ESA – from our California Correspondents

The American ecological society has just finished its annual meeting in Sacramento, California, and the BES was well represented.  For those of you who missed it, let me summarize my impressions.

Sacramento has a gleaming modern core, surrounded by genteel Victorian suburbs, surrounded by millions of acres of dry billiard-table flat agricultural land.  The population shows a typically Californian ethnic diversity, with every Pacific-rim culture well represented.  When you interact with them, however, they all seem to speak the same relaxed Californian version of English (anyone with a foreign accent is likely to be from the meeting).  The modern city exudes environmental consciousness: Every street is lined with large shade trees; street design encourages safe driving; a light rail system whisks you efficiently around town; police ride bicycles not cars; and all fountains have been turned off to conserve water in the draught.

The meeting was BIG, with ca. 3500 attendees (organizers tell me this is actually a small meeting compared with previous years).  People streamed in and out of the Convention Center and nearby hotels like an underground station at rush hour.  Graduate students were strongly represented (two of my own students presented).  By my unsystematic reckoning, the age distribution was bimodal with a large peak at ca. 28 years and a smaller one at ca. 58.  Both genders seemed equally represented.  I was constantly avoiding baby buggies.  Is a meeting dominated by graduate students and young parents a good thing?  Yes!  Notwithstanding a degree of hubris and naiveté, the standard of presentations seemed quite high.  I come away with a strong impression of youthful energy and enthusiasm.

With more than 300 thematic sessions, scheduling your time becomes a serious dilemma.  Hallways, foyers, and lounges were lined with people closely studying their printed programs and mapping out their day.  Should one politely settle in a single session and hear out all the talks on a particular topic, or should one rush from session to session to catch particularly attractive individual talks?  I began the week resolved to devote my whole gracious and dignified attention to entire sessions, but soon began scooting in and out as individual talks varied so widely.  At least in the sessions I attended, talks did not fit the themes closely, e.g. a talk on dynamic landscape models followed one on transitions between physiological dormancy states – both aspects of biological invasion (one of which I presented).  One can’t fault the organizers for the weak transitions, however.  Considering the number and variety of submissions, it’s a wonder that sessions were as unified as they were!

Enough social observation – what direction of ecological science was revealed at the meeting?  A tally of oral and poster sessions gives a crude idea of direction.  Among 300+ sessions (ca. 8 contributions per session), the winner was clearly Climate Change, appearing in the title of 33 sessions.  Invasion (16 sessions) and Disturbance Responses (13) were also popular topics.  The ecology of disease (8 sessions) and urban ecosystems (7 ) look like rising stars.  And there were many curious one-off sessions, including “interaction with religion” and “skin microflora”.  My choice for the animal- and plant-of-the-meeting awards would be white-tailed deer (Odocoileus virginianus) and Japanese stilt grass (Microstegium vimineum), respectively.  Both are serious management concerns in the eastern United States, and both appeared in many talks.

A large number of presentations used GIS to generalize local observations to entire landscapes and regions for management purposes (frequently tied to climate change).  Conversely, many population-level studies used deterministic projection methods to extrapolate local behavior over large areas and long time frames (the authors would do well to consult the literature on landscape heterogeneity).  The terms “local” and “spatial” were particularly slippery, applied at every scale from the neighborhood of an individual plant to sections of entire continents.  One of the most important benefits I derive from these meetings is acquaintance with new methods. The trendy new statistical method is clearly “Integral Projection Modeling” with “Maximum Entropy Modeling” in a close second place.  Bayesian methods, zero-inflated regression, and PERMANOVA (previous favorites) have become rather ordinary.  I now have a list which will guide my bed-time reading for several months at least!

Is a mega-meeting such as this one really worth the effort or would we be better served by smaller, more focused meetings?  Although I enjoyed connecting with old friends, and serendipity revealed some fascinating new ideas, the enormity of the meeting caused me to miss many interesting discussions and somehow impeded personal interaction.  For the moment, however, I set the question aside.  I need to write follow-up emails to the many new friends I met in Sacramento!

