Competitive Dominance Pt. II

Last week, Wetland Wednesday focused on dominant species in wetlands and conditions that contribute to competition. Last week we talked a lot about plants, but animals can be dominant in wetlands as well, for example the American Alligator (Alligator mississippiensis).

Alligators are one of the most recognizable predator species of swamp and marsh habitats, but they haven’t always been as numerous as they are now. Alligators were endangered as recently as 1987 due to human impacts, especially hunting. [1] Since their conservation proved so effective, they are no longer on the endangered species list, but instead are now “of least concern”. It is impressive to see such a strong recovery for an endangered species, and their recovery was successful for many reasons, including their lack of strong competitors. Very few animals compare in size or bite strength. As apex predators, they have essentially free reign over other species when they reach maturity, although there is some competition between individual alligators. Productivity in swamps and marshes is extremely high compared to other habitats, so there is plenty of food to go around, but they still compete with birds of prey and other large aquatic animals like alligator gar and alligator snapping turtles (those names probably aren’t coincidental…).

As we mentioned last week, dominant species are not always native. Invasive species like nutria, or coypu, often out-compete native muskrats for similar food sources and homes. Since nutria are larger than muskrats, fewer species can prey on them. [2] Invasive species like nutria can disrupt communities of native species to the point of local extinction in some cases, especially in island ecosystems. [3] Not all introduced species are invasive; some do not significantly impact their new homes. Invasive species are detrimental by definition. Nutria were originally introduced by humans, which means their dominance over native muskrats is a byproduct of human activity. Similarly, zebra mussels and apple snails were introduced by humans and out-compete native species in coastal Louisiana.

Many species face the threat of population decline due to human activity, whether directly or indirectly. In a way, nearly all species on the planet are in competition with humans for food, territory, etc. or compete against one another to survive amid human impacts like climate change. Humans have done a great job altering landscapes to become livable for us, but those landscapes aren’t always good for native species. This kind of disruption has consequences to our own safety, however. Degradation of coastal marshes in Louisiana has been a consequence of human activity, and the risk of lowered wetland protection from storms poses a threat to our settlements. Since we have invested so much in where we live, it is in our best interest to reverse some of the damage we have done to those areas. CWPPRA is dedicated to coastal restoration because it is a responsibility we owe to both the environments we have disrupted and our communities that have come to depend on these environments.

[1] http://www.endangered.org/animal/american-alligator/

[2] https://www.aphis.usda.gov/publications/wildlife_damage/content/printable_version/fs_nutria10.pdf

[3] http://www.pacificinvasivesinitiative.org/site/pii/files/resources/publications/other/turning_the_tide.pdf

Featured image from http://www.louisianaherps.com/american-alligator-alligato.html

Competitive Dominance

Ecosystems around the world are in a constant state of competition as inhabitants impact each other, whether directly or indirectly. The theory of competition deals with interactions between populations within a defined range or habitat. [1] Individuals with more beneficial adaptations are more “fit” and will often out-compete others for resources like food, territory, or sunlight. Today, we will look at how one species can become dominant over its competitors in wetlands and what conditions might disrupt or completely tear down dominant species.

Some of our readers may immediately think of monoculture farming as a sort of dominance, and they would be correct. Although it is through artificial selection, crop species present some trait that Homo sapiens deems worthy of cultivating. For example, huge swaths of land in the United States have been clear-cut to make room for corn farms, cattle ranches, or even sugar cane farms. Maybe not to the same degree as artificial selection, natural selection can also produce habitats with dominant plants and animals. Coastal Louisiana’s wetlands are great examples of this. From Cypress swamps to Spartina marshes, wetlands are home to some hardy species who have adapted to harsh and variable conditions.

Wetlands go through cycles of drought and flood conditions, which can prove fatal for many species. [2] Wetland plants have adapted to survive the cycles and even exploit them. Cypress trees are a useful example because they don’t necessarily need flooded conditions to grow, they just need space and a little bit of protection when they are young. [3] Instead of becoming competitive on dry land with the thousands of other obligate dry land trees, cypress ancestors developed the ability to survive in water where few other plants competed. More information about their adaptations can be found in our second post about flood stress tolerance. In the salt marshes along our coast, smooth cordgrass (Spartina alterniflora) and other graminoids (grass-like species) dominate with their salt tolerance and fast reproduction. More about how cordgrass and black mangroves dominate other coastal species can be found in our first post about salt stress tolerance.

Within a species’ endemic (native) habitat, populations are limited by food availability, competition, and predation. However, species can move to non-native habitats that have plenty of food, less fit competitors, or little to no predation, in which case that species can become problematic. Invasive species are detrimental by definition and coastal Louisiana has several examples, which can be found in our invasive species article. Unfortunately, many invasive species move to new habitats with the help of humans, sometimes by accident and sometimes on purpose.

If you want to learn more about how human impact and other factors can change dominance structures, be on the lookout for Dominance pt. 2 next Wednesday!

[1] https://www.nature.com/scitable/knowledge/library/species-interactions-and-competition-102131429

[2] https://www.worldwildlife.org/habitats/wetlands

[3] https://www.arborday.org/trees/treeguide/treedetail.cfm?itemID=787

Featured Image from https://www.flickr.com/photos/9428166@N03/2686432231