User:Bellisario.4/sandbox

Changes up though 12-4-14 After posting my edits, WolfmanSF took a lot of my additions down within a day. They took down my added section of "Threats to Gigantism". They're reasons were that it was basically saying naive insular species are susceptible to extinction. They also reworded my section of territorialism. They moved my section on island size effect and claimed my addition of a predisposition to large size was redundant since they already mentioned the island effect. However, to the casual reader, I think it would be good to include a simple explanation of the island effect. They also got rid of my section of "Additional Studies" because it "wasn't normal" to list off individual studies. However, I think they could be beneficial for evidence to the casual reader because most likely they will not want to look at a scientific journal and analyze it themselves if they are provided a brief summary in the article itself.

Changes to Island Gigantism Article

1. Addition of 'Threats to Gigantism' section: Since organisms showing traits of gigantism are usually left unchecked in size due to a lack of change in both the environment or the kinds of species on the island, it also means that they have a high chance of being wiped out if there was an introduction of a new species or new environmental condition that would directly compromise them. That is why giants are usually quite rare, as any sort of upset in the ecosystem could completely kill them off. [5]

2. Territorialism as a cause for gigantism: Another possible cause of island gigantism could be territorialism in certain species. A study on Anaho Island in Nevada determined that species that were more territorial tended to be larger than those that were not. Traits that bolster territorialism will be selected for if this quality gives an advantage to the organism, and usually this means the organism will be larger to be more intimidating to other species on the island. This, accompanied with the relatively shallow gene pool of the island population, means that the insular species will evolve at a faster rate towards a giant size. [5]

3. Island Size and Gigantism: Island size also plays a role in determining the effects of gigantism. Smaller islands generally accelerate the rate of growth in organisms, and extremes in sizes are usually found on smaller islands.

4. Predisposition to large size: Because larger individuals of a certain species are able to make the journey from the mainland to an island, their offspring and descendants will already be predisposed to have genes that code for larger sizes. This sets a firm foundation for large sized animals on an island to begin with, and the environment and other species determine what happens to their size from there.

5. Addition of a "Studies on Gigantism" section: A study in Scandinavia on nine-spines sticklebacks showed that when groups of these animals were isolated from predators, they were able to grow larger and live longer than their non-isolated counterparts. It should be noted that those groups most isolated (i.e. the ones in ponds as opposed to lakes and the sea), showed the most change in size. [8]

Another study conducted on the Canary Islands with different types of lizards found that both G. stehlini and G. simonyi had a reduction in overall size that could have possibly been from the introduction of humans and domestic animals to their natural environment. This example has its roots in the resource availability hypothesis and in predator-prey relations, and supports the claim that removal of constraints allows organisms to grow past their usual size. [9]

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A Closer Look at the Evolutionary Enigma of Island Gigantism

The concept of island gigantism has fascinated many over the years. With exotic animals such as the giant tortoises of the Galapagos Islands, the infamous Komodo dragon, and even extinct species such as Haast’s eagle and the moa, it’s hard not to wonder just what exactly made these species so huge in the first place. Many evolutionary biologists have conducted studies to uncover the mechanisms behind this enigma, and the results have been quite interesting. One major explanation is that while living on an island, animals without natural predators are able to grow larger without their size being kept in check. Another hypothesis is that there could be direct fitness benefits to the animals, such as with the well-known giant tortoise, which ensures the evoloution paper rough draft.docxtrend of gigantism is passed down from parent to offspring. At any rate, the topic of island gigantism is an integral part to the study of evolution as it helps to provide explanations as to why certain animals look and live the way they do, and shows just how strong of a force evolution and natural selection can be.

