If things had turned out differently in past millennia, modern-day animal lovers wouldn't have to fly to Kenya to go on safari. North America was once overrun with tourism-worthy animals: Aside from the iconic woolly mammoth, there were saber-toothed cats, giant sloths, and short-faced bears more than twice as massive as a grizzly. We're still not sure what happened to them, but a new study in Nature attempts to untangle the whodunnit.
Since dozens of these "megafauna" species disappeared from the Americas, Eurasia and Australia just as humans were arriving, it's tempting to blame ourselves. The human love of the mixed grill, after all, runs deep.
But the mass extinction, beginning around 50,000 years ago, coincided with another key event: the end of the last ice age and shift to a warmer climate. So controversy over what killed off the ancient megafauna has persisted.
To tackle the large-scale, globe-spanning question, a large and globe-spanning team of researchers decided to take it species by species. Even though the animals went extinct around the same time, they might have been individually done in by different factors. The researchers looked at ancient animal remains and human remains from around the world, as well as DNA samples from the megafauna. The genetic material told them about each species' diversity over time (species with more genetic diversity are better able to adapt to changing environments), and the overlap of human and animal remains showed when and where we coexisted.
Woolly rhinoceros: Not our fault.
The study focused on just six animals. All of them were herbivores living in North America or Eurasia, and some of them have living members today but inhabit a greatly reduced range.
The woolly rhinoceros, pictured above, used to live in Eurasia but is now extinct. The researchers found that the woolly rhino's population size was actually increasing well after the species came in contact with humans, and there's no evidence that we commonly preyed on (or even came in contact with) the rhino. This would seem to vindicate us--it was probably the warming climate, not humans, that wiped out the woolly rhinoceros.
Wild horse: Our fault.
The wild horse or tarpan, Equus ferus, is also extinct today (and not to be confused with wild populations of domestic horses). The species maintained a large Eurasian population well into the warming period, suggesting that climate change wasn't what ultimately killed it. The overlap between wild horse and human populations, as well as the abundance of wild horse remains at human archeological sites, hints that we may have hunted the species to death.
Woolly mammoth: ?
As for the poor mammoth, the data are disappointingly unclear. Our ranges overlapped in both Eurasia and North America, and ancient North Americans are known to have hunted the mammoth. But the mammoth's population in Eurasia, like the woolly rhino's, was still increasing after it came in contact with humans, and its range may have begun to shrink as the weather warmed. It could have been either culprit that ultimately killed the mammoth, or a fatal combination of human hunting and climate change together.
That fatal combination is what makes this sort of research--the cold cases of paleontology, if you will--urgent today. We're again experiencing warming, though it's happening much, much faster than in the age of the mammoths. Simultaneously, we're pushing species out of their habitats or poaching them into extinction. The authors of the new study didn't find any one feature, such as a genetic signature or a distinct pattern of distribution, that predicted which animals lived and which died. That means we're no closer to guessing which of today's species will survive climate change and human involvement--like the reindeer, which lived through the extinction of its fellow megafauna and thrives today--and which will go the way of the mammoth.
Images: PLoS/Mauricio Anton
Lorenzen, E., Nogués-Bravo, D., Orlando, L., Weinstock, J., Binladen, J., Marske, K., Ugan, A., Borregaard, M., Gilbert, M., Nielsen, R., Ho, S., Goebel, T., Graf, K., Byers, D., Stenderup, J., Rasmussen, M., Campos, P., Leonard, J., Koepfli, K., Froese, D., Zazula, G., Stafford, T., Aaris-Sørensen, K., Batra, P., Haywood, A., Singarayer, J., Valdes, P., Boeskorov, G., Burns, J., Davydov, S., Haile, J., Jenkins, D., Kosintsev, P., Kuznetsova, T., Lai, X., Martin, L., McDonald, H., Mol, D., Meldgaard, M., Munch, K., Stephan, E., Sablin, M., Sommer, R., Sipko, T., Scott, E., Suchard, M., Tikhonov, A., Willerslev, R., Wayne, R., Cooper, A., Hofreiter, M., Sher, A., Shapiro, B., Rahbek, C., & Willerslev, E. (2011). Species-specific responses of Late Quaternary megafauna to climate and humans Nature DOI: ... Read more »
