Tag Archives: Biology

Can we just agree on a name?

An image of a squirrel with personality

A squirrel with personality, from jpaxonreyes (used under a CC license). Because let's face it, this post needs a picture.

Looking at the email alerts I get for new journal issues, I came across a new paper by Sih et al. in Ecology Letters [1], looking at the “ecological implications of behavioural syndromes”.  And I suppose that I could talk about the content of the paper, but what I’d rather do instead is go off on a short rant about research on this topic, as is my right as a blog writer.  What’s got a bee in my bonnet (and why am I suddenly 90 years old)?  It’s the name, “behavioural syndromes”.  It drives me mad.  I’ve seen papers refer to the topic by:

  • “Animal personality”
  • “Behavioural syndromes”
  • “Coping styles”
  • “Animal temperament”
  • “Interindividual variation” – not an SEO friendly description, to be sure.

There seems to be a political aspect to this too, but I’m not 100% clear on it.  Some themes are clear, though.  My feeling is that Sih seems to be pretty stuck on “behavioural syndromes”, while others like Denis Réale (whom I know from my Ph.D. at UQÀM) and Neils Dingemanse seem to be throwing spaghetti at the wall; after trying to introduce “animal temperament” as a thing – which, as far as I can see didn’t take hold – they had the (actually quite inspired) idea of doing an end-run around the whole thing by combining personality with plasticity and coining the new phrase “behavioural reaction norms” [3].  Only time will tell if that one takes off.

Lest you think that it’s just a name problem, it seems that confusion in the names is a symptom of deeper confusion over what they’re studying and how to study it.  Hanging around at a couple of the discussions at the last ISBE made it clear that people working in this field aren’t agreeing on the name, the definition, or the methodology (statistical or experimental).  Some of this is cause for excitement, of course:  when you’re this confused, it’s probably a sign that you’re on to something good.  And don’t think that I’m writing the area off;  there’s been a lot of exciting work in personalities over the last decade or so.  Hell, I’m trying to get a paper published on the topic myself right now.  Yet, I can’t help feeling that work in this area is going to be a little bit hamstrung until it converges on clear values for each of these things.

And honestly, I just feel sorry for the next poor sod who wants to do a literature review or meta-analysis.  So, can we just agree on a name and call it a day?

—-

[1]. Andrew Sih, Julien Cote, Mara Evans, Sean Fogarty, and Jonathan Pruitt. Ecological implications of behavioural syndromes. Ecology Letters, 15(3):278–289, 2012.

[2]. Denis Réale, Simon M. Reader, Daniel Sol, Peter T. McDougall, and Niels J. Dingemanse. Integrating animal temperament within ecology and evolution. Biological Reviews, 82(2):291–318, 2007.

[3]. Niels J. Dingemanse, Anahita J. N. Kazem, Denis Réale, and Jonathan Wright. Behavioural reaction norms: animal personality meets individual plasticity. TRENDS in Ecology and Evolution, 25(2): 81–89, 2009. 

Tagged , ,

What is an animal’s “choice”?

Image by loryresearchgroup

In behavioural ecology, we face a number of limitations in trying to ferret out the relationship between behaviour and evolutionary forces.  These range from the philosophical and theoretical (e.g. what makes a behaviour adaptive or an adaptation?) to the mundane and methodological (is that experimental set up really measuring aggressive behaviour?), and solving these problems is one of the most pressing tasks facing a behavioural ecologist attempting to make useful statements about a behaviour’s evolution.  However, while some of these issues are recurrent and obvious, others are more subtle and can sometimes slip under the radar.  One such problem is the topic of a recent paper by Véronique Martel and Guy Bovin, published recently in the Journal of Insect Behaviour and entitled “Do choice tests really test choice?”  (DOI: 10.1007/s10905-011-9257-9).