Perhaps what most people think of when presented with the word island in an evolutionary context is the island rule, which simply states that larger animals on an island become dwarfed, and smaller ones become bigger. But if this is a rule, then what about the studies that say that larger animals that migrate to an island continue to grow larger? The myth that all animals follow the traditional island rule needs to be busted. In fact, a study by Shai Meiri found direct evidence to counter this statement. In a study that utilized the mean snout-vent length of island lizards as an index for body size, they discovered that large island lizards do in fact grow larger while smaller lizards in turn grow smaller, thus directly conflicting with the general statement of the island rule (Meiri. 2011). However, some of the same thought processes as to what causes gigantism can still be traced back to the island rule, which deals with resource availability and the presence of a natural predator in close quarters with the species in question. Other studies go on to explain just how these particular forces can play a role in organism size on islands. In order for a species to exhibit characteristics of island gigantism, the organism has to physically get to the island in the first place. Which of these animals tend to make it to these islands? Studies suggest that the largest and the strongest of a certain population are able to make the journey, thus predisposing the new island population to be a large size in the first place. However, if on the island there is a lack of predators or competition both within a species and between other species that leave the new population unchecked in terms of growth, that is when evidence of evolutionary gigantism starts to show. One study focused on nine-spined sticklebacks from Scandinavia, which were isolated from other fish and when allowed to grow unchecked, they grew to almost double their size. They tended to live longer and had increased growth rates (Gabor et al. 2009). While genetics did appear to have a role in this, the main factors seemed to be a lack of predators and a lack of interspecific competition. It is also important to point out that the fish isolated in ponds, rather than lakes or oceans, grew the most. As a pond can be thought of as an inverse of an island, it adds great value to the argument that limited predators and interspecific competition can play a big role in the evolution of larger sizes in island organisms.

On a similar note, another study concluded that a lack of mammalian predators on an island allows for higher growth rates in island birds and reptiles (Meiri et al. 2011). Since these animals do not have to worry about being small and agile in order to find food and to escape predators, there is nothing stopping them from evolving into a larger size over the years. However, if a new species is introduced to the island that preys upon these larger birds and reptiles, then the large size will not be beneficial, and natural selection will act to make the population a more optimal smaller size. This would function as one of the checks in making sure island species do not continue to grow even larger. Another study conducted on the Canary Islands with different types of lizards found that both G. stehlini and G. simonyi had a reduction in overall size that could have possibly been from the introduction of humans and domestic animals to their natural environment (Barahona et al. 1999). This example has its roots in the resource availability hypothesis and in predator-prey relations. Severe outcomes of these particular situations, in which a new predator is introduced into the ecosystem and/or extreme environmental disruptions occur, are discussed later on.

One study conducted on Nevada’s Anaho Island chose to explore how territorialism contributed to organism size in island populations. Their results supported the resource availability hypothesis, which essentially states that an organism can only grow as much as its resources allow. What they saw was that the species that were more territorial were on average larger than those who were not, since the non-territorial animals were reduced in size to cope with the lack of resources (Feldman et al. 2013). Traits that promote successful territorialism, including a larger, more intimidating size, could quite possibly contribute to an overall increase in size in the organism, and given that the gene pool is already shallow among island organisms, the high number of individuals with more territorial tendencies coupled with larger sizes will push the population towards a “giant” size. This behavioral look at evolution gives a slightly different take on possible factors contributing to island gigantism.

Just as organisms with reduced resources tend to shrink in size, some of the species affected by gigantism can use their large size to their advantage during times of lower resources. In a study concerning island tortoises, the scientists concluded that larger sizes in oceanic island chelonians could help out when conditions became unfavorable, a common problem their island environment faces (Alfaro et al. 2011). These conditions ranged from inclement weather to low levels of food. What they saw was that larger sizes correlated directly with increased fasting ability, which would certainly help the longevity of these chelonians when faced with environmental strife. Again, we see natural selection at work here, as the tortoises that can survive these environments are the ones who have the ability to get through the adverse conditions, and if the ones that can make it are of the larger variety, we will see the chelonians at the very least maintain their current size, if not continue to grow larger.

In a more mathematical approach, biologists Ido Filin and Yaron Ziv focused on finding the rates associated with island gigantism. In a series of equations using calculus, they found that: a) the direction of the body mass change depends on the sign of the allometric exponent of dispersability, b) the smaller the island, the faster the change in body mass, and c) organisms show extremes in size more often on smaller islands versus larger ones (Filin and Ziv. 2004). What this is implying is that the more confined the area, the more size differences in species you will see.

(Lomolino, 2005) was able to summarize most of the above findings in his general study on insular vertebrates and their body sizes. Rather than focus on a particular species, Lomolino gathered information on many different types of island animals from resources already established to see if body sizes of island animals vary as a function of both the body size of the mainland population and the environmental conditions. He also comes to the conclusion that the resource-availability hypothesis is a major force in shaping body size of the island animals (i.e. that the more resources an animal has, the larger that it will become, and that animals with limited resources have to shrink in size to cope with this). He also references how larger size helps in colonizing ability in the first place which is why the organisms that grow larger tend to come from a lineage with larger sizes. Finally, he states that the system of giant organisms is fragile, and that an introduction of any new predator or environmental condition that the giant isn’t able to effectively deal with has the potential to cause massive waves of extinction (Lomolino. 2005). It can be inferred that this is why there aren’t too many extreme examples of animals affected by island gigantism today.

