How fast do ecosystems recover from disturbance? It’s complicated.

ResearchBlogging.orgIn the 21st century, human activity promises to impact the natural world on an unprecedented scale. In order to decide where to focus conservation effort, one thing we need to know is how permanent the damage from a forest clear-cut or a collapsed fishery actually is. A paper in this week’s PLoS ONE looks at natural systems’ ability to recover after human and natural disturbances, and the authors say the results are hopeful. I’m not so sure.


A clearcut.
Photo by : Damien.

The authors, Jones and Schmitz, assemble a meta-dataset of ecological studies published from 1910 to 2008, all examining the recovery of either ecosytem functions (like total nutrient cycling rates) or plant or animal diversity following disturbances as diverse as hurricanes and oil spills. They then calculated the proportion of measured variables that recovered, or failed to, within the period studied by each paper in the dataset, how much the measured variables had been altered by the disturbance, and how long it took before they returned to their pre-disturbance state.

The results are complicated, to say the least. For example, here’s Figure 2, which charts the times to recovery for variables measuring animal community recovery (black bars), ecosystem function (white bars) or plant community (gray bars), broken down by ecosystem type in the top panel, and by disturbance type in the bottom panel:

The authors’ conclusion? There is “no discernable pattern.” Which I can’t really dispute — recovery times look highly idiosyncratic. An ANOVA performed on the data finds significant effects of ecosystem type and disturbance type, but what does that tell us? Different ecosystems recover differently. Forests take the longest to recover, which makes sense given that trees grow slowly, and succession from clearcut to mature forest can take centuries. Similarly, ecosystems experiencing multiple types of disturbance took the longest to recover.

Of the ecosystems that do recover, the authors point out, recovery occurs comparatively rapidly:

Among studies reporting recovery for any variable, the average recovery time was at most 42 years (for forest ecosystems) and typically much less (on the order of 10 years) when recovery was examined by ecosystem. When examined by perturbation type, the average recovery time was no more than 56 years (for systems undergoing multiple interacting perturbations) and typically was 20 years or less …

The authors then perform a regression of the strength of disturbance (i.e., how much the measured variables changed due to disturbance) against the time needed for recovery. The data set is necessarily small, because not many studies follow an ecosystem all the way from disturbance to complete recovery, and they find a significant effect of disturbance strength on recovery time mostly because of a single data point.

Jones and Schmitz conclude from this dataset that ecosystem recovery from human disturbance is frequently possible within human lifetimes, especially if we put in the effort for restoration. I’ll buy that; but I think the more important lesson to draw from this paper is that, after a century of watching the natural world respond to human activity, we still can’t predict what the results of our actions will be. It shouldn’t need saying, but when we fiddle with our life-support systems, we must proceed cautiously.

Reference

Jones, H., & Schmitz, O. (2009). Rapid recovery of damaged ecosystems PLoS ONE, 4 (5) DOI: 10.1371/journal.pone.0005653

Oh, hey

So I just noticed that this was my 50th post through the Research Blogging content aggregator. I joined Research Blogging last July, and it’s been nothing but good for traffic to D&T — and maybe more importantly it’s one of the first places I check when I want to see what other scientists are blogging about.

I’ve now tagged every piece submitted through the system, and will continue to do so for organizational convenience. It’s variable output, quality-wise, but pretty representative of my free-time science reading, which is what I aim for my scientific blogging to be.

In social courtship, it pays to be a good wingman

ResearchBlogging.orgThe search for a mate is traditionally a selfish enterprise. After all, the ultimate goal is reproduction, and — barring any effect of kin selection — natural selection only cares about how many babies you make, not how many you help to make. This is fundamentally a biological question, though, and if there’s a universal rule in biology, it’s that nature is good at making exceptions.

One such exception is the wire-tailed manakin. A study in the latest Proceedings of the Royal Society seems to show that male manakins can boost their own mating success by helping other males attract mates [$-a]. Manakins are a family of brightly-colored neotropical birds, and the males of many manakin species attract females by putting on dancing displays, as seen in this video:

(I seem to recall that there’s also some excellent footage of manakin dancing in David Attenborough’s The Life of Birds.)

To dance for females, male manakins gather at locations called “leks,” where most try to establish a small territory to perform. Among wire-tailed manakins, though, some males will team up to dance — presumably because if one brightly-colored male jumping around on a branch is attention-grabbing, two or three are even more so. But in these “coordinated displays,” one performer, the socially dominant one, is most likely to mate with the females who like the performance. So what’s in it for the other guys?

There seem to be two possible (though not mutually exclusive) explanations [$-a]: (1) that the mate-attracting dancing does double duty to establish social dominance relationships among males, and (2) that, even if it wins fewer mates than the “lead” role, being a supporting player in a successful cooperative display means better mating prospects than trying to go it alone. To try and disentangle these two possibilities, the new study’s authors followed the behavior of wire-tailed manakins at several leks for four years, building a “social network” of male-male cooperation at the leks and counting the offspring each male bird by taking DNA fingerprints of the males and of newly-hatched chicks in the nests of females who attended each lek.

