Time itself as a resource that drives evolution

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Many of the key revolutions, or at least, overhauls, in biological thinking have come as a result of the broad realization that a thentofore identified variable is not simply background, but central and causative.

I’m sure everyone always thought, since first recognized, that if genes are important than good genes would be good. Great, even. But it took a while for Amotz Zahavi and some others to insert good genes into Darwin’s sexual selection as the cause of sometimes wild elaboration of traits, not a female aesthetic or mere runaway selection.

I’m sure wildlife biologists and others who observed whole organisms, not to mention human psychologists and anthropologists, noted the importance of the efforts parents put (or failed to put) into their offspring’s well being. But it was not until Robert Trivers pointed it out in 1972 that we realized that so much of behavioral biology is powerfully explained by organisms competing to acquire, control, direct, or interfere with this critically important resource: parental investment.

Time has always been part of the context in which ecological interactions happen, it is often the very x-axis in a graphical display of relevant variables, or the first (or second) column in a data collection form while observing life in the wild. But Eric Post argues that time is itself a resource competed for and used by organisms. It is, after all, impossible to grow, maintain, or reproduce across zero time, and the relative distribution of energy across these three pillars of life history is measured not as the amount of energy expended, but the proportion of available energy expended over a period of time, and a key variable is often not how much but when.

Organisms, as individuals but with effects that manifest at the species and co-evolutionary levels, barter in time. One of the most interesting mysteries of ecology can be understood in these terms. In places such as at my house in Minnesota there is one species of hummingbird. The hummingbirds arrive seasonally in time to take advantage of emerging nectar sources, stay around to exploit these resources as they emerge and run out through the summer and early fall, then vamoose in time to fly to the tropics as those resources are running out, sipping themselves all the way south.

But in the South American tropical rain forests, there are many species of hummingbird, some migratory but many not. There, rather than the hummingbirds timing their behavior to match the background of nectar rich sources, the nectar sources themselves behave to facility the survival of the hoards of hummingbirds humming around looking for food. It makes sense for certain kinds of trees (broken into functional groups mainly by their mode of seed production and dispersal) to flower and then fruit on a schedule matching mainly rainfall or seasonal pollinators. But those that are pollinated by non-seasonal hummingbirds have among them early flower producers and late flower producers, to the extent that as a group of species, they produce nectar bearing flowers all year round so the local hummingbirds have something to eat. Each tree species seems to be going out of its way (in time) to keep the hummingbirds alive for the next tree species up for flowering, ultimately, of course, so that those hummingbirds are alive next year! How does straight forward Darwininan thinking, or even the usual co-evolutionary conceptions of species interactions, explain how this system developed? Time is a critical co-variable with nectar production that needs to be differentiated across the year, and somehow this is managed across genera of flowering tree. To explain how that works, to even think about how that works, one needs a good theory of time in ecology.

Between how time is divided up across life history parameters (noted above: growth, maintenance, and reproduction), and how time is competed for across species in co-evolutionary syndromes, there is a lot to think about. Eric Post, in Time in Ecology: A Theoretical Framework, gives us an excellent framework for that thinking. In this book, Post puts time in perspective as a resource that drives natural selection, limits species, and helps determine the overall pattern of co-evolution and evolutionary change we observe in living systems.

Time is also important when things change (over time), and Post addresses this as well, including in reference to climate change.

(Note that Post is also the author of Ecology of Climate Change: The Importance of Biotic Interactions and Wildlife Conservation in a Changing Climate.)

This is a technical monograph, though well written and quit accessible. It will change how scientists think about certain problems, and it will serve as a textbook in graduate level or advanced undergraduate seminars or classes in ecology.

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3 thoughts on “Time itself as a resource that drives evolution

  1. Eric is a fantastic ecologist and I was delighted that he was a co-author on our Bioscience paper on polar bears and climate change in the blogosphere. I will most definitely buy a copy of this book.

  2. Typos: “… to facility the survival of the hoards of hummingbirds …” should be “… to facilitate the survival of the hordes of hummingbirds …”

  3. Robert Trivers pointed it out in 1972 that we realized that so much of behavioral biology is powerfully explained by organisms competing to acquire, control, direct, or interfere with this critically important resource: parental investment.

    Richard Dawkins was fond of citing Robert Trivers who contributed a Forward to the first edition of ‘The Selfish Gene’, which I once owned it being ‘borrowed’ by my children and then went around their friends. The same fate befell subsequent editions over time, I now have the ’30th Anniversary Edition’ which once again contains that forward by the remarkable Trivers.

    Robert Trivers crops up in a number of Dawkins’ books including ‘Climbing Mount Improbable’ my favourite but it is a tough call but it wins for the absorbing chapter ‘A Garden Inclosed’ one has to be absolutely alert and concentrating to follow the twists in a fascinating story of wasps and figs.

    Dawkins has much to say in his books about not only parental involvement but the involvement of other close kin, siblings of the parents.

    In Dawkins’ ‘Brief Candle in the Dark: More Reflections on a Life in Science’ (recommended reading BTW along with ‘An Appetite for Wonder’) we find this passage pages 337-338 paperback:

    I’m grateful to that inspired pioneer Robert Trivers for calling my attention to a fascinating paper by Paul and Holly Ewald on a Darwinian approach to cancer which makes use of the idea of the extended phenotype. It is well understood that the cells within a tumour are subject to natural selection within the tumour. But it’s time-limited rather than open-ended natural selection: mutant cells that become ‘better’ (better at being cancerous, emphatically not better for the patient) outcompete less malignant cells within the tumour, becoming more numerous in the tumour. But that evolutionary process terminates with the death of the patient. And there exists a parallel, but more long-term (because transgenerational) selection of genes in the rest of the body, to resist cancers, erect barriers against them, develop immunological tricks against them and so on. It’s an asymmetric arms race, because the anti- cancer tricks have been honed against cancers of many past generations. The tricks of the tumours themselves have to be evolved afresh in each generation, for they begin their malign evolution anew in each body, starting as normal, healthy cells which then are naturally selected to evolve, step by step, the qualities needed to outcompete other cancer cells in the race to multiply.



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