The thrust of their argument is that there is a difference between “apparent choice”, and “true choice”, which is driven largely by the fact that we can’t ask animals what they would have done under different circumstances.  As Martel and Bovin point out, animals may make one choice when presented with a particular set of stimuli, or resources as they call it (which may mimic natural conditions!), but express a different preference when presented with a larger set of resources, or when the conditions of the choice are changed.  They distinguish three characteristics of a true choice, only one of which is met by an apparent choice:

  1. The choice must be non-random, i.e. that individuals must choose one resource more often than the others;  testing only this criteria means that researchers are measuring apparent choice, while this is a necessary but not sufficient criteria for true choice.  (I would add to this that the choice probability should be fairly stable if the animal is made to choose under exactly the same conditions).
  2. The choice should be the same even in the “absence of a differential response by the resource” (p. 332). The authors state this to avoid situations in which the resource (e.g. a potential mate) is manipulating the choice of the focal animal, a problem which reminds me very much of the literature on animal signalling.
  3. It should be demonstrated that every resource is perceived, to avoid issues of sensory bias and the like.  It strikes me that this criterion will be hard to meet;  for example, if while testing mate choice the researcher tries to demonstrate a lack of bias by showing responses by the focal individual to each of the potential mates in isolation, how does that prove that one or more of the potential mates aren’t being ignored when the focal individual is given the choice between all of them?
As the authors state, meeting criterion 1 is sufficient for an apparent choice, but 2 and 3 are required for a true choice.  They spend the bulk of the rest of the paper giving examples of both apparent and true choice and elaborating the differences between the two.  It should be noted that they are not claiming that one type of methodology is “better” than the other;  in fact, they take pains to point out the pros and cons of both.  Here’s an example:

The importance of distinguishing between apparent and true choices depends on the objective of a study. If the objective is to establish which resources will be exploited under natural conditions, then the apparent choice is appropriate. If the experimenter wants to know which female will be mated by a male in a natural situation, then the results of this test (the apparent choice) will provide the answer. However, if the objective of the experiment is to establish the mechanisms of this choice, then it becomes important to look more closely at the results. If a male does not perceive a mated female as a resource because she does not produce sex pheromone, the male is thus inseminating virgin females as they are the only resource perceived. In this case, an apparent choice (the virgin female) is expressed, but this choice is the result of the non-perception of the mated female, which prevents this apparent choice from being a true choice. Measuring an apparent rather than a true choice does not remove the relevance of the test, but only modifies its interpretation. Consequently, it is important for the experimenter to state a clear question before identifying the adequate experimental setup to use.

I think that it’s important to mention here that the ideas expressed in this paper aren’t terribly groundbreaking;  a number of people ranging from economics to psychology to behavioural ecology have, at one time or another, made largely the same argument or a variation thereof (one example of a related problem is raised by a really smart guy, Jeffrey Stevens, in this book chapter here).  In fact, I’m a co-author on a paper currently in press at Behavioural Ecology talking about this issue from the opposite direction, wherein we argue that the mechanisms that underlie behaviour may be constrained and that these constraints need to be taken into account when assessing the evolution of behavioural outcomes[1].  I even made an argument very much like the one in this paper during my Ph.D. synthesis exam!

Having said that, I like the paper for its laser-like focus on raising awareness about a very specific part of animal behaviour and cognition that can seriously undercut the conclusions drawn from experimental or field work if the appropriate test isn’t matched to the hypothesis the researcher wishes to explore.  I suspect that their definition of apparent and true choices is incomplete and leaves out issues that will be hashed out in future papers, but if the journey of a thousand steps has to start somewhere, it’s not a terrible first stride.
——–
[1]. I’ll write more about this here when the paper is published.

Tagged , ,

Death in the nest: trade-offs rule the day.

Underlying many research programs in biology is the meta question: why is there more than one type of X?  (In continuous form, why is there variation in X?)  This question recurs in many areas of animal behaviour, and indeed in the entirety of the study of evolution itself.  Some examples include:

  • Why do animals show variation in “personality” – why are some consistently more aggressive, more exploratory, bolder, etc.
  • Why are there more than one type of male that females select between?  Why are some “attractive” and others “unattractive” – why aren’t they all attractive? (Sexual selection).
  • If aggressive signals like roaring can make other animals give up a resource or back down from a fight, why don’t all animals use the aggressive signal?  Why is there variation in signal type when all animals should use the same signal, which would then lose all meaning and be ignored?
  • Why do some animals invest heavily in each offspring while others produce as many as they can and invest very little in each?
The general response to most of these questions hinges on the idea of a trade-off.  In its most basic form, a trade-off involves giving up one thing to get (or avoid) another.  In particular, animal behaviour often hinges on cost-benefit tradeoffs.  It is desirable to have some trait or perform some behaviour, but doing so may come with a cost if we have too much of the trait or perform the behaviour too often or at all.   Examples of this litter the pages of any textbook in the biological sciences, from molecular biology up to zoology and ecology;  in particular, we can begin to address the questions I listed above by appealing to trade-offs:
  • Some personality types, like aggressive or exploratory, can confer benefits – such as always winning fights or being the first to find food – but also come with costs – such as the injuries from always fighting or the cost of being eaten while you try to be the first to eat.  Some individuals will be willing to make this trade-off, others will not.
  • The answer to this question has filled entire bookshelves, but here’s one tiny example:  in 1975, Amotz Zahavi published a landmark paper proposing that attractive males are “handicapped”;  they willingly trade off the cost of the handicap for the increased number of matings of come with it.  Zahavi’s “handicap principle”  suggested that this was a reliable indicator of quality to females because only some males would have the required quality (be strong enough, fast enough, etc) to bear the cost of the handicap in order to reap the benefit.
  • One of the most well-known answers to this question began the field known as evolutionary game theory;  at the end of the 1970s, the tragic figure of George Price and the eminent John Maynard Smith answered the question by showing mathematically how frequency-dependence could lead to a trade-off between Hawks, who are aggressive, and Doves, who back down at the first sign of trouble;  when Hawks are extremely common, their aggression leads them into costly fights against each other, which reduces the benefit of aggressiveness and makes Dove-ish behaviour more attractive.  But when Doves are common, Hawks get immense benefit with no cost by bullying Doves around.  (There’s actually significant overlap between this point and the previous, but that’s a topic for another blog post!)
  • An entire branch of evolutionary biology, life history theory, deals with questions like this:  in the face of limited resources, how do individuals make choices about the timing and sequence of events in their life to maximize their fitness?

This general pattern underlies the story behind a neat new advance-access paper from the groups of Alex Kacelnik and Juan Reboreda that manages to give away the good stuff in the title:

Ros Gloag, Diego T. Tuero, Vanina D. Fiorini, Juan C. Reboreda, and Alex Kacelnik. The economics of nestmate killing in avian brood parasites: a provisions trade-off. Behavioral Ecology, 2011.

Here, the question of types and the answer of trade-offs arises in the context of brood parasitism.  Brood parasites are organisms – birds, fish, insects – that relieve themselves of the responsibility of parenthood by tricking other organisms into doing it for them.  In birds, this usually takes the form of brood parasites laying their eggs in other species’ nests, where the enterprising young tykes then pretend to be the offspring of the unlucky suckers who are to play host.  Brood parasites can be specialists that only parasitize the nests of a target host species (or small group of species); an example of this is village indigobirds, who generally parasitise fire-finches (and who also display an interesting mechanism where the young copy the songs of the host species).  Generalists, on the other hand, will parasitise a range of host species;  cowbirds, for instance, are generalists.  Brood parasites can also vary in whether they eliminate the other offspring of the host that they have colonized (nestmate killing) or whether they attempt to blend into the crowd (nestmate tolerant).  To make this more concrete, take a look at this short video showing a newly-hatched cuckoo ejecting a reed warbler chick from the host nest:

The paper I’m talking about here explores an interesting question about brood parasites, namely:  why are some brood parasites nestmate tolerant while others are nestmate killers? Gloag et al. propose a mathematical model that explains this in terms of a “provision trade-off”.  Host nestlings can help the newborn parasite by stimulating the host parents to bring more food than the parasite could solicit alone, and if the parasite can outcompete its nestmates for that additional food, then it does better to let them live.  Thus the trade-off:  when the host offspring increase the fitness of the parasite, it lets them stay, but otherwise it kills its flatmates.  Gloag et al. take the time to break this trade-off down into its constituent parts, namely (in their words, p. 2):