Although the most reproductively successful males at each lek were all territorial, defending their own spot at the lek and dominating other males who joined in the display on that territory, non-territorial “floater” males tended to make more babies if they joined in more displays. In fact, the number of offspring produced was best predicted by the number of cooperative display interactions in which a male joined, whether he had his own territory or not. This complements an earlier study by the same group [$-a], which showed that a male’s “tenure” — how long he had been dominant in a territory within a lek — was the best predictor of mating success, but that a male’s rise through the social hierarchy at a lek was facilitated by cooperative interactions with other males.

In short, male manakins seem to help each other in mating displays for essentially selfish reasons. Being a supporting dancer has a coattail effect, earning more mates than trying to go solo, and it helps young males improve their social status toward the day when they can establish their own display territory.

References

Prum, R.O. (1994). Phylogenetic analysis of the evolution of alternative social behavior in the manakins (Aves: Pipridae). Evolution, 48, 1657-75 DOI: http://www.jstor.org/stable/2410255

Ryder, T., McDonald, D., Blake, J., Parker, P., & Loiselle, B. (2008). Social networks in the lek-mating wire-tailed manakin (Pipra filicauda) Proc.R. Soc. B, 275 (1641), 1367-74 DOI: 10.1098/rspb.2008.0205

Ryder, T., Parker, P., Blake, J., & Loiselle, B. (2009). It takes two to tango: reproductive skew and social correlates of male mating success in a lek-breeding bird Proc. R. Soc. B, 276 (1666), 2377-84 DOI: 10.1098/rspb.2009.0208

Adulthood

By age 25, it’s time to grow up.

19. Take care of yourself. If you are sick, visit a doctor. If you are sad, visit a shrink or talk to a friend. If you are unhappy in love, break up. If you are fed up with how you look, buy a new shirt or stop eating cheese. If you have a problem, try to fix it. Many problems are knotty and need a lot of talking through, or time to resolve, but after a few months of all complaining and no fixing, those around you will begin to wonder if you don’t enjoy the problems for the attention they bring you. Venting is fine; inertia coupled with pouting is not. Bored? Read a magazine. Mad at someone? Say so — to them. Change is hard; that’s too bad. Effort counts. Make one. Your mommy’s shift is over.

The whole list is well worth reading; it crystallizes a lot of what I sort of generally sensed about the difference between me and the undergrads, when I arrived on campus to start work on the ol’ Ph.D. Via kottke.

Excuses, excuses

Via the Slate Gabfest on Facebook: a great long profile of Andrew Sullivan. I started reading the Daily Dish regularly during the presidential campaign last fall, and I still check it multiple times a week; I can identify with Sullivan’s attempts to reconcile his (apparent) internal contradictions. What struck me, though, was the piece’s account of what you might call Sullivan’s “neoconservative period,” his reaction to the attacks of 11 September, 2001:

“I experienced 9/11 very personally,” he says. “The jihadists attacked my dream, my place—I felt like I had been beaten or raped. I succumbed to the fear a lot of us felt—panic really—about this country being in mortal danger. And neoconservatism seemed like the only ideology on the shelf with a plan for how to react immediately, and I turned to it.”

Having voted for George Bush in 2000, he now became one of his most militant supporters, urging him to invade not just Afghanistan but Iraq, in charged and extreme language. His blog posts from that time are quite startling to read now—more expressions of rage and grief than political analysis.

Sullivan is hardly the only person in American politics who reacted like this. (I recall just about falling out of my chair when a commentator on NPR proposed that a nuclear strike would be a good response to the destruction of the World Trade Center.) And Sullivan has clearly come to his senses and now strongly repudiates the positions he took during that period.

But all that said, I’m tired of this narrative about post-9/11 panic. It feels like excuse-making, and it implies that the near-immediate search for a retaliatory target and the fearmongering push for the invasion of Iraq were natural, understandable responses to the attacks on the WTC and the Pentagon. You know what? They weren’t. Panic and fear and anger may be natural, but acting on them is stupid. If we haven’t learned that lesson from the Bush Administration, then we’ll almost certainly repeat the same mistakes in the aftermath of the next terrorist attack on U.S. soil. And I’ll be frank — the prospect of re-making those mistakes scares me more than whatever that attack may turn out to be.

Evolution 2009: How best to go social?

Evolution 2009The Evolution 2009 meetings are less than a month away. Now is probably the last chance to assess what online presence and utilities the meetings will have.