Best regards,

The California Correspondent

Glenn Matlack

Associate Editor, Journal of Ecology

***

From plant-soil feedbacks to rhizosphere ecology to soil community diversity and aboveground interactions, the talks I attended at ESA 2014 indicate that a great deal of interest exists concerning the black box that is the soil.  Without a doubt we need a better understanding of the mechanisms by which the soil microbial communities influence aboveground plant and community dynamics.  To say that aboveground plant communities are an epiphenomenon of belowground processes is not an exaggeration and ecologists often are guilty of ascribing causation to aboveground treatments without an understanding of how plant responses to those treatments are mediated by interactions belowground.  Invasive species ecology is one of those areas where our ability to understand spread is hampered by our lack of knowledge of interactions between non-native plant species and belowground biota.  In particular, new studies are emphasizing the importance of genotype interactions, changes in the intensity of pathogen loads over time, the potential advantages of intraspecific competition over interspecific competition, and even that the invasive characters of some species may be emergent properties in the invaded range.  Needless to say, experiments that take into account a greater number of the growing list of potentially importance variables are few and difficult at the very least, but some very good work is being done nonetheless.

Andy Dyer

Associate Editor, Journal of Ecology

 

California, Here I Come!

OK—that’s corny, I realize.  Right out of the DeSylva/Meyer song of the same name from the 1921 Broadway musical Bombo, starring Al Jolson.  But it’s always uttered with a great deal of excitement by anyone who uses that expression, and this is no exception.  Annual meetings of the Ecological Society of America are always exciting for me, and even more so for this ‘easterner’ to be travelling to Sacramento.

As I shared in a similar blog for last year’s meeting in Minneapolis, MN, I have had a long-standing tradition of attending ESA meetings.  Among the historic high points are the symposia I organized and presided over (1993, 1998, and 2003) and serving as Program Chair for the 2010 meeting in Pittsburgh.  Because of my Chair-related, inside knowledge of symposia I was pleased to be able to connect with Journal editors, leading to a Special Issue in May 2011:  Ecological Consequences of Climate Extremes.

Furthermore, especially since my arrival in 1990 here at Marshall University—a public school small state (among the 50 United States, West Virginia ranks 38th in population) and with very limited personal access to colleagues doing similar research—annual ESA meetings have become a professional ‘lifeline,’ connecting me with ecologists from throughout North America and the world.  I also greatly enjoy both the talks and the feedback on current research I present every year.  But another extremely enjoyable tradition since joining the editorial board of the Journal of Ecology, is the annual dinner for editors—what an amazing combination of great food, wine, spirits, along with the best company and conversation.  Also from a personal standpoint, these meetings are special opportunities to combine keeping up on current research and seeing my ‘ESA friends,’ those folks I have met through the years who I would otherwise essentially never see.

So, what about this year’s ESA meeting in Sacramento, California?  Per usual, I will be excited to reconnect with those ESA friends, go to interesting talks, and re-join staff and fellow editors at Journal of Ecology for another great evening out for our annual dinner.  One special facet this year, however, will be the promotion by Oxford University Press of the publication of my third book, The Herbaceous Layer in Forests of Eastern North America, 2nd edition, the first edition of which actually began as an ESA symposium in 1998 in Baltimore, Maryland.

Finally, as is always my practice, I will present a paper.  This one examines a serious environmental threat—the effects of excess nitrogen (N) on forest biodiversity—by comparing results of field studies that look at the response of the herbaceous layer to experimental N additions in hardwood forests of sharply contrasting sites:  a temperate forest in West Virginia, and a tropical forest in southeastern China.  (COS 142-9 “Response of the herbaceous layer of contrasting forest ecosystems to excess nitrogen deposition”)

California, here I come, indeed!

Frank Gilliam

Associate Editor, Journal of Ecology

ESA by @ibartomeus

It’s always exciting to prepare for ESA. Here are some recommendations for people interested in biodiversity, global change, pollination, networks and more.

