The Incredible, Shrinking Wild World and Why Size Matters

Candice Gaukel Andrews March 6, 2012 9
Galapagos iguana

Over the past century, tortoises, common toads, and iguanas have all started to reduce in size. ©John T. Andrews

Animals and plants are shrinking, and most scientists believe that global warming is the cause. Recently, researchers examined eighty-five species and found that 45 percent of them have been steadily decreasing in size from generation to generation. What’s more, this downward trend seems to coincide with an uptick in temperatures: Each degree of warming worldwide has been found to decrease the size of marine life by as much as 22 percent; and over the past century, tortoises, common toads, iguanas, red deer, and sheep in Scotland have all started to reduce in size.

But if a large number of species gets smaller at the same time, will our new, tinier world of plants and animals make much of a difference?

Getting smaller, but working harder

Plant life

In theory, plants should be growing bigger as more CO2 enters the atmosphere. But they, too, are shrinking. ©John T. Andrews

It’s been shown that rising CO2 levels in the atmosphere make ocean water more acidic, which causes plankton, corals, and mollusks to decrease in number. This lessens the amount of food available to species, which filters all the way up to the top of the food chain. Those reduced food supplies are likely to mean that animals at the apex — including humans — will grow to smaller sizes, have fewer offspring, and be more vulnerable to disease.

In theory, plants — which use CO2 for fuel — should be growing bigger as more carbon dioxide enters the atmosphere. But they, too are shrinking, likely because of droughts caused by climate change. One study examined 1,700 plant, insect, bird, and amphibian species and found that in order to deal with these changes, 80 percent of them were moving three miles closer to the poles every ten years, and 87 percent were breeding or flowering more than two days earlier each decade. Cold-blooded animals, particularly amphibians, were shown to be at the highest risk because having a smaller size meant a greater chance of their drying up in warmer temperatures.

It’s clear that as certain types of flora and fauna diminish or grow smaller in size, we’ll all have to work harder to procure food.

Bears barely there

The consequences of shrinking — linked to the problems of a warming planet — are seen most notably in polar bears.

A few years ago, BBC News reported on a study published in the Journal of Zoology that found that after studying three hundred polar bear skulls — which are an indicator of body size — those from the latter half of the twentieth century were 2 to 9 percent smaller than those from the early part of the century. The researchers believe the changes could be linked to an increase in pollution and the reduction in sea ice. Because the ice is melting, the bears have to use more energy to hunt. This increased effort needed to find food, they postulate, likely limits the animals’ growth.

Polar bear

Polar bears are getting smaller, probably as a result of a warming planet. ©Candice Gaukel Andrews

Not only that, but changes in skull shape were noted, too. While it’s not possible to unequivocally determine the cause (it could be related to a reduction in genetic diversity; hunting over the last century may have depleted the gene pool, leaving polar bears to suffer the effects of inbreeding), it might be that the shape changes are related to pollutants that have built up in the Arctic and in the polar bears’ bodies. In the past hundred years, concentrations of many man-made pollutants in the Arctic have significantly increased, including carbon and halogen compounds: fluorine, chlorine, bromine, or iodine. While some of these substances have been phased out, many are still being used in solvents, pesticides, refrigerants, adhesives, and coatings. In one researcher’s words, “Polar bears are one of the most polluted mammals on the globe.”

Female polar bears now weigh an average of 506 pounds, a full 143 pounds less than in 1980; and they measure almost nine inches smaller than before. As their weight has fallen, their health has suffered, impairing their ability to reproduce and have cubs that survive. And some scientists report that, in their desperation, polar bears are turning on each other. They deliberately hunt other bears, for example, by attacking females in their dens.

A few years ago, a U.S. government study predicted that global warming would cause the world’s polar bears to be gone by 2050. But this is now thought to be optimistic: The melting is accelerating so fast that many scientists believe the Arctic Ocean will be completely ice-free in summer by 2030. This lack of ice will mean smaller bears — if they are able to survive at all.

It should be pointed out, however, that fossil evidence from the Paleocene-Eocene Thermal Maximum fifty-five million years ago, when temperatures rose by 9 degrees Fahrenheit over a period of approximately twenty thousand years (carbon is now being released into the atmosphere at a rate ten times faster) and precipitation levels dropped 40 percent, shows that invertebrates like beetles, bees, and ants became 50 to 75 percent smaller. Other species ranging from single-celled diatoms to woodrats have also been shown to decrease in size during previous periods of global warming. Some would say that our current shrinking of animal species is just another natural period in Earth’s history.

Do you think this trend toward smaller species should sound an alarm? Or are we experiencing just another cyclical diminution of the world’s biota?

Here’s to finding your true places and natural habitats,



  1. Candice Gaukel Andrews March 15, 2012 at 11:04 am - Reply


    Thanks for writing. You might want to check out these stories:

    Best of luck,


  2. Claudia March 15, 2012 at 12:11 am - Reply

    Hello Candice,

    Could you provide me the specific scietific references that you mentioned. Specially the studies about the reduction in body size and polar bears. I am working with brown bears in a related topic and it would be great to have this information.

    great text!

  3. D. Winka March 8, 2012 at 1:27 pm - Reply

    Actually, I think the plants and animals have it right, too bad the human population is not taking notice and shrinking our size (i.e., number of people) living on this earth.

  4. David March 8, 2012 at 7:03 am - Reply

    This is important information from the link within the link above explaining that global warming is not necessarily associated with an evolutionary process, but with the habitat changes. Small deer are able to weather warmer winters and thereby bring down the average size of the population; acidification makes it harder to create larger shells. Warming probably hasn’t been going on long enough to materially affect mammalian phenotypes.

    “In some species such as the red deer in Europe, small individuals that might have died off during a severe winter are surviving the milder winters. That has led to smaller average sizes in deer populations, Sheridan said.

    Another effect of increasing carbon in the atmosphere is a rising level of acidification in the oceans. In more acidic water, corals, oysters and other shellfish have to work hard to build and maintain shells and thus don’t grow as large. That has effects up the food chain. Research has found examples of shrinking fish species in the Mediterranean, for example.

    There are examples of species that are increasing in size on average. According to Sheridan, many of those exceptions to the shrinking trend are from high latitudes, where global warming can increase growing or feeding seasons. This has happened before. According to Sheridan, archeology provides evidence of shrinking creatures in other warm periods. Eventually, smaller predators can subsist on smaller prey.”

    Evolutionary changes will occur over time as species adapt to the changed habitat. But the reason global warming is such a problem is that the change is happening faster than many species are able to adapt because of the time required for each new generation. Bacteria will probably do fine…

  5. D. Y. March 8, 2012 at 6:59 am - Reply

    Well beyond carry capacity. I attended a nature conservancy mtg regarding feeding the increasing human population and walked away feeling perturbed and befuddled that status quo will continue…then again it is not their job to curb the human population, just figure out how to feed it.

  6. Ellen March 7, 2012 at 12:56 pm - Reply

    Obviously the answer would be to just look back over time. And due to shrinking habitat and environment, where else is there to evolve to but smaller? Too many people!

  7. Frank Parker March 7, 2012 at 4:23 am - Reply

    Whether it is a natural or man-made trend the important thing IMHO is that we can, if we choose, take the necessary steps to reverse it.

  8. Travis March 6, 2012 at 6:05 pm - Reply

    A 150 pound shrink since 1980… horrifying.

  9. Bonnie Jean March 6, 2012 at 11:45 am - Reply

    I am afraid so.

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