Island gigantism, although something that has puzzled many for centuries, is now becoming a topic of interest in the scientific community and even though more studies need to be conducted, it appears that there is a general consensus about some aspects behind it. If told in sequence, the “story” of island gigantism would most likely go like this: An organism that has better migrating ability (i.e. is larger) makes it to an island and begins to colonize it. That organism, if not faced with any environmental or interspecies stress, is able to grow without check and can surpass in size its mainland counterpart. This effect tends to also be correlated with the size of the island, as the smaller the island is, the faster a change will be seen. If these traits are beneficial, then the large size will be naturally selected for and will continue to be prevalent on the island. However, this system is a fragile one. The giants are susceptible to mass waves of extinction if a new environmental or interspecies stress is put on them. Although this “story” of island gigantism is an oversimplification, it does provide a groundwork that can be expounded upon in further studies, and with this new information in their arsenal, evolutionary biologists will be even closer to discovering all the parts of the history of life on Earth.

Literature Cited Meiri, S. 2007. Size Evolution in Island Lizards. Global Ecology and Biogeography 16.6: 702-08. Herczeg, G., A. Gonda, and J. Merilä. 2009. Evolution Of Gigantism In Nine-Spined Sticklebacks. Evolution 63.12: 3190-200. Jaffe, A. L., G. J. Slater, and M. E. Alfaro. 2011. The Evolution of Island Gigantism and Body Size Variation in Tortoises and Turtles. Biology Letters 7.4: 558-61. Meiri, S., P. Raia, and A. B. Phillimore. 2011. Slaying Dragons: Limited Evidence for Unusual Body Size Evolution on Islands. Journal of Biogeography 38.1: 89-100. Barahona, F., S. E. Evans, J. A. Mateo, M. Garcia-Marquez, and L. F. Lopez-Jurado. 2000. Endemism, Gigantism and Extinction in Island Lizards: The Genus Gallotia on the Canary Islands. Journal of Zoology 250.3: 373-88. Keehn, J. E., N. C. Nieto, C. R. Tracy, C. M. Gienger, and C. R. Feldman. 2013.         Evolution on a Desert Island: Body Size Divergence between the Reptiles of           Nevada's Anaho Island and the Mainland around Pyramid Lake. Journal of            Zoology 291.4: 269-78. Filin, I. and Y. Ziv. 2004. New Theory of Insular Evolution: Unifying the Loss of          Dispersability and Body-mass Change. Evolutionary Ecology Research 6: 115-24. Lomolino, M. V. 2005. Body Size Evolution in Insular Vertebrates: Generality of the Island Rule. Journal of Biogeography 32.10: 1683-699.

Article Edited

https://en.wikipedia.org/wiki/Island_gigantism

Suggestions on how Island Gigantism article could be improved

1. It is not mentioned in the article that increased size has its benefits in the animal being able to go long distances without food and water, such as with groups of land dwelling chelonians (e.g. Giant Tortoise). This could also be used as a start to a section called "possible benefits to gigantism, as most things in the article are about causes.

2. There is no mention of how territorialism is linked with gigantism. Some species need to be territorial to get their abundance of resources, and if extra defense mechanisms or behaviors are needed to do this, and this so happens to be linked to larger sizes, the population could evolve to push towards this bigger size.

3. The article doesn’t explain why larger animals can make it to populate a new island in the first place. It only says that they are better at colonizing islands. A lot of times, larger bodies are more helpful to animals for immigration to islands and, as a result, the populating species of the island is already larger than its mainland counterparts. As they continue to breed, generations later the organism has grown quite larger than its founding ancestors.

Sentence added and citation

There are several possible benefits animals affected by gigantism experience, including the ability to go long distances without food and water, as seen in the Giant Tortoise. If resources are limited, then the environment will select for those who are able to survive these conditions (the larger animals) and the population will continue to push towards the larger size.

Jaffe, A. L., G. J. Slater, and M. E. Alfaro. "The Evolution of Island Gigantism and Body Size Variation in Tortoises and Turtles." Biology Letters 7.4 (2011): 558-61. Web. 14 Sept. 2014. .