As you can see, my interests tend to be wide and hence I tended to run a lot amongst sessions in previous years. My plan this year is to run less and attend full sessions, and let talks within those sessions surprise me. A couple of symposiums looks really cool, like the plants and climate change with Camille Parmesan as moderator.

I was also positively surprised by the Ignite talks last year and the one on theory versus empiricism looks promising. If you are into reconciling theory and reality (I am) the talk by Simon Levin and the symposium on theory and conservation biology are a must. One big recommendation if you don’t yet know the ROpenSci people is one of his workshops to learn not only about a cool R package to retrieve species occurrence data, but about reproducibility and open science in general.

For those interested in pollination there is plenty this year. I plan to learn more about citizen science at the symposium on the great sunflower project and there is the usual Polination I and II sessions. This year I’ll present a pretty cool, but specialized talk about bee tongue lengths, but the work I am really exited about and I think will be of general interest is presented by James Reilly. He will present ongoing work where we show that number of species (e.g. pollinators) needed to fulfil a given ecosystem function increases as you increase the scale of inference. I believe its very interesting not only for pollinator, but for BEF people.

As opposed to the pollination talks, mutualistic network talks are very scattered among the sessions, but there are quite a lot of them in different sessions and, unfortunately, several overlaps in time. A good place to start is the Species Interactions III. Lastly what I really expect of ESA is to talk with a lot of people, specially new people, so if you want to chat with me about anything, you can find me @ibartomeus.

Ignasi Bartomeus

Associate Editor, Journal of Ecology

Football, plant demography & team science

This week lots of members of the Journal of Ecology Editorial Board are at ESA in Sacramento. See Executive Editor, David Gibson’s, earlier blog post about what he will be getting up to here. Don’t forget to visit the British Ecological Society’s stand either!

A few members of the Editorial Board have written about their schedules for the meeting. We are kicking off today with what’s on, Associate Editor, Yvonne Buckley’s agenda.

FOOTBALL, PLANT DEMOGRAPHY & TEAM SCIENCE

So I’m on the plane from Dublin to Chicago, the 1st leg of my trip to ESA & it’s the perfect time to plan my schedule. I’m loving the conference scheduling app but it doesn’t make it any easier to choose what talks to see and events to go to – how do I choose between “Pretty darn good control”, “Life history theory” & “Plant defences” on Tuesday afternoon or between “theory for conservation” and “ecological statistics” on Wednesday morning? It’s enough to drive one back to the drinks cart. More than likely chance meetings in the corridors will mess up my schedule anyway, but that’s what conferences are for, right?

I haven’t made it to ESA for around 5 years, since safe-guarding my evolutionary fitness curtailed my travels, so I’m probably most looking forward to meeting old friends & colleagues from Australia, the UK & USA and catching up on what’s new. Fitting nicely with this theme I’ve organised an Ignite session on spatial plant population dynamics on Thursday at 3:30pm (rm 313) which cunningly enables me to meet up with old friends & gives me an excuse to meet some movers & shakers in spatial dynamics. My husband once told me that Bolton’s best 100 goals was a great video “even if you don’t like football”, he was right, and in the same vein I can assure you this will be a cracking session even if you think you aren’t into plant demography ;-).

I’ll be furiously scribbling notes at “The science of team science” special session at 10:15 on Monday as I’ll be launching a new coordinated observational network, PLANTPOPNET at ESA. Find out all about it on Thursday or stop me in the corridor so I don’t have to make agonising session choices.

Yvonne Buckley

Associate Editor, Journal of Ecology

Journal of Ecology representation at the ESA Annual Smorgasbord

It’s that time of the year again when ecologists from around the globe descend upon a convention center in North America for a week-long frenzy of eco-geeking.  I missed last year’s bash in Minneapolis because I chose to wait a couple of weeks and attend the British Ecological Society’s Centenary celebration in London (see why here).  But, I’m excited to be getting back to my annual ecological fix with the ESA, this year in Sacramento, Ca.

