Marine Ecology
Ecology
Ecology is the study of the distribution and abundance of species and the factors that affect them. These factors can be divided into two categories - abiotic and biotic. Alternatively, Marinebiology.org describes marine ecology as, "the study of populations, and interactions among organisms and the surrounding environment including their abiotic (non-living physical and chemical factors that affect the ability of organisms to survive and reproduce) and biotic factors (living things or the materials that directly or indirectly affect an organism in its environment)."Levels of Study
Ecology can be studied at a variety of levels. An ecologist can study a biome such as the "deep sea." A biome is a group of similar ecosystems with the same general abiotic factors and primary producers. An ecologist could also look at an ecosystem, which is more regionally specific than a biome. An ecosystem is a biological system consisting of all the living organisms in an area and the abiotic factors that affect them. A community is the biotic part of an ecosystem. It consists of all the populations of all the species in the same area. Finally, one could study ecology and the level of a single species or organism.
Organisms and the Environment
Organisms are individual living things. Despite their tremendous diversity, all organisms have the same basic needs: energy and matter. These must be obtained from the environment. Therefore, organisms are not closed systems. They depend on and are influenced by their environment. The environment includes two types of factors: abiotic and biotic.
Abiotic factors are the nonliving aspects of the environment. They include factors such as sunlight, soil, temperature, and water.
Biotic factors are the living aspects of the environment. They consist of other organisms, including members of the same and different species.
Limiting Factors
Some factors are density dependent (meaning the factor becomes stronger as a local population increases.) These density dependent factors can limit the growth of a single organism or a whole population of organisms, we call these limiting factors. Imagine an automobile factory, that loses a shipment of steering wheels. They have enough parts to make thousands of cars but only five steering wheels - how many cars do they make? For any organism or population of organisms there will be one or more "limiting factor" that limits growth.
The Flow of Energy
Energy enters ecosystems in the form of sunlight or chemical compounds. Some organisms use this energy to make food. Other organisms get energy by eating the food.
Producers
Producers are organisms that produce food for themselves and other organisms. They use energy and simple inorganic molecules to make organic compounds. The stability of producers is vital to ecosystems because all organisms need organic molecules. Producers are also called autotrophs. There are two basic types of autotrophs: photoautotrophs and chemoautotrophs. Photoautotrophs use energy from sunlight to make food by photosynthesis. They include plants, algae, and certain bacteria. Chemoautotrophs use energy from chemical compounds to make food by chemosynthesis. They include some bacteria and also archaea. Archaea are microorganisms that resemble bacteria.
Consumers
Consumers are organisms that depend on other organisms for food. They take in organic molecules by essentially “eating” other living things. They include all animals and fungi. (Fungi don't really “eat”; they absorb nutrients from other organisms.) They also include many bacteria and even a few plants, such as the pitcher plant. Consumers are also called heterotrophs.
Heterotrophs are classified by what they eat: Herbivores consume phytoplankton. They are a necessary link between producers and other consumers. Marine examples include zooplankton, some baleen whales, and small fish. Carnivores consume animals. Marine examples include tuna, salmon, many sharks, and killer whales.
Energy is transferred from producers to other organisms in a series of steps. These steps are known as trophic levels. The greatest "biomass" or mass of organisms, occurs at the lowest levels. Phytoplankton are far more abundant, collectively far more massive, than fish or marine mammals. For each level you go up, the amount of energy present in the level diminishes. When a Right Whale eats one ton of phytoplankton, it does not gain a ton in new mass. Most of the energy is lost to the system, in the form of movement and heat. Typically only about 10% of the energy is transfered into the next level. This loss of energy explains why there are rarely more than four trophic levels in a food chain or web. Sometimes there may be a fifth trophic level, but usually there’s not enough energy left to support any additional levels. (Image from Our Ocean Planet)
Keystone Species
Some higher level consumers are known as keystone species. A keystone species is one that plays an especially important role in its community. Major changes in the numbers of a keystone species affect the populations of many other species in the community. For example, some sea star species are keystone species in coral reef communities. The sea stars prey on mussels and sea urchins, which have no other natural predators. If sea stars were removed from a coral reef community, mussel and sea urchin populations would have explosive growth. This, in turn, would drive out most other species. In the end, the coral reef community would be destroyed.