Lorenzen, E., Nogués-Bravo, D., Orlando, L., Weinstock, J., Binladen, J., Marske, K., Ugan, A., Borregaard, M., Gilbert, M., Nielsen, R.... (2011) Species-specific responses of Late Quaternary megafauna to climate and humans. Nature. DOI: 10.1038/nature10574
Animal behaviours can sometimes jump out at you by their similarity to the kinds of things humans do. Most recently, I came across this video of golden orb-web spiders. Dominating the picture is a large speckled black and white female, confidently waiting for her next unsuspecting meal to arrive. What might not be so obvious is the weedy orange male, running scurrilously on her back. Not exactly a very human-like behaviour, I hear you say. Well, I answer back, you don’t know what he’s doing there.... Read more »
Shichang Zhang, Matjaž Kuntner, & Daiqin Li. (2011) Mate binding: male adaptation to sexual conflict in the golden orb-web spider (Nephilidae: Nephila pilipes). Animal Behaviour. info:/doi:10.1016/j.anbehav.2011.09.010
Lurking the background of many previous articles here at Per Square Mile is a recently formulated framework that describes everything from the heart rate of a mouse to the aorta size in a blue whale. It’s called the metabolic theory. Metabolic theory’s origins span two states and six decades. Max Kleiber originally formulated the basic [...]... Read more »
Enquist, B., Brown, J., & West, G. (1998) Allometric scaling of plant energetics and population density. Nature, 395(6698), 163-165. DOI: 10.1038/25977
Less than 3% of mammals are thought to be socially monogamous. However, with the advent of molecular techniques for establishing paternity, some presumably “monogamous” mammals may exhibit relatively high levels of extra pair paternity (EPP), or “cheating.”
Arctic fox (Vulpes lagopus, Figure 1) are a case in point. The arctic fox forage alone, but the social group usually consists of a breeding pair and their young (and occasionally a non-breeding female). Until just a few years ago Arctic foxes were considered strictly monogamous. ... It is still not clear how common EPPs are in Arctic fox populations.
...Paternal care (care provided by the father) may help females raise successful litters in harsh Arctic environments. Scientists predict that paternal care may be critical to pup survival when food abundance is low, or when the distribution of food is very patchy. When food is abundant in one area, the density of breeding fox pairs will also be high in that area, leading to increased probability of females seeking extrapair copulations.
Three Canadian scientists (Cameron et al., 2011) recently tested these predictions on Bylot Island in the Arctic (Figure 2). On this island, the presence of a goose colony provided a localized, high-density food source (spatial variation) and cyclic eruptions of lemming populations provided a temporally variable food resource.
...Arctic fox study area (gray polygon) and goose colony (dark polygon) on Bylot Island, Nunavut, Canada. Active fox dens are indicated with open triangles and inactive dens by black triangles. Dens are identified by a three digit code followed by the last two digits of the year and an E if EPPs were detected or I if only intrapair paternity was detected.
...The mating systems of Arctic foxes on Bylot Island were monitored over five years using a combination of behavioral observation of family groups and molecular analyses. The results indicate that social monogamy is the rule, but extrapair paternity is relatively common. At least 31% of pups were fathered by a male who was not part of the “family group.” Furthermore, the probability of EPP was correlated with food availability. Incidences of EPP was greatest with in the goose colony (86%) and declined steeply with increasing distance from the goose colony (Figure 3).
...Mating system of female arctic foxes as a function of the distance between their den(s) and the center of the goose colony on Bylot Island, Canada. Litters (open circles) were the result of either intrapair (0.0) or extrapair copulations (1.0).
...The researchers conclude that, “In arctic foxes, behavioral strategies, such as extraterritorial movements and EPP, that increase gene flow are probably important for the genetic structure of populations.”
