Dimorphism: As they age, sex will become more apparent, as females can grow to be over twice the size of the males. Females grow to be 18-27cm (7-10.6in) long while males only grow to 9-16cm (4-6in). Map turtles are unusual in that they display differences between the sexes, not only in appearance but also in behaviour. Different sexes of map turtle occupy different niches, or perform different roles in their environment, making use of different resources. Females primarily feed on hard shelled invertebrates such as snails, mussels and crayfish while males, being smaller, tend to feed more on aquatic insects and smaller crayfish. This way, map turtles can still have a large population even when one resource becomes scarce, with little intraspecific competition.
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Invasive Species Control: Map turtles can be hugely beneficial at subduing invasive species. One species in particular; the zebra mussel has been found to make up roughly 36% of the female map turtles’ diet in Ontario. Zebra mussels were originally introduced from Eastern Europe and have quickly colonized the Great Lakes Basin. Here, they have been found feeding on much of the plankton that small fish depend on for food. One zebra mussel is capable of filtering up to on litre of water per day which, with a large population, can remove huge amounts of plankton from a given environment. They can also be problematic for recreational activities, such as swimming, as their sharp shells can cut people’s feet. Luckily, by feeding largely on these invasive species, map turtles can help protect waterways both for human use and for the local ecosystem.
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Conservation: Collisions with motor boats are one of the major factors leading to the decline of northern map turtles in Ontario. Northern map turtles occupy open water and can often be found just below the waters surface. Here, they can easily be hit by the propellers of many boats, in some areas up to 28.6% of the larger female turtles were found to have boat related injuries. These were only the ones found alive and it’s believed that many parish every year due to frequent use of motor boats. Basking map turtles are also effected by boats, in spring, when they bask more frequently, being routinely scared into the water by boats can reduce their metabolic rate by up to 7.8%. This is especially problematic in cold weather then they depend on the heat from the sun for energy. How can one avoid harming these turtles? By not using motor boats in environmentally sensitive areas and by being cautious when boating in the shallows, as in summer, map turtles prefer water no deeper than 2.5m (~8ft).
Sources:
Bulté, Grégory, and Gabriel Blouin-Demers. "Northern Map Turtles (Graptemys geographica) Derive Energy from the Pelagic Pathway through Predation on Zebra Mussels (Dreissena polymorpha)." Research Gate, Freshwater Biology, Mar. 2008, www.researchgate.net/publication/227720380_Northern_map_turtles_Graptemys_geographica_derive_energy_from_the_pelagic_pathway_through_predation_on_zebra_mussels_Dreissena_polymorpha?fbclid=IwAR. Accessed 16 Nov. 2021. Jain-Schlaepfer, Sofia M., et al. "Do Boating and Basking Mix? The Effect of Basking Disturbances by Motorboats on the Body Temperature and Energy Budget of the Northern Map Turtle." Wiley Online Library, Aquatic Conservation: Marine and Freshwater Ecosystems, 19 Sept. 2016, onlinelibrary.wiley.com/doi/abs/10.1002/aqc.2693. Accessed 16 Nov. 2021. "Northern Map Turtle Graptemys geographica." Virginia Herpetological Society, 2021, www.virginiaherpetologicalsociety.com/reptiles/turtles/northern-map-turtle/northern_map_turtle.php. Accessed 16 Nov. 2021. "Northern Map Turtle." Ontario Nature, 2021, ontarionature.org/programs/community-science/reptile-amphibian-atlas/northern-map-turtle/. Accessed 16 Nov. 2021. "Zebra Mussel." Nature Conservancy of Canada, 2020, www.natureconservancy.ca/en/what-we-do/resource-centre/invasive-species/zebra-mussel.html?fbclid=IwAR1pjWgaSHCu1wPnb-htXn8zT4ntwCdsxEM3xrVHnCNPf0GNnkoI-CmcQsI. Accessed 16 Nov. 2021. |