Marine mammals and other organisms are constantly adapting and evolving, especially in light of current global climate change trends. These changes are ultimately forcing animals out of their historical niches, or the abiotic and biotic conditions of an environment that an organism needs to grow, survive and reproduce (Bowman et al. 2017). It is important to note these adaptations because species abundance can affect ecosystems as a whole, in either positive or negative ways. For example, the competitive exclusion principle states that no two species can coexist if they occupy the same niche because they will be competing for the same resources (Bowman et al. 2017). This principle is exemplifying how merely similar food choices can impact species distributions, and cause changes among communities, as those who are worse competitors eventually die off due to famine. The two main groups this paper will focus on are marine mammals, particularly those in the Carnivora family, and echinoderms. These two groups vary immensely, so analyzation of their differing characteristics and traits can reveal which group has a larger impact on their surrounding environment and which one can undergo changes without global concern.
Before noting these different organisms, it is important to identify what events or characteristics can lead to changes in niche distributions. There is a multitude of physical, chemical, or biological limiting factors that can cause niche separation, but there are specific ones that are most evident in marine organisms (Ausich 1980). The factors that contribute the most toward differences among communities include evolutionary change, geographic variation, and environmental variability. For example, an evolutionary change that results in a different food-size selection could force a marine organism to migrate to another niche to survive. In turn, geographic variation could be the result of communities of organisms being isolated from each other and eventually adapting traits that result in their inability to sexually reproduce with one another. Lastly, climate change is causing sea levels to rise, and the warming of oceans. These factors could cause marine mammals that rely on cold waters for survival to migrate toward the poles to sustain their way of life. Overall, there are a number of reasons why species have different niches overtime, but analyzing specific mammals’ feeding and locomotive tendencies can reveal what is causing these niche differences.
Within marine ecosystems, there are a multitude of organisms including echinoderms which are organisms that have radial symmetry, or legs around a central axis (Knott 2004). Echinoderms are subdivided into five categories: Asteroidea, Ophiuroidea, Holothuroidea, Echinoidea, and Crinoidea. These categories make up the current living echinoderm classes and each class consists of organisms that have different feeding patterns and locomotive habits. The first group, Asteroidea, contains one of the largest and most familiar classes: sea stars and starfish. These organisms are primarily found in the marine benthic community or the bottom of the ocean floor. These organisms have a star-shaped body, with a central disc at their center and multiple arms that radiate outwards. For movement, these organisms use their podia, or tube feet, to slowly crawl along the ocean floor. In turn, they focus on slow-moving prey, and once they grasp their food source, they evert their stomach and secrete an enzyme on their prey (Mulcrone 2005). The digestive juice in this enzyme eventually breaks down the tissue of their prey, and the sea stars then suck up their prey into their mouth, which is located on the underside of their body (Knott 2004). This way of feeding means this group of organisms has extremely restricted diets, so they live where their food lives. Any alterations among their prey mean that the Asteroidea have to migrate elsewhere to ensure their survival.
Another common group of echinoderms is the Ophiuroidea or brittle stars. These organisms have long and flexible arms, and movement is undergone by the rapid wriggling of their arms. These arms connect to their central disc and move by a system of muscles that link together by ball-and-socket joints (Hyman 1955). These organisms also eat small organisms that lie on the ocean floor, such as small crustaceans or worms, because they too live in marine benthic communities. They feed on these animals by extending their arms outwards, while one anchors to the ocean floor. This means that this group of organisms needs a niche with a stable ground so that they can adequately acquire prey. In contrast, the Holothuroidea organisms reflect very different traits and characteristics. This group consists of sea cucumbers that are found in nearly any environment but prefer tropical shallow-water coral reefs. These organisms feed on algae, small aquatic animals, or waste materials that they attain with the help of their tentacles surrounding their mouths. Their tube feet help them to move slowly through the ocean, but in response to predators, they can swim by flexing their bodies and inching along the seafloor (Hyman 1955). These diverse locomotive options enable this group of organisms to occupy a variety of niches and increase their chance of surviving.
Another group of echinoderms evident today is the Echinoidea, or sea urchins. These organisms’ bodies contain a shell that has spikes protruding from it, enabling urchins to camouflage or protect themselves from predators. Also, on the outside of their bodies are hundreds of transparent tubes that allow them to stick to the ocean floor or move at an extremely slow pace (Hyman 1955). To eat, these organisms use their five teeth to ingest algae or break down other foods they may consume, and their transparent tubes can also be useful in catching prey. The last group of echinoderms, the Crinoidea, includes sea lilies and feather stars. They differ from other echinoderms because of their structure, which resembles a plant, with their body and frondlike tentacles residing near the top and a stem stretching from their body to the ocean floor. These organisms are immobile and catch their prey by using their tentacles which have tube feet on the underside of them, enabling them to suction their prey and trap them (Hyman 1955). This group is one of the only echinoderms stationed in one place, so their habitat range is smaller than the other echinoderms.