...Cameron, C., Berteaux, D., & Dufresne, F. ... Spatial variation in food availability predicts extrapair paternity in the arctic fox Behavioral Ecology, 22 (6), 1364-1373 DOI: 10.1093/beheco/arr158
... Read more »
Cameron, C., Berteaux, D., & Dufresne, F. (2011) Spatial variation in food availability predicts extrapair paternity in the arctic fox. Behavioral Ecology, 22(6), 1364-1373. DOI: 10.1093/beheco/arr158
Understanding the extent to which pre-Columbian peoples altered and deforested the Amazon basin is key in order to assess i) the impact that pre-Columbians had on global climate during the Holocene [Dull et al., 2010] and ii) the resilience of the Amazon rainforest to human disturbance [Bush and Silman, 2007]. The first point is essential to our understanding of the major drivers behind climate fluctuations during the Holocene, and hence to help predict future fluctuations. The second point is important to inform conservation and development policies in Amazonia. Unfortunately, the scarcity of archaeological and paleoecological data from the Amazon Basin has favoured the proliferation of “reconstructions of the past” that are hard to test. Some of these theories have reached broad audiences thanks to the echo provided by popular media and books [Mann, 2005]. New archaeological findings that suggest the existence of complex societies in pre-Columbian Amazonia have led some researchers to define the Amazon Basin as a “manufactured landscape” or an “anthropogenic cornucopia” [Balée and Erickson, 2006; Erickson, 2008]. There are 3 different lines of research that can help assess whether or not these reconstructions are accurate. One is to focus on those regions that host important archaeological remains and study the evidence of complex societies. This work is already being carried out by some archaeologists such as Heiko Prümers. The second area of research is to examine if and how the development of complex societies in the region were influenced by local environmental constraints and opportunities. This is the kind of work that I am carrying out in the Llanos de Moxos and hope to discuss in another post quite soon J (briefly introducedhere…). Another area of research that can help us understand the Amazon’s past is to test if the level of human disturbance associated with the sites where evidence of complex societies has been discovered can be extrapolated to the rest of the Amazon basin. A milestone paper that looks at the latter, and that has been often cited in this blog, is Bush and Silman (2007).A few weeks ago, The Holocene published on-line a new paper that delves deep into this question, providing interesting new data [McMichael et al., 2011]. McMichael et al. test the hypothesis that human disturbance was widespread in the Amazon Basin during pre-Columbian times (as some authors have suggested). If this hypothesis is true and the disturbance was widespread then, the authors argue, the sites where permanent settlements were likely to have established should show sedimentary evidence of that disturbance. Hence, they cored lakes ( considered by the authors as preferred settlement sites) and sampled soils in the vicinity of the lakes and looked at charcoal and phytoliths. They found that charcoal record was discontinuous and localized. They then concluded, based on the sedimentary evidence: “Our data suggest that while all of the settings examined were occupied or used, the halo of influence around each was limited. It should not be assumed that intensive landscape transformations by prehistoric human populations occurred throughout Amazonia or that Amazonian forests were resilient in the face of heavy historical disturbance”. The paper suggests that pre-Columbians developed into complex societies and substantially altered their environment in those areas where environmental conditions were favourable. They predict that these sites can be found along the main rivers and in those parts of the Amazon Basin that are characterized by a strong seasonality (like the Llanos de Moxos).In my opinion this paper is a beautiful piece of Science and I invite you to read it!C. H. McMichael, M. B. Bush, D. R. Piperno, M. R. Silman, A. R. Zimmerman, & C. Anderson (2011). Spatial and temporal scales of pre-Columbian disturbance associated with western Amazonian lakes The Holocene : 10.1177/0959683611414932... Read more »
C. H. McMichael, M. B. Bush, D. R. Piperno, M. R. Silman, A. R. Zimmerman, & C. Anderson. (2011) Spatial and temporal scales of pre-Columbian disturbance associated with western Amazonian lakes. The Holocene. info:/10.1177/0959683611414932
By Matt Wood
Sometimes scientific discoveries happen by accident. Henri Becquerel discovered radioactivity when a uranium rock he left wrapped up in a drawer with some X-ray equipment imprinted itself on a photographic plate. Alexander Fleming discovered penicillin when he noticed that mold growing in a staphylococcus culture was killing all the bacteria around it. In [...]... Read more »
Pfister, C., McCoy, S., Wootton, J., Martin, P., Colman, A., & Archer, D. (2011) Rapid Environmental Change over the Past Decade Revealed by Isotopic Analysis of the California Mussel in the Northeast Pacific. PLoS ONE, 6(10). DOI: 10.1371/journal.pone.0025766
Orchids have some of the most remarkable pollination relationships of all the flowering plants. Their flowers are adapted into wild shapes for placing packets of pollen on precisely the right part of a pollinator’s body, and many species attract pollinators with lures that are somewhat kinkier than simply offering nectar—such as mimicking a female pollinator’s [...]... Read more »
Gaskett, A. (2011) Orchid pollination by sexual deception: pollinator perspectives. Biological Reviews, 86(1), 33-75. DOI: 10.1111/j.1469-185X.2010.00134.x
Ramirez, S., Eltz, T., Fujiwara, M., Gerlach, G., Goldman-Huertas, B., Tsutsui, N., & Pierce, N. (2011) Asynchronous diversification in a specialized plant-pollinator mutualism. Science, 333(6050), 1742-6. DOI: 10.1126/science.1209175
By Bendert Katier Monday October 31, 2011
This month’s magazine is themed Apocalypse Now. Or, what seems to be more appropriate, Apocalypse Not. Because although Judgement Day has been predicted many, many times, it is still not upon us. Wonder if, when, and how it will happen? Check out this issue.... Read more »
Bartlett, A. (1994) Reflections on sustainability, population growth, and the environment. Population and Environment, 16(1), 5-35. DOI: 10.1007/BF02208001
I highlighted this paper a few days ago as looking interesting, but after reading it, I felt like expanding a bit. The paper is by Rubbo et al (2011, Aquatic Sciences) and is entitled "Species loss in the brown world: are heterotrophic systems inherently stable?"