  • The total provisioning rate stimulated by the whole brood, and
  • The share of the provisions received by a parasite nestling.
The simple model they derive shows that when the ability of a parasite to stimulate food provisioning by the host parents is greater than its ability to compete for food with its nestmates, the parasite will do best if it is reared alone and the murder spree begins.  This relationship depends on the interaction between these two variables;  in other words, “[i]f each host nestling causes a greater increase in provisioning than the amount it consumes, then the presence of host chicks would result in higher consumption for the parasite, even if a host chick takes a bigger fraction of the extra food than the parasite.”  The model helps to predict where each scenario – nestmate killing or tolerance – is plausible as a function of this intuitive trade-off.
VIRA-BOSTA (Molothrus bonariensis)

VIRA-BOSTA (Molothrus bonariensis) by Dario Sanches, on Flickr

Gloag et al. then use this model to explain differences not only intra-specific differences between specialist species in their level of nestmate tolerance, but also inter-specific differences within generalist species as well.  This would have been a good paper even if they had stopped there, but they then go on to test their ideas in the field using a generalist parasite, the shiny cowbird (Molothrus bonariensis). Working in South America, they searched for the nests of two types of shiny cowbird hosts, chalk-browed mockingbirds and house wrens, and set up two experimental conditions.   In the “mixed group”, the a single cowbird egg was placed among host eggs, and in the “alone” group, the cowbird eggs were placed in the host nest with dummy eggs so that the cowbird young would be reared alone.  They measured the food amount and quality brought to the nest from video recordings, and measured the physical quality of the resulting offspring (weight and tarsus length).  They also compared the mortality rates of the cowbird chicks to see if there was a difference between the conditions.  Their findings?

In our field study, nestmate tolerant shiny cowbirds encountered both sides of a provisions trade-off depending on the host used. When reared by chalk-browed mockingbirds, nestling cowbirds had higher food consumption, mass gain, and survival when alone in the nest than when sharing with 2 mockingbird young. In contrast, cowbirds reared in the nests of house wrens had higher food intake and growth when reared alongside 3 or 4 host young than when reared alone. (p. 7).

The results of their work suggest strongly that there is a trade-off at work here, and that the virulence of parasite offspring will be affected by the provisioning characteristics of the host environment.  Of course, they are quick to suggest that there are other factors potentially at work in differential growth rates, such as thermoregulation (larger broods can help each other thermoregulate) or size of the nestlings.  Nestling size is an interesting issue, because as the authors mention, cowbird young are larger than house wren nestmates but equal in size to or smaller than their mockingbird counterparts.  This may the competitive ability of the young either through physical competition between nestlings where size would be important, or because parents preferentially feed larger offspring.  (As a by-product, this also raises the longer-standing question of why host parents don’t do a better job at discriminating among their young for parasites in the first place;  for an explanation in terms of yet another trade-off, I’d refer you to this letter to Nature by Arnon Lotem as a possibility).

Wilson's Warbler feeding it's Cowbird chick  "offspring"

Why are you feeding this monster? (by Alan Vernon, on Flickr)

The work on trade-offs in this paper provide a simple and intuitive model for the action of brood parasites across a wide variety of situations, and then back it up with empirical data that demonstrate this trade-off in action.  It’s hard to ask for more from a paper!  Of course, as with every paper you’ll ever read, “more research is needed” (we have to say that, or we’re straight out of a job, aren’t we).  It wil be interesting to see if this trade-off does actually hold in other species, and combining the principles in this paper with a phylogenetic analysis would make for a fascinating approach. In the meantime, though, if you’ve read this far I’d urge you to take the lesson of this paper to hear and learn to look for the trade-offs inherent in many biological systems.  As a guiding principle of biology, I guarantee that you’ll see it almost everywhere you look.

Tagged , , ,

Science quote of the day

All sciences are connected; they lend each other material aid as parts of one great whole, each doing its own work, not for itself alone, but for the other parts; as the eye guides the body and the foot sustains it and leads it from place to place.

– Roger Bacon

This is one of the things that I love most about science: the interconnected nature of the enterprise, where every question leads you down another path of curiosity and lets you traipse through someone else’s backyard of knowledge. We can be too focused on our own domain sometimes, possibly as a defensive reaction to the massive flood of information coming at us from our own little corner of our own little subfield. But we must never forget that we are traversing a web, and that nothing we do makes sense without pulling back to see its entirety.

Tagged , ,

What I’m reading now…

I’ve been waiting for this book to come from Amazon for quite some time, but it’s finally here!

"Exploring animal social networks" cover image

Review to come when I’m done.