Other than echinoderms, marine mammals also exhibit changes in their niches, especially mammals in the Carnivora family. This family consists of several species including Otariidae, Phocidae, Mustelidae, and Cetacea. The first family, Otariidae, contains eared seals otherwise known as sea lions. These mammals have large, slender bodies, with small cartilaginous external ears. Their flippers are long and paddle-like, but their hind flippers can be rotated under the animal when on land, which supports the body and assists in locomotion (Myers 2000). Sea lions primarily feed on fish and other small marine organisms, but these animals are not picky about their diets as long as it has meat. Also, it is important to note that these animals tend to hunt closer to shore because the further they migrate seawards, the higher the likelihood that they will become a meal for Killer Sharks or Whales. In comparison to this group are the Phocidae, or earless seals. This group includes the Northern fur seals that are distinguished by their absence of ears, larger sizes, and inability to use their hind limbs to move on land (Bajzak et al. 2013). This group spends more time at sea because they can dive deeper for longer periods of time, thus, increasing their choices when it comes to prey. They navigate through the water by using their fore flippers to steer and their hind ones to propel themselves forward. Their diet consists of small schooling fish and squids, and they do not chew their food but swallow it in small chunks. They feed primarily during the night because that’s when their prey is near the surface, so the sea lions can expel less energy in attempts to acquire their food.
Two other comparable Carnivora mammals fall under the Cetacea family: Mysticeti and Odontoceti. The first suborder, the Mysticeti, includes baleen whales or mammals without teeth. A commonly known organism within this category is the gray whale. This species’ ideal food source is small concentrations of planktonic animals that they ingest by opening their mouths and taking in the plankton and enormous amounts of water. Everything besides their food is then squeezed out the sides of their mouths, and the prey get caught on the baleen’s bristles (Woodward et al. 2006). To move, these whales use their flippers in a wing-like manner and propel themselves through the water. They also contain two blowholes, so they can only spend a mere 20 to 30 minutes underwater. In contrast, the Odontoceti, or toothed whales, live and eat differently. Within this suborder are bottlenose dolphins, which have short beaks and only one blowhole. They live in primarily tropical or temperate seas, and they feed on a variety of food including fish, squid, or crustaceans. Also, they do not chew their food but shake or rub them on the ocean floor until suitable-size pieces break off their prey (Shane et al. 1986). These mammals also often cooperate when hunting so their chances of attaining large amounts of food are minimal as they have to share whatever they attain with their local species members. To move, bottlenose dolphins use their fins to thrust them through the water, with a top dorsal fin whose function is to prevent the animal from “rolling”. Also, studies have been conducted that analyze the specific functions of the pectorals, and in 1986 Shane and associates found that this muscle helped bottlenose dolphins to rapidly stop and turn without flipping over. These two suborders differ based on whether they have teeth or not, and further analyzation reveals that this single differing morphological trait further impacts these species feeding patterns and ecological habitats.
Lastly, one of the most important species to note is sea otters, which are in the Mustelidae family. This species is important to note because they are a keystone species or a species that has a large impact on its ecosystem disproportionate to its abundance within the system (Bowman et al. 2017). Their diet consists of over 40 marine species, with a preference for sea urchins and clams, and they can dive up to 330 feet when foraging for food. They are also one of the only marine organisms to use tools, such as small rocks, to pry shellfish from rocks or hammer them open (Thometz 2016). Sea otters can swim by using their hind legs and tail, and some even “dog paddle” with all 4 feet when swimming or floating slowly. They prefer to reside in shallow waters, which is an issue since sea levels are slowly rising. This could be the driving factor behind sea otter niche differentiation, as they have to migrate to places where their food sources are abundant, and their habitats are secure.
Overall, the echinoderms and marine mammals exhibited very different feeding and locomotive strategies that result in their perceivably different niches. For the echinoderms, their shared location within the marine benthic community is why their body shapes are quite similar. However, their different means of acquiring food and moving between locations is why they live in benthic communities that differ in water temperature or depth. Their niches could further diverge if waters continue to warm, and species not able to adapt to these change could go extinct because of loss of prey or ideal habitats. In contrast, the marine mammals had very different habitats, with some even extending on land. Those with better fins or flippers remained primarily in the depths of the ocean, while those with better hind limbs migrated between marine and terrestrial environments. Niche differentiation between these organisms could be a result of not only climate change, but changes among competitive species. Species attempting to escape changes within their historical habitats could come in contact with the mentioned marine mammals and compete for prey or other resources. This interspecific competition, or competition between different species, could reduce the amount of available resources and cause the endangerment or extinction of species that rely on large quantities or specific types of food (Bowman et al. 2017). In this case, natural selection would determine what species survived and which ones went extinct due to inability to adapt and adjust to their changing ecosystem.
Ultimately, it is important to look at how species’ niches differ overtime because this information can reflect both the health and stability of an ecosystem. If species such as the sea otter are not as abundant as in the past, that could be a sign that an ecosystem is failing or will soon. These analyzations could be used to distinguish which areas would be most affected by reductions in specific organisms and whether human interference is needed. Ecosystems contain resources that many humans use and live off of, thus, reductions in the quality of these ecosystems can cause humans to suffer in result. This is just one reason it is important to observe changes among organisms’ niches and see how their distributional changes impact the surrounding community of organisms and people.