Before I get into this paper, I think it is probably worthwhile to put this in some sort of perspective. There are a few ... Read more »
Michael J. Rubbo, Lisa K. Belden, Sara I. Storrs-Mendez, Jonathan J. Cole, & Joseph M. Kiesecker. (2011) Species loss in the brown world: are heterotrophic systems inherently stable?. Aquatic Sciences. info:/
Finding enough food to sustain the energy costs of foraging is a problem faced by all mammals. However, it is made more difficult for mammals that feed on unpredictable and limited prey. ... Molossus molossus (Figure 1), for example, is an aerial insectivore that forages in groups over large areas. Not only must they expend large amounts of energy to fuel these foraging flights, but they only forage for approximately one hour each night. How can they maintain a positive energy balance with such high energetic costs and apparently low energy gains?
...Previous research shows that flying bats expend roughly 15 times the energy they do at rest. Furthermore, small bats have higher resting metabolic rates and lose more heat because of their relatively high surface area to volume ratio. Thus, small aerial feeding bats in temperate zones often enter torpor each day as a way to conserve precious energy.
...German researchers (Dechmann et al. 2011) may have found the answer. They attached tiny transmitters to molossid bats that were designed to measure heart rates. These transmitters sent back data for 48 hours before falling off the bats. The data was used to estimate energy budgets over a two-day period. The researchers hypothesized that the daily energy expenditure (DEE) would be high in these neotropical bats because they have very brief foraging periods and do not undergo daily torpor.
The researchers were surprised to find that these bats exhibited low mean heart rates. This corresponded to a DEE of only half what a similarly sized bat would experience. In addition, field metabolic rates (FMRs), predicted from doubly labeled water were 10 times higher than the DEE predicted from heart rate telemetry for a 10g bat. How were the molossid bats in this study able to conserve so much energy?
One possibility is that molossid bats lower their energy consumption during roosting in a manner similar to daily torpor (Figure 2). The heart rate data reveal that molossid bats do reduce their heart rates while roosting, but not so much that it would be called “torpor.” The authors suggest that “lowered metabolism” in tropical bats may be much more common that previously believed.
...Heart rate measurements from seven bats tracked for 48 hours. The two days were averaged and plotted over a 24 hour period.