Tagged , ,

Computational behavioural ecology…?

An image of a man wearing a t-shirt that reads "Deep down inside, we all love math".

I know I do.

I’ve written about the methods that we use in behavioural ecology, and the method that I use the most is definitely modeling.  To be more precise, I do a lot of computer simulation work on the evolution of behaviour (my focus is on evolutionary algorithms and individual-based models).  I do some formal mathematical modeling as well, primarily in game theory, but the bulk of my research is computational.  I admit it:  I’m a computer geek, and I always have been.  I love writing software, I love tinkering with code and hardware, and my natural approach to biological questions has always been to throw processor cycles at them.

Which leaves me wondering: what do we call computational studies of behavioural ecology?

The obvious answer, computational biology, is – I think – wrong.  At least, as it is currently defined, computational biology seems to be heavily focused on questions at the level of the cell or below.  If you look at the Wikipedia entry on computational biology, you’ll see that the examples given are all about cells, molecular biology, genomics, and so on.  Bioinformatics, computational genomics, “computational biomodeling” (not sure what that is, to be honest), systems biology, etc. are all examples of labels under the heading of computational biology, and none of them apply to the kind of work I do.  It’s natural that a lot of attention would be focused on this level of inquiry – people doing exciting work in genomics, cell biology, and proteomics are drowning in data and need computers to help them climb out of the well.  But I spend my time at the level of the individual and the evolution of their behavior, which doesn’t give me a lot to talk about with the computational biology people.

At the other end of the scale is the relatively new field of computational ecology.  If you forced me to chose right now, I would probably throw in with this camp, but it’s still a bit of an uneasy fit.  Computational ecology focuses on global population-level questions, and big ecosystems with many layers of complexity.  This is a fascinating area of work, but just like behavioural ecology differs from classical ethology / ecology in focusing on the individual, so too does the work I do focus on the evolution of mechanisms and behaviour at the level of the individual.  A typical question that I’m working on right now is the evolution of learning mechanisms for social foraging – how do animals learn to use the best strategy when foraging in a group, and what is the form of the mechanisms which allow them to do that?

And in the end, I’m left wondering where I fit.  There are others like me, of course;  for example, I’ve always admired the work of Dr. Graeme Ruxton, as well as the Laland group, both of which have done work in the same vein (this is by no means an exhaustive list, of either the people whose work I admire or who do work in the same area).  With the increasing specialization of scientists into subfields of subfields of major fields, I’m hesitant to invent a new term for myself and others like me, but maybe it’s time.

So:  computational behavioural ecology, anyone?

(Photo credit: Network Osaka)
Tagged , , ,

How do we study behavioural ecology?

Yesterday, I wrote about my current field of study, behavioural ecology, attempting to explain what it is and what questions it tries to answer.  But I didn’t talk much about how it is studied.  How do we answer questions in behavioural ecology?

In general, there are three (overlapping) general techniques to be used.  Field studies are common, and have the flavour of the Wild West:  you pick your species, pack up your gear, and head into the wild blue yonder to collect data on your chosen animal.  You spend days, weeks, or months in the field, hoping that your data cooperate, and then come back to civilization to run some stats and publish your findings.  Field biology is romantic, and it draws a lot of outdoors types who like science and want to spend their time in the wilderness. I say this with a touch of envy;  I wish I had it in me to be a field biologist, but it just doesn’t work for me.

The second major method is the laboratory experiment.  Laboratory studies in behavioural ecology are important for their ability to control for confounding variables in a way you simply can’t in the wild, though this often comes at a corresponding cost to ecological validity (the match between the experimental setup and the real environment of the animal and its behaviour).  Labs tend to work on a few model species;  for example, one of the species that my lab does work with is the zebra finch (Taeniopygia guttata), which is one of the most widely-studied bird species.  Fish, like cichlids or guppies, are also common in lab work on behaviour.  Lab work is where you most often see the use of methods from other areas of biology, like molecular work or behavioural endocrinology, for obvious reasons of convenience.  I’ve done some lab work myself, but it is by no means where I spend the bulk of my time.