Competition
Competition is a relationship between organisms that strive for the same resources in the same place. The resources might be food, water, or space. There are two different types of competition:
- Intraspecific competition occurs between members of the same species. For example, two male birds of the same species might compete for mates in the same area. This type of competition is a basic factor in natural selection. It leads to the evolution of better adaptations within a species.
- Interspecific competition occurs between members of different species. For example, predators of different species might compete for the same prey. Interspecific competition can lead to the extinction of one of the species competing. The species that is less well adapted may get fewer of the resources that both species need. As a result, members of that species are less likely to survive, and the species may go extinct. Interspecific competition will more often lead to greater specialization. Specialization occurs when competing species evolve different adaptations. For example, they may evolve adaptations that allow them to use different food sources.
The Niche
In the Begon et al. (1986) ecology text, niche is defined as, "the limits, for all important environmental features, within which individuals of a species can survive, grow and reproduce .” However, very few species have their ecosystem to themselves. They must share the ecosystem with other competing species all trying to consume the same resources.
The competitive exclusion principle — tells us that in a stable ecosystem, no two species are in direct competition with each other. So what happens when two or more species whose fundamental niches overlap occupy the same ecosystem? They work out an arrangement which we call "resource partitioning." This means that they jostle around until each species has reduced its niche size until there is no competition. The result is that, in a real ecosystem, a population is almost always utilizing only a part of the niche (the realized niche) they could have used if they were the only species in the ecosystem — so they are using only part of their fundamental niche. An example of this can be seen below in the work of Joseph Connell with two species of barnacle.
Symbiotic Relationships
Not all relationships in an ecosystem are competative. Symbiosis is a close relationship between two species in which at least one species benefits. For the other species, the relationship may be positive, negative, or neutral. There are three basic types of symbiosis: mutualism, commensalism, and parasitism.
- Mutualism is a symbiotic relationship in which both species benefit. An example of mutualism involves goby fish and shrimp. The nearly blind shrimp and the fish spend most of their time together. The shrimp maintains a burrow in the sand in which both the fish and shrimp live. When a predator comes near, the fish touches the shrimp with its tail as a warning. Then, both fish and shrimp retreat to the burrow until the predator is gone. From their relationship, the shrimp gets a warning of approaching danger. The fish gets a safe retreat and a place to lay its eggs.
- Commensalism is a symbiotic relationship in which one species benefits while the other species is not affected. One species typically uses the other for a purpose other than food. For example, hermit crabs use the shells of dead snails for homes. At no cost to the snail, the hermit crab has obtained a free house.
- Parasitism is a symbiotic relationship in which one species (the parasite) benefits while the other species (the host) is harmed. Most marine species are hosts to one or more parasites. Some parasites live on the surface of their host. Others live inside their host. They may enter the host through a break in the skin or in food or water. For example, tapeworms are parasites of many fish species, including wild Alaskan salmon. If you like salmon sushie, be sure its been well frozen before you eat it.
Questions to Research:
- Read the article,"Bering Sea Ecosystem Responding to Changes in Arctic Climate." Describe how abiotic changes in the Arctic ecosystem are leading to changes in the distribution and abundance of the species that live there.
- Click on the link for "Marine Zonation in intertidal communities ". Explain how different abiotic conditions like moisture, salinity, water movement, and temperature can affect what lives in different zones of the intertidal community.
- Life is controlled by the limiting nutrient. Read the blog post and describe what nutrient limits life for most of the ocean.
- Read the section from the reading above labeled "The Niche." Examine the picture (and the caption that goes with it) in that section. Describe what you think would happen if he had instead removed the chthamalus barnacles?
- Click on the link "Marine Food Webs" . What are the four dominant primary producers in the ocean. How are these organisms different from the plants that are primary producers on land.
- As humans have over-fished many of the larger fish in the ocean, they have begun to do so what some ecologist call - "fishing down the foodweb." Describe how this can cause some nasty ecological consiquences.
- Compare and contrast the evolutionary effects of intraspecific and interspecific competition. You might use examples in your comparison.
- Read "Marine Symbiosis," after reading provide one example for each type of symbiosis.
- Go to the Blue Planet's, "Webs of Life" After going through all five tasks, describe the transfer of energy from the primary producer level up through the top predators."
- What is a keystone species? Look up the sea otter and describe how they fit the definition as a keystone species.