...Dechmann, D., Ehret, S., Gaub, A., Kranstauber, B., & Wikelski, M. ... Low metabolism in a tropical bat from lowland Panama measured using heart rate telemetry: an unexpected life in the slow lane Journal of Experimental Biology, 214 (21), 3605-3612 DOI: 10.1242/jeb.056010
... Read more »
Dechmann, D., Ehret, S., Gaub, A., Kranstauber, B., & Wikelski, M. (2011) Low metabolism in a tropical bat from lowland Panama measured using heart rate telemetry: an unexpected life in the slow lane. Journal of Experimental Biology, 214(21), 3605-3612. DOI: 10.1242/jeb.056010
Yesterday, an article caught my attention because the subject was a mysterious creature that is rarely seen or photographed. The Rainbow Snake, Farancia erytrogramma, is a large species highly-associated with wetlands. It is one of the most visually-striking species of wildlife that can be found in the southeastern United States. Covered by dark and glossy scales, bright red lines run... Read more »
Neill, W. (1964) Taxonomy, Natural History, and Zoogeography of the Rainbow Snake, Farancia erytrogramma (Palisot de Beauvois). American Midland Naturalist, 71(2), 257. DOI: 10.2307/2423288
Durso, A.M., J.D. Willson, & C.T. Winne. (2011) Needles in haystacks: estimating detection probability and occupancy of rare and cryptic snakes. Biological Conservation, 1508-1515. info:/
Broomcorn millet is a bit of a puzzle. You start to get archaeobotanical evidence for cultivated Panicum miliaceum in both China and Europe at about the same time before 7000 BP. Independent domestication or movement along the fabled Silk Road (like wheat)? And if the latter, in which direction? You can hear the conundrum set [...]... Read more »
HUNT, H., CAMPANA, M., LAWES, M., PARK, Y., BOWER, M., HOWE, C., & JONES, M. (2011) Genetic diversity and phylogeography of broomcorn millet (Panicum miliaceum L.) across Eurasia. Molecular Ecology. DOI: 10.1111/j.1365-294X.2011.05318.x
It’s no surprise that Homo sapiens dominates the Earth. After all, we’re resourceful, social, and smart. No, the surprise is how we did so in just 50,000 years. Such a pace is unprecedented, especially for a long living, slow reproducing species such as ours. Intelligence and opposable thumbs certainly helped, but we aren’t the only ones who [...]... Read more »
Hamilton, M., Burger, O., DeLong, J., Walker, R., Moses, M., & Brown, J. (2009) Population stability, cooperation, and the invasibility of the human species. Proceedings of the National Academy of Sciences, 106(30), 12255-12260. DOI: 10.1073/pnas.0905708106
A new paper from Dickau et al., recently published on-line bythe Journal of Archaeological Sciences, brings us back to one of the favouritethemes of this blog: pre-Columbian agriculture in the Amazon Basin. The work ofDickau et al. confirms the findings of Bruno (2010), also a co-author in Dickauet al., and provides more data from new sites. They have analysed botanicalremains from 2 pre-Columbian monumental mounds east of Trinidad (LomaSalvatierra and Loma Mendoza) and from another site, a ring ditched villagecalled “Granja del padre”, about 200 Km far from the mounds, close to BellaVista(see location in Fig 1 and photo of the ring village in Fig 1a). Analysisof macro and micro botanical remains from Loma Salvatierra and Mendoza and fromGranja del padre shows that the most common cultivated species was maize (Zea mais L.). It was present in almostall samples and fairly abundant. The second most common cultivated speciesseems to have been manioc (Manihot esculenta Crantz).Interestingly, maize was also more frequently encountered on ceramic graters,which were thought to be processing tools for grating manioc . They recoveredstarch grains from artefacts and clearly identified 5 grain of yucca vs. 115 ofmaize. This is really surprising becausemanioc is a good source of energy and far easier to cultivate than maize. Ceramicgraters can be found all over the Llanos.It can be easily assumed that yucca was cultivated all over the Llanos de Moxosbecause, provided good drainage, yucca can grow even on very bad, acid,aluminium rich soils. I was actually persuaded that raised fields, elevatedearth platforms that were user as agricultural surface, were built to providedrained land for manioc. But now, it seems that maize, and not manioc, was themost important crop in the Llanos de Moxos.Figure 1. The Llanos de Moxos. Red triangles are the Salvatierra and Mendoza mounds.a) Google Earth photo of the Granja del padre with the approximate locations ofthe archaeological excavations in yellow.If this data is confirmed by other researches, we could start consideringceramic graters (Fig 2) as a proxy for maize consumption. As ceramic gratersare found everywhere in the Llanos de Moxos, a direct link between ceramicgrates and maize would indicate that maize was used all over the region.Figure 2. Fragment of a ceramic grater from the Llanos deMoxosThis opens up a very interesting topic for future research:was maize cultivated in all the sites where it was consumed? This is not atrivial question because maize is a very demanding crop: it needs manynutrients and a lot of water, but rots if the soil is waterlogged. In theLlanos de Moxos soils and hydrology change a lot from one place to another. Forexample, while soils in the region of the Salvatierra and Mendoza mounds formover fertile mid-Holocene fluvial sediments (Lombardo et al. coming soon, Ihope J ),la Granja del padre is found on saprolites (rotten granite rocks), very acidand poor in nutrients. Moreover, in the region of Bella Vista, no raised