If you’ve never been to an ESA Annual Meeting before, be prepared to be overwhelmed with choices of talks to listen to, posters to see, mixers to attend, and people to meet. Playing “spot the sandals, shorts, or beard” is no contest with this crowd. If you are new to this meeting then start by attending the “How to Get the Most out of ESA’s 2014 Annual Meeting: An Orientation for Student Attendees” on Monday morning.

There’s a lot to look forward to. Here are a few things that caught my eye looking briefly over the program. Kathy Cottingham’s plenary talk on “Wearing an ecologists’ hat and facing a world of change”,  looks like a great way to kick off the week on Monday morning. After that it’s anyone’s guess where I’ll end up. I’ll definitely stop into some of the symposia. Tentatively, I’d like to listen to some of the “Extreme Climate Events…” symposium on Tuesday afternoon, “Plants and Climate Change…” on Wednesday, and “Managing Biotic Resilience…” on Thursday. Journal of Ecology is publishing a Special Feature on “Forest Resilience, Tipping Points and Global Change Processes” early in the New Year and I’m interested to learn more on this important topic. And, that’s just symposia that caught my eye, I won’t even try here to worry yet about the 20 Special Sessions,  52 Organized Oral Sessions, and 143 Contributed Talk Sessions. Of these however, I do like the look of the Organized Oral Session “Ecological Genomics as an Emerging Field…” on Tuesday morning. Overwhelmed yet? But, I do know that I’ll be at and around Poster 33-42 on 4:30 – 6:30 on Wednesday. Stop by if you are interested in “Effect of Dominant Species on Community Phylogenetic Structure in a Grassland Restoration”.  Just be sure to direct the difficult questions for my doctoral student Mohammad Khalil!

When I do get overwhelmed (usually by Tuesday afternoon), I head for the Exhibit Hall to check out the stands and posters. Come along and find some BES “important people” (BES Executive Editor @HazelNorman, JEcol Managing Editor @BaierAndrea) and journal Editors (including @amyt austin and me from Journal of Ecology).  We would love to talk with you about plans you might have for sending your best work for potential publication in one of the BES’s five journals.

Enjoy the meeting, and follow me as I’ll be live tweeting @DavidJohnGibson

David Gibson
Executive Editor

Executive Editor’s Forward to ‘Ecology in China’ Virtual Issue

The Editors of Journal of Ecology are pleased and excited to present eight papers as part of the BES’ ‘Ecology in China’ Virtual Issue. Papers from each of the five BES journals are represented in this Virtual Issue (See MEE’s blog post). These papers are a sample of the increasingly sophisticated and ground breaking ecological work that is being conducted in China. The majority of these papers reflect collaborative work between Chinese scientists and Western colleagues, and it is clear that all participants benefit in such partnerships. It is also clear from just these papers that ecological work in China covers a wide range of ecological topics. The Journal of Ecology papers in this Virtual Issue cover topics ranging from population through ecosystem ecology, above- and belowground systems, interactions with fungi and animals, and address theoretical, empirical, and applied concepts. There is no question that these studies are pushing forward the discipline. For example, Liu et al.’s paper “Understanding the ecosystem implications of the angiosperm rise to dominance: leaf litter decomposability among magnoliids and other basal angiosperms” is also part of the Journal’s Special Feature “The Tree of Life in Ecosystems” that is setting the research agenda for understanding eco-evolutionary relationships between plant species and ecosystem functions. Indeed, stay tuned for an Eco-Evo Special Issue in the Journal early next year! The other papers in this Virtual Issue are similarly exciting and important. We look forward to extending this growing relationship with our Chinese colleagues and seeing more of their best work in Journal of Ecology.

David Gibson

Executive Editor

Life-history costs and sprouting by Richard Shefferson

For almost 100 years plant ecologists have noticed that in some species, plants that seem to die come back two or more years after their last appearance. John Harper, the pioneering ecologist who set the stage for modern plant ecology with his writings on evolutionary approaches to studying the Plant Kingdom and his now quintessential textbook on plant population ecology, suggested that these plants seemed to defy the finality of death, and that clearly this could not be so. Rather than being resurrected from the dead, these orchids and other long-lived herbaceous plants actually live underground without sprouting for years at a time, in a state referred to as “vegetative dormancy”. By not sprouting, they also do not photosynthesize, nor do they flower and reproduce, seemingly defying the very definition of a plant.

