th. Each pair will discuss the evolutionary basis of a different demographic trait or phenomenon, what is known about it and how it can be investigated.

Organization:

For July 4-8, each morning will consist of two lectures (one hour each) and each afternoon will have a one hour lab. Then the afternoon of July 9th will be occupied with short presentations by pairs of students.

Prerequisites:

Students should be familiar either with the basics of demographic life-table methods, or with evolutionary theory. Familiarity with Stata or R software will be very helpful.

Examination:

Students will be evaluated on participation in class and on short presentations.

Financial support:

There is no tuition fee for this course. Students are expected to pay their own transportation and living costs. However, a limited number of scholarships are available on a competitive basis for outstanding candidates.

Recruitment of students:

• Applicants should either be enrolled in a PhD program or have received their PhD.
• A maximum of 16 students will be admitted.
• The selection will be made by the MPIDR based on the applicants’ scientific qualifications.

How to apply:

Applications should be sent by email to the MPIDR. Please begin your email message with a statement saying that you apply for course IMPRSD 189 - Introduction to Evolutionary Demography.

• You also need to include the following three documents, either in the text of the email or as attached documents. (1) A two-page curriculum vitae, including a list of your scholarly publications. (2) A one-page letter from your supervisor at your home institution supporting your application. (3) A one-page statement of your research and how it relates to course IMPRSD 189. Please indicate whether you would like to be considered for financial support.
• Send your email to Heiner Maier (office@imprs-demogr.mpg.de).
• Application deadline is 31 March 2011.
• Applicants will be informed whether they will be admitted by 15 April 2011.

Readings:

The course will make use of readings from:

• Baudisch, A. 2011. The pace and shape of ageing. Methods in Ecology and Evolution. DOI: 10.1111/j.2041-210X.2010.00087.x
• Caswell, H. 2001. Chapter 11, Matrix population models. Sinauer.
• Jones, O. R., Gaillard, J. M., Tuljapurkar, S., Alho, J. S., Armitage, K. B., Becker, P. H., Bize, P., Brommer, J., Charmantier, A. & Charpentier, M. 2008 Senescence rates are determined by ranking on the fast-slow life history continuum. Ecology Letters 11, 664-673.
• Levitis, D. A. 2011 Before senescence: the evolutionary demography of ontogenesis. Proceedings of the Royal Society B: Biological Sciences 278, 801-809.
• Metcalf, C. J. E. & Pavard, S. 2007 Why evolutionary biologists should be demographers. Trends in Ecology & Evolution 22, 205-212.
• Rebke, M., Coulson, T., Becker, P. H. & Vaupel, J. W. 2010 Reproductive improvement and senescence in a long-lived bird. Proceedings of the National Academy of Sciences 107, 7841-7846.
• Vaupel, J. W., Baudisch, A., Dolling, M., Roach, D. A. & Gampe, J. 2004 The case for negative senescence. Theoretical Population Biology 65, 339-351.

Additional reading material will be provided at the beginning of the course.

Finally out

This is the first of my dissertation chapters to be published. It is good to have it out. It is in a new Journal called Methods in Ecology and Evolution. It seems like it will be a very good journal, but it is too soon to know for sure.

A measure for describing and comparing postreproductive life span as a population trait

Summary:
While classical life-history theory does not predict postreproductive life span (PRLS), it has been detected in a great number of taxa, leading to the view that it is a broadly conserved trait and attempts to reconcile theory with these observations. We suggest an alternative: the apparently wide distribution of significant PRLS is an artefact of insufficient methods.

2. PRLS is traditionally measured in units of time between each individual’s last parturition and death, after excluding those individuals for whom this interval is short. A mean of this measure is then calculated as a population value. We show this traditional population measure (which we denote PrT) to be inconsistently calculated, inherently biased, strongly correlated with overall longevity, uninformative on the importance of PRLS in a population’s life history, unable to use the most commonly available form of relevant data and without a realistic null hypothesis. Using data altered to ensure that the null hypothesis is true, we find a false-positive rate of 0·47 for PrT.

3.  We propose an alternative population measure, using life-table methods. Postreproductive representation (PrR) is the proportion of adult years lived which are postreproductive. We briefly derive PrR and discuss its properties. We employ a demographic simulation, based on the null hypothesis of simultaneous and proportional decline in survivorship and fecundity, to produce a null distribution for PrR based on the age-specific rates of a population.

4.  In an example analysis, using data on 84 populations of human and nonhuman primates, we demonstrate the ability of PrR to represent the effects of artificial protection from mortality and of humanness on PRLS. PrR is found to be higher for all human populations under a wide range of conditions than for any nonhuman primate in our sample. A strong effect of artificial protection is found, but humans under the most adverse conditions still achieve PrR of >0·3.

5.  PrT should not be used as a population measure and should be used as an individual measure only with great caution. The use of PrR as an intuitive, statistically valid and intercomparable population life-history measure is encouraged.

One of my goals in this paper was to show how badly some evolutionary questions need demographic methods. I think we accomplished that.