fieldsor Amazonian Dark Earths have been reported. So, did they grow maize usingslash and burn agriculture? If so, this would have greatly limited potentialpopulation density in the area, as slash and burn agriculture is considerably extensive.Each family needs at least 30-40 hectares of forest for cultivation and farmore as a reservoir for hunting and medicinal plants. Or was maize “imported” fromother regions? Exchanged for other goods? The estimation of pre-Columbian populationdensity, and the extent of pre-Columbian de-forestation, is a controversialissues among ecologists, geographers and archaeologists working in Amazonia. Morestudies like that of Dickau et al. are needed in order to shed some light on thepast of Amazonia during the late Holocene. Their work adds important new datato the discussion, although we are still far from fully understanding what wasgoing on in the Bolivian lowlands between 2000 and 500 BP.Ruth Dickau, Maria C. Bruno, José Iriarte, Heiko Prümers, Carla Jaimes Betancourt Irene Holst, & Francis E. Mayle (2011). Diversity of cultivars and other plant resources used at habitation sites in the Llanos de Mojos, Beni, Bolivia: Evidence from macrobotanical remains, starch grains, and phytoliths Journal of Archaeological Science : 10.1016/j.jas.2011.09.021... Read more »
Ruth Dickau, Maria C. Bruno, José Iriarte, Heiko Prümers, Carla Jaimes Betancourt Irene Holst, & Francis E. Mayle. (2011) Diversity of cultivars and other plant resources used at habitation sites in the Llanos de Mojos, Beni, Bolivia: Evidence from macrobotanical remains, starch grains, and phytoliths. Journal of Archaeological Science. info:/10.1016/j.jas.2011.09.021
Species of the near future, like a new sweater you accidentally put through a tumble-dry cycle, may be smaller and less useful than you remember them. Organisms from polar bears to plants to farmed fish are already losing stature. As the world gets hotter and rainfall gets more sporadic, countless other species are expected to shrink, too--provided they don't disappear altogether.
The authors of a new paper in Nature Climate Change compiled data from dozens of studies on species size and climate change. They had reason to expect that many species would be shrinking in response to global warming. Animals and plants have already been observed breeding earlier, flowering sooner, and gradually shifting their ranges toward the poles (and cooler temperatures). Additionally, the fossil record tells us that invertebrates and small mammals shrank during ancient periods of warming. On those occasions, though, the thermostat was turned up gradually--nothing like today.
The review found that 38 species of animals and plants have recently shrunk. The shrinkage wasn't universal, though; an equal number of species have been observed not shrinking in recent years, or provided equivocal results. And a handful of species have actually increased in size (more on them in a moment).
The species seen shrinking include representatives from the mammals, birds, reptiles, amphibians, fish, and trees. There's reason to believe that these species are trendsetters, not outliers, and that more of the so-far unchanging species will soon follow in their footsteps (or hoofsteps or wakes). If climate change is to blame for miniaturizing animals and plants, then this effect should become more obvious as the earth gets warmer.
And according to experimental evidence--not just the circumstantial evidence of species happening to shrink during the past few decades--climate change is to blame. Controlled experiments have shown that increased temperatures cause plants, fish, marine invertebrates, beetles and salamanders to grow smaller. Other studies have found that reduced precipitation produces smaller mammals, frogs and toads, and tropical trees. In the ocean, acidification caused by increased carbon dioxide in the water is known to impede the growth of corals, scallops, and other animals that build calcified bodies for themselves. Acidification also slows the growth of phytoplankton, the microscopic plants that hold up the whole ocean ecosystem. (And, don't forget, ocean acidification creates ambidextrous fish.)
There are a few ways that warmer temperatures could shrink species. In "cold-blooded" or ectothermic animals, including fish, reptiles and amphibians, a higher temperature speeds up the metabolism. Unless animals can readily find more calories to consume, this means they'll burn through their fuel faster and have fewer resources left over for growing their bodies.
For animals that maintain their metabolic rate on their own, namely birds and mammals, shrinkage might have more to do with a lack of resources. If heat or drought kill (or shrink) the species that animals feed on, they'll have to compete more to stay alive. Undernourished animals, including humans, don't grow as big as well-nourished ones.
Some regions, rather than experiencing drought, are expected to become wetter with climate change. But even these areas will have more variation in rainfall than they're accustomed to--that is, there could be periods of drought in between the rainy periods. Less consistent rain will cause plants to shrink or die. Even though increased carbon in the atmosphere might be expected to give a boost to plant life (it's called the greenhouse effect, after all), plants can't take advantage of that extra carbon without sufficient water and nutrients and a comfortable temperature. The few plant species studied so far have shriveled, not grown, in response to climate change.