I first encountered my first dormancy-prone species in Cypripedium parviflorum, the small yellow lady’s slipper, as someone charged in helping to manage it. This rare species is of conservation concern, as are so many other dormancy-prone species. Although these species are of conservation concern because of the destruction of their habitat due to farming and suburban expansion, conservation management plans often include little provision for active management because the ecologies of these species are not well understood. One particular problem is that the ecology of vegetative dormancy is not well understood, and so it is difficult to manage a species that undergoes it. For example, is dormancy a sign that the plant is weakening and dying? Or is it a buffer against environmental stress? Is it adaptive, or not?

JEcol-2013-0767.R3_Shefferson

Many hypotheses have been explored for why and how vegetative dormancy occurs. In our article, we present the first strong evidence that this phenomenon is actually due to the long-term cost of high growth to survival, because high growth sometimes leads to a shortage of stored energy reserves that can exacerbate mortality in harsh years. This is important, since dormancy-prone species are often rare and endangered, and an accurate understanding of their life histories is required to understand their population dynamics. Ultimately, without this understanding, we cannot develop effective management plants for them.

Our next step in this research is to see how general this pattern is – is dormancy so common for the same reason in other species, or has it evolved for a number of reasons across the Plant Kingdom? Our own suspicion is that if dormancy is always adaptive, then the reason for it is likely to change with important ecological or life history characteristics, such as lifespan, mode of reproduction, and growth form.

Richard Shefferson

Article

“Life-history costs make perfect sprouting maladaptive in two herbaceous perennials” by Shefferson, Warren II & Pulliam. The paper is currently in Early View.

Editor’s Choice 102:4

The Editor’s Choice for the next issue of Journal of Ecology is “An ideal free distribution explains the root production of plants that do not engage in a tragedy of the commons game” by McNickle and Brown. Read the below commentary on the paper written by Journal of Ecology Editor Mark Rees. Author Gordon McNickle has also provided some photos, which are at the bottom of this post. The next issue of the Journal will be online very soon.

Blissful indifference or escalation?

Imagine you’re in a dark room and there are diamonds on the floor, some areas have lots of diamonds so you search them carefully, whereas others have few and so you briefly search there. You wander around collecting the diamonds and smugly smiling to yourself, then you realise there is someone else in the room and they’re stealing “your” diamonds! What do you do? You could just do as before, ignore the presence of the other person, and providing they do the same end up with roughly ½ the diamonds or you could start searching frantically trying to increase your share. This is exactly the dilemma plants face when foraging for resources underground.

Let’s assume you start searching more quickly, so you increase your share of the diamonds. Soon your competitor realises what you’ve done and so they search more quickly themselves. At this point you’re both searching more quickly and so you both end up with ~½ the diamonds. You escalate again, now you’re running around frantically searching, your competitor responds in kind, so you’re both running around like ants under a magnifying glass on a hot summer’s day. Bang! Your competitor runs into a wall and passes out losing all their diamonds, a smug grin crosses your face again and is promptly wiped off as you too run into a wall, pass out and lose all your diamonds. So at each escalation you’re spending more energy searching and getting the same return, or ultimately no return at all. This process is called “The Tragedy of the Commons” and was proposed by Hardin as a way of explaining why common land is often overgrazed, and similarly why fisheries are often overfished.

So what do plants do when competing for soil resources? This is the question posed by McNickle and Brown (2014) in this issue’s Editor’s Choice. It turns out that distinguishing between sensibly searching so that your returns from different areas per searching effort are equal (the idea free distribution) and escalating is much more difficult than you might expect. Using a combination of mathematical modelling and experiments with carefully chosen controls, McNickle and Brown (2014) show how to distinguish between these alternatives. They then go on test their ideas experimentally finding that Brassica rapa forages according to  –  well that would be telling, you’re going to have to go read it yourself.