Concepts in the evolution of senescence about which I am increasingly skeptical:

Intrinsic vs. Extrinsic mortality
Optimality hypothesis
Mutation Accumulation hypothesis
Agonistic Pleiotropy hypothesis
Disposable Soma hypothesis
Caloric Restriction Effects
"Rate of living" hypothesis

This list includes most of the theoretical basis for the field

ixNay on the ifeLay istoryHay volutionEay

I have been doing a lot of reading of the life-history evolution literature. It turns out there is a lot of it. About 1200 papers are published each year in journals followed by Web of Science using the phrase "life history evolution." These are in a hugely wide range of journals. What I am coming to realize is that the phrase has been overused and broadened to the point that it is nearly meaningless. A study of egg size relative to adult size can be labeled life-history evolution. A study comparing daily activity patterns between males and females can be labeled life history evolution. A study of age at first reproduction can be labeled life-history evolution. Perhaps more troubling for the field, life-history evolution has come to be viewed very much as natural history is. Natural history, the basic facts about what a species does, what the individuals and groups are like, what their habitat is and so on is tremendously important to know when studying a species, but it doesn't get grants, citations or jobs because it is often only relevant to those studying that particular species, and the methods and conclusions are rarely ground breaking. Life history evolution has come to be seen in the same way, likely explaining why there is no journal society or regular meeting for Life History Evolution.

This stigma may help explain why so few biologists wade into the deep rich pools of unasked questions lining the boundaries between evolutionary biology and demography. Such work is quickly labeled as life-history evolution, and despite being novel, important and of general interest, suspected of having the same failings as the rest of the field. The name demographers prefer for this intersection, evolutionary biodemography, does not on the face of it sound like a task for biologists. As I learned from Crayola, green-blue is a type of blue, not a type of green. Evolutionary biodemography is by extension part of demography, not part of biology. This thinking applies despite the fact that many of the publications in evobiodemo are from biologists rather than demographers.

I briefly mentioned some of this to my boss, who is a demographer by training, but one of the leading advocates of the idea that demography and biology need to learn from each other more. He suggested I organize a small conference at the institute, inviting both biologists and demographers. The institute has had these types of meetings before, mostly inviting established people who already blend the two fields, and interesting papers and collaborations have come out of it, but little lasting progress. The people who were already aware of both fields remained aware of both fields, and those who weren't continued not to care. So my thought, now that I've been invited to organize a small conference, is to invite biologists and demographers early in their careers, who work on similar topics, but within their own fields. A few biologists who work on juvenile dispersal patterns, and a few demographers who work on juvenile dispersal patterns, each of which may have little awareness of the fact that other people in the other field wonder about remarkably similar questions. Other sets who work on infant mortality, population responses to natural disasters, cohabitation, etc. Let them present their work, let them make the explicit case of what the other field can learn from them, and then let them present on what they would like to know or get from the other field. A workshop on demography and evolution for early career scientists. I'll add it to my to do list.

EvoDemo: "Senescence rates are determined by ranking on the fast-slow life-history continuum"

Jones, O.R., Gaillard, J.M., Tuljapurkar, S., Alho, J.S., Armitage, K.B.,
Becker, P.H., Bize, P., Brommer, J., Charmantier, A., Charpentier, M.,
Clutton-Brock, T., Dobson, F.S., Festa-Bianchet, M., Gustafsson, L.,
Jensen, H., Jones, C.J., Lillandt, G., McCleery, R., Merila, J., Neuhaus, P.,
Nicoll, M.A.C., Norris, K., Oli, M.K., Pemberton, J., Pietiainen, H.,
Ringsby, T.H., Roulin, A., Saether, B.E., Setchell, J.M., Sheldon, B.C.,
Thompson, P.M., Weimerskirch, H., Wickings, E.J. & Coulson, T. 2008.
Senescence rates are determined by ranking on the fast-slow life-history continuum.
Ecology Letters.

Abstract:

Comparative analyses of survival senescence by using life tables have identified generalizations including the observation that mammals senesce faster than similar-sized birds. These generalizations have been challenged because of limitations of life-table approaches and the growing appreciation that senescence is more than an increasing probability of death. Without using life tables, we examine senescence rates in annual individual fitness using 20 individual-based data sets of terrestrial vertebrates with contrasting life histories and body size. We find that senescence is widespread in the wild and equally likely to occur in survival and reproduction. Additionally, mammals senesce faster than birds because they have a faster life history for a given body size. By allowing us to disentangle the effects of two major fitness components our methods allow an assessment of the robustness of the prevalent life-table approach. Focusing on one aspect of life history - survival or recruitment - can provide reliable information on overall senescence.

Keywords: Aging; comparative analysis; demography; generation time; metabolic rate; senescence

Comments: One of the authors is applying for a position here in the next few days.

The Meta-Journal of EvoDemo

I've often complained that there is no journal of evolutionary biodemography, or life-history evolution. I've decided to do something about this, sort of. I'm starting a new series here on Blog of Science! in which I post the abstract to published papers of interest and link to the online versions. If I get ambitious I may include some comments or criticisms. In part this will just make it easier for me to keep track of what I've read and what I thought of it. In part it will help motivate me to look for relevant literature. Perhaps it will even be useful to others. Posts like these will be tagged with EvoDemo.