Over successive generations, evolution might favor smaller individuals within species: Those that need fewer resources might be more likely to survive. The survivors, then, would pass their small-bodied genes to their offspring, and the effects of climate change would be written into animals' genomes for good.
As for those few species that are growing instead of shrinking? They're mostly at high latitudes, where a slight increase in temperature is a welcome relief from the cold. As temperatures rise even more, those species might not be so happy with the change. The species that are most likely to benefit from increased temperatures, or at least not to be too bothered, are predators that can adjust their diet to a wide range of prey. Certain invasive species, which have already demonstrated their handiness at eating anything available to them and adapting rapidly to changing conditions, might also be unscathed.
The authors point out that if every species on the planet shrank at the same rate, we'd all be fine: Within each Polly-Pocket ecosystem, everything would stay in balance. But since species are responding differently to climate change, with some already shrinking and others not, we can expect to see food chains getting bunched up or broken. As those lower on the food chain grow smaller (or, failing to adapt, go extinct altogether), species that eat them will find less food in their meals than they're used to.
This applies to humans, too. Both farmed and wild fish have already been observed shrinking, and heat and drought threaten our crops. Meanwhile, of course, the human population is growing. As climate change leads to food shortages for various groups of people, and undernourished children fail to grow as large as their parents, then even the human species might start shrinking.
Sheridan, J., & Bickford, D. (2011). Shrinking body size as an ecological response to climate change Nature Climate Change DOI: 10.1038/nclimate1259
... Read more »
Sheridan, J., & Bickford, D. (2011) Shrinking body size as an ecological response to climate change. Nature Climate Change. DOI: 10.1038/nclimate1259
In a much anticipated study published this month in Nature, Jonathan Foley and colleagues describe the environmental and human impacts of today's agricultural systems, and they identify four big ideas for solving these problems on a global scale.
1. Freeze the land footprint of agriculture:
"The food production benefits of tropical deforestation are often limited, especially compared to the environmental damages accrued... Agricultural production potential that is 'lost' by halting deforestation could be offset by reducing losses of productive farmland and improving yields on existing croplands."
2. Improve yields:
"The best places to improve crop yields may be on underperforming landscapes, where yields are currently below average... There are significant opportunities to increase yields across many parts of Africa, Latin America and Eastern Europe, where nutrient and water limitations seem to be strongest. Better deployment of existing crop varieties with improved management should be able to close many yield gaps, while continued improvements in crop genetics will probably increase potential yields into the future... If yields for these 16 [food and feed] crops were brough up to only 75% of their potential, global production would increase by 1.1. billion tonnes, a 28% increase... Closing yield gaps without environmental degradation will require new approaches, including reforming conventional agriculture and adopting lessons from organic systems and precision agriculture."
3. Increase the efficiency of agricultural inputs:
"Our analysis reveals 'hotspots' of low nutrient use efficiency and large volumes of excess nutrients... We also find that only 10% of the world's croplands account for 32% of the global nitrogen surplus and 40% of the phosphorus surplus. Targeted policy and management in these regions could improve the balance between yields and the environment. Such actions include reducing excessive fertilizer use, improving manure management, and capturing excess nutrients through recycling, wetland restoration and other practices."
4. Shift diets and reduce waste:
"We estimate the potential to increase food supplies by closing the 'diet gap': shifting 16 major crops to 100% human food could add over a billion tonnes to global food production (a 28% increase)... Of course, the current allocation of crops has many economic and social benefits, and this mixed use is not likely to change completely. But even small changes in diet (for example, shifting grain-fed beef consumption to poultry, pork or pasture-fed beef) and bioenergy policy (for example, not using food crops as biofuel feedstocks) could enhance food availability and reduce the environmental impacts of agriculture."
And in summary:
"Our analysis demonstrates that four core strategies can - in principle - meet future food production needs and environmental challenges if deployed simultaneously. Adding them together, they increase global food availability by 100-180%, meeting projected demands while lowering greenhouse gas emissions, biodiversity losses, water use and water pollution."
Foley, J., Ramankutty, N., Brauman, K., Cassidy, E., Gerber, J., Johnston, M., Mueller, N., O’Connell, C., Ray, D., West, P., Balzer, C., Bennett, E., Carpenter, S., Hill, J., Monfreda, C., Polasky, S., Rockström, J., Sheehan, J., Siebert, S., Tilman, D., & Zaks, D. (2011). Solutions for a cultivated planet Nature DOI: 10.1038/nature10452... Read more »
by cej9f in Nothing in Biology Makes Sense!