Mark Rees
Editor, Journal of Ecology

Dunes 101.1IMG_20120409_132606IMG_20120413_154219

How much of the world is woody?

What proportion of the species in the world are woody?

There are many ways to characterize a plant, but perhaps everyone (including the first known botanist Theophrastus of Eresus, one of Plato’s students) starts with a simple distinction between woody and herbaceous plants.

For a recent research project on the evolution of this simplest plant trait stemming from a NESCent working group, we needed an estimate of the proportion of woody species in the world. The problem seemed tractable; perhaps even something we could readily look up in Wikipedia. However, when we looked, we found nothing in everyone’s favourite internet look up site; nor did we find anything in ISI, Google Scholar, or even more broadly in Google.

This absence of information led us to ponder how, in the era of “big data”, could such a simple question remain unknown? Splitting plants into herbaceous and woody dates back to Theophrastus (in ~300 BC), but still by all appearances such a partitioning of biodiversity into different forms is a blind spot in the accumulated scientific knowledge. The diagram represents the problem we faced:

Fitzjohn et al. figure

As shown in the diagram, while we think we live in the time of “big data” with databases representing tens of thousands of species, our data are typically still a small fraction of global biodiversity. We should point out that for our NESCent project, we assembled the largest single plant trait database to date for one of the simplest possible traits–woodiness–and we still only reached values for 16% of known species (Zanne et al. 2014). GenBank which is the most successful crowd sourced open data effort in our field is only doing slightly better. The take home message then is that an understanding of global biodiversity that goes beyond simply a name is still absent.

Part of the problem is that today’s biologists, despite our access to modern gadgets, are still lagging behind Carl Linnaeus and those that continued after him. Global data require global standards, and in the Systema Naturae there was a clear filing cabinet in which to name and add newly encountered species. But for functional and genetic data we have not (until recently) had analogous filing cabinets for genes or functional traits. Thus despite our access to better tools, those interested in either functional or molecular diversity are still playing a big game of catch up.

All this is to say that there are a lot of missing data, and even if we wanted to rely upon the current data for woodiness to estimate the true values, we are faced with an additional problem that of sampling bias. The species that we do have data for are biased geographically, functionally, and phylogenetically. The temperate climates are over-sampled and economically important species are over-sampled. Oddities are often studied, while average species far from the nearest herbarium are rarely encountered by scientists or sampled for their genetic or functional traits.

These collection biases mean that it is not a simple task to estimate any summary statistics for global diversity based on the data currently at our fingertips, including addressing the question we started with–how many species in the world are woody. Based on the challenges we faced in both data discovery and sampling biases, the light finally dawned as to why the question wasn’t already known—the question’s apparent simplicity was in fact misleading. As everyone learns in introductory biology sampling bias is a serious problem.

All is not lost, however: we can once again turn to Linneaus’ filing cabinet to provide us with a way forward. What we found when searching in his cabinets was that most genera are either all woody or all herbaceous–only a few have a mix of herbs and woody plants. Families are less bimodal but many still are solely composed of one sort of plant or the other. This property of genera and families turns out to be quite a powerful observation, and with a new method we were able leverage this property to work our way toward what turned out to be a robust estimate of the percentage of species in the world are woody. Our estimate is between 45 and 48% (FitzJohn et al. 2014).

Now that we have an answer to our initial question, many other questions can follow suit. For instance, we can use similar approaches to ask the following, as long as taxonomic membership conveys something about a species’ likely function. What proportion of plants are pollinated by animals? What proportion of mammals are herbivores? What percentage of insects fly? While these seem like basic, Wikipedia style questions, their answers are currently unknown to both science and google searches. These basic questions about the world will provide fundamental insight into how global functional diversity is partitioned across space and time. Furthermore they are a first step towards understanding both macro-ecological and macro-evolutionary patterns–to understand the evolution of woody and herbaceous lifeforms in relation to climate (Zanne et al. 2014) on a global scale, we need to know some distribution of these traits across the tree of life.