Right now, we have the meeting website, with a page for bloggy stuff — and it’s kind of a mess at the moment, with my hastily scribbled explanation about the power of TEH INTERNETS and a list of the handful of science blogs (this one included) that are displaying an Evolution2009 badge and will have a contributor at the meetings. We’ve also got the Evolution2009 Twitter feed. What more could be done with this space, both to improve the meetings for participants and to open them out to the public? I have two ideas:

  • A blog carnival. I’ve participated in several blog carnivals in the last few months, including the Carnival of Evolution and Berry-go-Round. The Blog Carnival utility seems like a good way to round up posts on a given topic, and posting submissions to the existing “blogging” page seems like a logical way to show what participating bloggers are writing about the meetings.
  • A FriendFeed group. Following the approach used at 2008 meeting of the International Society for Computational Biology, we can open an aggregate feed of twittering, blog posts, and other online reactions to the meeting. In fact, I’ve set it up here already. I have two questions/qualms about this:
    • (1) Should such a group be open or invitation only? Maybe I’m paranoid, but I do worry about hijacking by, e.g., creationists.
    • (2) More importantly, how many people would actually contribute? The ISCB had “a core group of ten contributors” out of 1600 attendees. The Twitter feed has, as of the time of writing, 68 followers, not all of whom are individuals, and many of whom are not active users of Twitter, but rather seemed to have subscribed just to get the latest news. (Which is fine! If that’s all the feed achieves, it’s been useful.) So how many folks would actually Twitter during the meetings?

Anyway, I’m going to put the word out over the Twitter feed — I’d love input on both of the above points, as well as suggestions for other utilities or approaches.

When the going gets tough, C. elegans gets sexy

ResearchBlogging.orgThe trouble with sex, from an evolutionary perspective, is that it’s expensive. Not just in terms of the efforts a sexually-reproducing organism has to go through to secure a mate; every offspring produced by sexual reproduction bears half the genome of each of its parents, compared to an asexual offspring, which bears a complete copy of its only parent’s genome. So, in terms of natural selection, an asexual critter gains twice as much reproductive fitness for each offspring it produces — asexual critters should overrun sexual competitors.


C. elegans tagged with gfp.
Photo by derPlau.

And yet they don’t. Sex is widespread in the animal kingdom, and common in the plant kingdom (although many plants can switch between sexual and asexual reproductive strategies). Many explanations have been proposed for this quandary; most of them have to do with the idea that sometimes it’s useful to mix your genome with someone else’s. The current front-runner hypothesis is that sex basically helps to separate useful genes from damaging ones [PDF], making sexual offspring more fit, on average. A different (but not mutually exclusive) possibility is that by mixing up genomes, sex can help generate the genetic variation necessary for a population to evolve in response to environmental stress. This might explain a discovery reported in this month’s issue of Evolution: that stressful conditions trigger the normally hermaphroditic nematode Caenorhabditis elegans to begin reproducing sexually [$-a].

The study’s authors subjected three experimental lineages of C. elegans to stress — starvation — triggering the worms to produce semi-dormant larvae called “dauer.” They then relieved the stress by transferring the population to a new food source. Some experimental treatments were kept well-fed after one period of dauer; others were repeatedly starved. Two of the three experimental lines responded to repeated episodes of dauer by producing male offspring instead of hermaphrodites.

Some of this effect was due to males’ better ability to survive dauer state than hermaphrodites. A large portion was because hermaphrodites became more likely to mate with males (with a possibility to produce male offspring) following dauer, though. This kind of facultative sex takes the best of asexual and sexual reproduction — the twofold fitness benefit of asexual reproduction most of the time; and the improved response to natural selection associated with sex in stressful conditions, when it’s needed most.

References

Keightley, P., & Otto, S. (2006). Interference among deleterious mutations favours sex and recombination in finite populations Nature, 443 (7107), 89-92 DOI: 10.1038/nature05049

Morran, L., Cappy, B., Anderson, J., & Phillips, P. (2009). Sexual partners for the stressed: Facultative outcrossing in the self-fertilizing nematode Caenohabditis elegans.
Evolution, 63 (6), 1473-82 DOI: 10.1111/j.1558-5646.2009.00652.x

Mennonites in pink

Pink Menno Campaign is organizing people to support broader (and officially-sanctioned) inclusion of LGBTQ people in the Mennonite Church by wearing pink at the upcoming biennial convention of Mennonite Church USA.

Mennonites are in a slightly unusual position w/r/t sexual orientation — the Confession of Faith in a Mennonite Perspective accepts only heterosexual marriage — but the CoF is more a descriptive than a prescriptive document, and because MCUSA lacks some sort of centralized doctrinal enforcement, a few individual congregations do welcome LGBTQ folks and even perform same-sex marriage ceremonies. Sometimes such congregations and/or their pastors are “disciplined” in various ways by the local-level church authorities that can do such things, and the results are never happy.

I thought it was a big deal when, as a delegate at the last MCUSA conference, I was involved in preparing a statement on behalf of young Mennos that included a very brief nod to broader inclusion; much more recently, a group of Mennonite pastors signed an open letter to the church calling for an end to the exclusion of LGBTQ folks. (An article in Mennonite Weekly Review covers both the letter and its context.) Progress? Hard to say. A Delegate Assembly full of pink t-shirts is a mighty appealing image, though.