The third major method in the study of behaviour is modeling.  Biologists use mathematics, computer simulation, and statistics to create models of the behaviour and its evolution so that we can better understand it.  These models are used to drive new empirical work in the lab or the field, or explain results which have already been collected.  Because I’m primarily a modeler myself, you’ll see a lot about that on this blog, because one of the goals I have is to demystify the process and results of mathematical models of behaviour.

Now, I’ve talked about these three methods like they are distinct things, but it has to be stressed that everyone studying behavioural ecology has different mixtures of each tool in their tool box.  Some people are mainly field biologists, but even hardcore field people will do lab experiments to explore aspects of behaviour that they see in the wild in a more controlled experiment, and they will turn to models to help explain that behaviour.  Experimentalists love to see their work replicated in wild populations, and some will even head out into the field to do it themselves, while modelers have nothing to explain if there’s no data from experiments or field studies!  As a modeler myself, I never lose sight of the fact that the reason I’m trying to create these models of behaviour is to explain why real animals do the things that they do.

I know, I know;  this is a bit of a dry topic, reminiscent of the “methods” sections of your intro science courses in undergraduate studies.  But it gets better: in coming posts, I’m going to write about examples of each of these three methods from the best of both current and historical work, to showcase some of the more exciting examples of behavioural ecology past and present.  If you have any requests for topics to cover, or questions about how behavioural ecology is studied, please let me know by e-mail, Twitter, or leave a comment!

Tagged , ,

What is “Behavioural Ecology”?

The first and most obvious question to answer with this blog is what “behavioural ecology” (or “behavioral” ecology, for my American counterparts) is all about.  Historically, there has been some confusion on this matter, because of the overlap between various areas of study which deal with the question of animal behaviour. But I’m getting ahead of myself.

What is behavioural ecology?  In the introduction to an important textbook in the field, “An introduction to behavioural ecology“, John Krebs and Nick Davies write:

This book is about the survival value of behaviour. We call this subject “behavioural ecology” because the way in which behaviour contributes to survival and reproduction depends on ecology.  If, for example, we want to answer the question “How does living in a group contribute to an individual’s survival”‘, we have to start thinking in terms of the animal’s ecology; the kind of food it easts, its enemies, its nesting requirements and so on. These ecological pressures will determine whether grouping is favoured or penalized by selection. Behavioural ecology is not only concerned with the animal’s struggle to survive by exploiting resources and avoiding predators, but also with how behaviour contributes to reproductive success (p. 1).

The quote above shows that behavioural ecology is defined by the fields that intersect it.  These fields include ecology / ethology, evolutionary theory, and comparative psychology.  But the overriding focus of behavioural ecology is the study of behaviour through the lens of evolution, a laser focus that has set it apart from other fields in the past.  Behavioural ecology includes optimality theory and game theory (including evolutionary game theory) as part of its theoretical traditions, driven by the work of giants like William Hamilton and John Maynard Smith.  The kinds of questions that behavioural ecologists study include:

  • Information use by animals.  How do animals gather information about their environment, either personally or by observing others, and then use that information to improve their chances of survival or reproduction?
  • Behavioural syndromes / animal personality.  What drives the consistent differences in individual behaviour that we see in animals (like “aggressive” or “exploratory” behaviour) across different contexts?
  • Life history strategies – body size trade-offs, reproductive timing, etc.
  • Questions about foraging, whether as solitary foragers (optimal foraging theory) or foraging in groups (social foraging theory).  This is an area dear to my heart, because questions about social foraging are occupying the majority of my Ph.D.
  • The evolution of behaviour for mating and breeding;  mate selection, breeding habitats, and so on.
  • As above, the benefits and costs of group membership.  When should an animal join a group, and why?
  • The evolution of other social traits.
  • Learning mechanisms which drive animal behaviour.

And the list goes on.  The questions above come from a quick scan of chapter titles in a recent text on behavioural ecology (Behavioural Ecology, by Danchin, Giraldeau, and Cézilly), but that is not an exhaustive list by any means.

However, in our hurry to set ourselves apart from other fields, I hope that we don’t lose sight of what we owe them and what we can offer them.  I view behavioural ecologists as occupying a unique vantage point smack in the middle of those fields of study which occupy themselves with animal behaviour, working to both integrate the knowledge from those around them in an interdisciplinary way as well as extending that knowledge to give back.

But hey, I’m just a hopeless romantic.

Tagged ,