These global questions about functional diversity are simple, but we are only now assembling the tools that let us answer them.

Will Cornwell & Rich Fitzjohn

References

FitzJohn, R. G. et al. (2014) How much of the world is woody? Journal of Ecology. doi:10.1111/1365-2745.12260

Smith, S. A., Beaulieu, J. M., Stamatakis, A., & Donoghue, M. J. (2011) Understanding angiosperm diversification using small and large phylogenetic trees. American Journal of Botany doi:10.3732/ajb.1000481

Zanne, A. E., Tank, D. C., Cornwell, W. K., Eastman, J. M., Smith, S. A., FitzJohn, R. G., … & Beaulieu, J. M. (2014) Three keys to the radiation of angiosperms into freezing environments. Nature doi:10.1038/nature12872

Editor’s Choice 102:3

We anticipate that issue 102:3 will be online this week. Consider it an Easter treat without the calories!

The Editor’s Choice paper from this issue is Restoration of a megaherbivore: landscape-level impacts of white rhinoceros in Kruger National Park, South Africa” by Cromsigt & te Beest.

The Swedish University of Agricultural Sciences published a press release on this paper earlier this year.

Editor’s Choice 102:3

Large-bodied herbivores – megaherbivores – have been lost from many ecosystems worldwide.  A growing appreciation of the ecological roles that they play has led to reintroductions of megaherbivores into some ecosystems, for example of muskox and wisent into a “Pleistocene Park” in Siberia, or even calls for surrogates to be introduced into others, such as elephants as replacements for long-extinct marsupial megaherbivores in northern Australia.

So far there is little evidence to show what the consequences for ecosystems could be that result from “rewilding” through the reintroduction of megaherbivores.  A new study by Cromsigt and te Beest provides insights into their effects.  In Kruger National Park, South Africa, white rhinoceroses were hunted to extinction in 1896.  They were reintroduced to the Park between 1961 and 1972, most of them to the south-western corner of the Park, and much of the Park remains unoccupied by white rhinoceroses.  Thus there are zones in the Park with either no rhinos, sparse rhino populations, and comparatively dense rhino populations.  Cromsigt and te Beest studied the impacts of the rhinos on the savanna grasslands of the Park.  They capitalised upon the “natural” experiment that the reintroductions presented, focussing on zones with sparse and dense rhino populations.

Photo credit: Jan Graf

Photo credit: Jan Graf

Rhinos aren’t the only megaherbivores present in Kruger National Park: there are also African elephants and hippopotami (the latter don’t venture far from rivers).  There are also a large range of other grazers, including buffalo, wildebeest, zebras and various antelopes.  Yet the effects of the rhinos could be clearly distinguished.  Where their numbers were greatest, short grasses were more prevalent and there were many more distinct grazing lawns that are maintained by the rhinos.  These effects were consistent across more fertile soils derived from basalts and less fertile soils derived from granite.

Cromsigt and te Beest conclude that the rhinos are important drivers of grassland heterogeneity in these savannas.  An intriguing possibility supported by observational data in this study is that this could also be driven, at least on the infertile granitic soils, by an interaction between rhinos and termites.  Grazing lawns on these soils were usually close to termite mounds, which the authors think may be linked to locally enhanced nutrient availability.  This begs further study about whether there may be positive feedbacks between termites, rhinos, and the distinct plant communities that develop in the grazing lawns.

Time for such studies however may be running out.  Cromsigt and te Beest note that poaching pressure on white rhinos, should it continue at current rates, would result in a second extinction of these animals in Kruger National Park within 20 years, and would end of this “rewilding” experiment.  It is a grim prospect that the opportunities presented to determine the ecosystem effects of a rhino population, reintroduced barely thirty years ago, could instead, in future years, give way to a chance to document trophic downgrading after these megaherbivores have gone.

Peter Bellingham
Associate Editor, Journal of Ecology