Josh Bellisario  	              Annotated Bibliography 			Tuesday 9:10

Jaffe, A. L., G. J. Slater, and M. E. Alfaro. "The Evolution of Island Gigantism and Body Size Variation in Tortoises and Turtles." Biology Letters 7.4 (2011): 558-61. Web. 14 Sept. 2014. .

This article quantitatively researched the correlation between habitat and organism size in the order of Chelonians. They predicted that body size was directly impacted by broad differences in habitat. Originally it was though that the large body size was a pre-adaptive trait that allowed the animals to colonize islands, but the continuation of the large size suggests that the large size was a favored trait, especially since island life can be unpredictable with changes in weather and other natural effects. The large size is beneficial if the Chelonian is faced with periods of fasting and can help it go long distances to get food and water. Sea turtles exhibited the largest size in the study, and this can be attributed to the fact that many sea turtles migrate across great distances, and the large size helps for their dispersal rates. Also, in the case of sea turtles, the larger size can be a good thing as it lowers the surface area to volume ratios, which helps it thrive in colder waters. All of these things are possible explanations as to why the members of Chelonians (specifically giant tortoises and sea turtles) have continued to adapt at a large size.

Herczeg, Gábor, Abigél Gonda, and Juha Merilä. "Evolution Of Gigantism In Nine-Spined Sticklebacks." Evolution 63.12 (2009): 3190-200. Web. 14 Sept. 2014.

A lot of times in a population, predation works to keep and animal smaller as it is easier to avoid a predator. When there isn’t a viable predator, however, the animal is free to grow larger and larger as it is unchecked. The point of the study was to see the evolution towards larger sizes of small fish on an island. P. Pungitius grew to almost double its original size when isolated from other fish communities. This was probably a result of longer longevity and increased growth rates. Pond fish grew faster and longer than lake or marine fish in certain parts of Scandinavia. There is a genetic basis to growth. Main causes are lack of predators and lack of interspecific competition add to this.

Keehn, J. E., N. C. Nieto, C. R. Tracy, C. M. Gienger, and C. R. Feldman. "Evolution on a Desert Island: Body Size Divergence between the Reptiles of Nevada's Anaho Island and the Mainland around Pyramid Lake." Journal of Zoology 291.4 (2013): 269-78. Web. 14 Sept. 2014.

The experimental data supports the resource availability hypothesis. Some species get their abundance of resources by being territorial, so extra defense mechanisms or behaviors could possibly coevolve along with the larger size in these particular organisms. The non-territorial species were shown to be significantly smaller on the island because of their need to reduce resource demands. Since the environment selects for these particular traits, the shallow gene pool will eventually keep pushing towards an extreme in size (for example, the territorial zebra tailed lizard) and over many generations, produce the animals we consider a result of “island gigantism”. Meiri, Shai, Pasquale Raia, and Albert B. Phillimore. "Slaying Dragons: Limited Evidence for Unusual Body Size Evolution on Islands." Journal of Biogeography 38.1 (2011): 89-100. Web. 14 Sept. 2014.

The lack of a mammalian predator on an island can be a possible explanation for the evolvement of large bodies in lizards, as instead of having to hide and forage for food, they become the dominant predator. This lack of a mammalian predator may also contribute to the flightless birds, since they do not have to make as quick escapes if not being chased by another animal. While it appears that island gigantism can apply to birds and reptiles (lizards), it seems that it cannot be applied to mammals.

Lomolino, Mark V. "Body Size Evolution in Insular Vertebrates: Generality of the Island Rule." Journal of Biogeography 32.10 (2005): 1683-699. Web. 14 Sept. 2014.

It is said that as islands become smaller and more isolated, there is a switch from interspecies pressures on organisms to a more intraspecies view. As resources become scarce, some animals will end up getting reduced in size to cope with the lack of resources, while others without natural predators will continue to grow. Island evolution occurs much quicker than mainland evolution due to the smaller population. In going with the idea that the large size helps to colonize islands, it is thought that the larger size goes hand in hand with immigration ability, so naturally the best immigrants are the ones with the larger size. Factor in generations of breeding and the result is an even larger organism than the beginning. The system of gigantism can be a fragile one though, because as soon as a foreign predator is introduced to the ecosystem, it is possible for massive waves of extinctions to happen as the now larger species has no way of hiding or defending itself from the new threat.