I’ll admit it. Coevolution turns me on. It gets me up in the morning, is usually the last thing I think about before passing out at night and I’ve made more of a commitment to coevolution than any man I’ve ever been with. I’ve been an evolutionary biologist for the majority of my adult life, [...]... Read more »
Antolin, M. (2009) Evolutionary biology of disease and Darwinian medicine. Evolution: the First Four Billion Years, 281-98. info:/
I recently had a paper from a co-worker (Jason Veldboom) come across my semi-ridiculous RSS feed. This paper does something a little bit different than any other publication I've seen: Follow the elemental composition of a population and its (presumably) primary food resource through time.
The study is straight-forward, in that the authors simply sampled a filter feeding caddisfly larvae ... Read more »
Veldboom, J.A., & Haro, R.J. (2011) Stoichiometric relationship between suspension-feeding caddisfly (Trichoptera: Brachycentridae) and seston. Hydrobiologia. info:/
Today is World Food Day, as designated by the United Nations on the anniversary of the founding of the Food and Agriculture Organization in 1945, and as such is this year's Blog Action Day on the topic of food...... Read more »
Ozdogan, M. (2011) Exploring the potential contribution of irrigation to global agricultural primary productivity. Global Biogeochemical Cycles, 25(3). DOI: 10.1029/2009GB003720
Mammals are characterized by diphyodonty, only two generations of teeth, among other traits. However, a few mammals have evolved a form of continuous tooth replacement. For example, Manatees (Trichechus) add extra teeth at the back of the jaw as teeth near the front are worn away or lost. Such a conveyor-belt type of tooth replacement is exceedingly rare in mammals. The only other mammal know to exhibit continuous tooth replacement of this type is a metatherian, the pygmy-rock wallaby (Petrogale concinna). Elephants have a superficially similar type of tooth replacement, but they replace their teeth sequentially and do not form any extra teeth in the process.
As a new report in the Proceedings of the National Academy of Sciences, researchers have now added the silvery mole-rat (Heliophobius argenteocinereus, Figure 1) to the short list of mammals with continuous tooth replacement (Gomes Rodrigues et al. ... These chisel tooth rodents not only possess a conveyor-like tooth replacement, but they are also hypsodont; have high crowned teeth (Figure 2).
...A silvery mole-rat (Heliophobius argenteocinereus).
...Photos (A-C) and drawings of the teeth in Heliophoius argenteocinereus. (A-C) A lateral view of the upper and lower tooth rows with the mandible removed. (D) The pattern of dental replacement in the silvery mole-rat with the arrow indicating the direction of the movement of teeth. (From Gomes Rodrigues et al.
...The researchers propose that the conveyor-like tooth replacement evolved in the silvery mole-rat because of their “hyper-chisel tooth digging behavior; they dig tunnels with their procumbent incisors thereby exposing their cheek teeth to extremely abrasive dirt, which causes their hypsodont cheek teeth to wear rapidly.
Manatees, the pygmy-rock wallaby, and silvery mole-rats undoubtedly evolved continuous tooth replacement convergently; they have different habitats, diets, and are distantly related phylogenetically. Nevertheless, all three groups share three dental traits: extra teeth (supernumerary teeth), delayed eruption, and dental mesial drift (Figure 3). The later character occurs when cheek teeth drift forward as a result of pressure from teeth erupting at the back of the toothrow.
...Phylogenetic tree of dental characteristics related to continuous tooth replacement in several mammals. Column one is the jugal dental formula. The remaining columns represent presence mesial drift (MD), supernumerary teeth (ST), delayed dental eruption (DE), hypsodonty (H), and in column six, replacement of a premolar (P), molar (M), or continuous dental replacement (CDR). (From Gomes Rodrigues et al.
...The authors suggest that epithelial tissues involved in tooth formation may persist as a permanent dental lamina, thereby permitting continual replacement of teeth in Heliophobius.
...Gomes Rodrigues, H., Marangoni, P., Sumbera, R., Tafforeau, P., Wendelen, W., & Viriot, L. ... Continuous dental replacement in a hyper-chisel tooth digging rodent Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1109615108
... Read more »
Gomes Rodrigues, H., Marangoni, P., Sumbera, R., Tafforeau, P., Wendelen, W., & Viriot, L. (2011) Continuous dental replacement in a hyper-chisel tooth digging rodent. Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.1109615108
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