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Wetland Plant Population Lab – Understanding Niches
Introduction
Wetlands are most commonly defined by three main components: the presence of water for some or all of the year, unique wetland soils, and the presence of vegetation adapted to saturated soils. Wetlands are one of the most productive ecosystems on Earth. Wetlands cleanse polluted waters, prevent floods, protect shorelines and recharge groundwater aquifers. In addition, wetlands provide unique habitats to a wide range of living organisms. Historically, the San Francisco Bay had an abundance of wetlands. Most of these have been drained, filled, or diked resulting in the loss of critical habitat for a variety of flora and fauna. Approximately 90% of the historic tidal marsh in the San Francisco Bay has been lost.
One important factor affecting the distribution of organisms is their habitat. Habitat is the region where a plant or animal naturally lives and can normally be found. Many plants and animals occupy the same habitat. Because of this, they must share common resources. Niche is the role an organism plays in its community. A niche is part of the set of relationships between a species and its environment, and is much more than the habitat in which that species lives. A shark lives in oceans. That is its habitat. Part of the niche it occupies is that of predator. Other variables in a niche include territory, feeding habits, breeding habits, competition, and physiological constraints. Many species can coexist in a community because they occupy different niches. The fundamental niche of a species is the set of all environmental conditions that permit it to exist. A person cannot directly observe a fundamental niche because it is more of a concept, defined by an infinite number of variables. Even if a species has the potential to exist in a particular habitat, it may not. That portion of the fundamental niche that is actually occupied is called the realized niche. Competition and other species interactions often determine what portion of the fundamental niche becomes the realized niche. A species’ realized niche is consists of that species’ behavior, physiology, as well as its physical habitat. The spatial or physical components of a niche (i.e. soil moisture, elevation) define the species’ habitat.
Niche breadth is defined as the diversity of resources used by a species. It can be used to measure the distribution of species among habitats. Some organisms are able to live in almost any habitat (i.e. pests), while others are severely restricted in their resource use (i.e. koalas). Niche overlap is the extent to which species share the same resources. The competitive exclusion principle states that no two species can share exactly the same niche for very long, so species in a community that overlap to some extent must use at least some resources differently. For example, a great horned owl and a red-tailed hawk may share the same food source (rodents, rabbits, etc.) but hunt at different times of the day. Two plants may share the same soil type, but have different methods for pollination (wind, insects, etc.). If two species do overlap, natural selection will eventually result in either the coexistence of both species or the extinction/relocation of one of them.
The niche concept is abstract and impossible to measure exactly. However, ecologists have devised methods for determining fundamental versus realized niches, niche breadth and niche overlap. In order to help you understand the importance of habitat and niche, we will examine various species in our local wetland habitats. Specifically, we will determine how the species composition changes along an elevation gradient in a marsh.
Focus Questions
• What are the most common plant species present in a local salt marsh?
• What are some of the adaptations present in salt marsh plants that enable them to live in saturated, saline soils?
• How does the composition of plant species change along an elevation gradient within a local salt marsh?
• How do wetland plant adaptations relate to their fundamental and realized niches?
Procedure
1. With a piece of string, establish a transect within the marsh. Ideally, your transect should go gradually uphill. Have one member of your group place the string at the edge of the water. Another member should place the other end of the string at the highest elevation in the marsh.
2. Your first quadrant should be in the water (0 meters). Be careful not to lose your quadrant square.
3. Beginning near the water, place your quadrant on the ground at 1-meter intervals. For each quadrant, identify each of the plant species present, and list them in your data table. For each plant species, you should also determine the percentage of cover (the proportion of the entire quadrant that is covered by a particular plant). This should also be recorded in the appropriate spot on your data table.
4. Important: Each successive quadrant should be slightly higher than the last. In cases where there are dips in the marsh, skip over them so that your current quadrant is slightly higher than the last.
5. Continue this process until you are clearly out of the wetland and into upland habitat.
Graphs
1.Construct a single graph to illustrate elevation (quadrant #) versus % cover for each of the plant species present.
2.Your second graph should illustrate the average percent cover of each plant species identified within the marsh.
Analysis and Conclusion (Answer on binder paper)
1. Write a narrative description of your results. Which plant species were most common in the lower elevations of the marsh? Which plant species were present in the higher elevations of the marsh? Formulated an explanation for your results (Why are certain plant species more common in the marsh’s lower elevations?)
2. Identify and define the realized niches of cordgrass, pickleweed and salt grass.
3.Identify and describe major areas of niche overlap in the marsh.
4.Identify plants that have a broad niche and those that have a narrow niche. Explain how you determined whether or not a particular plant species had a broad or narrow niche.
5. What are some of the adaptations present in salt marsh plants that enable them to live in saturated, saline soils? How do wetland plant adaptations relate to their fundamental and realized niches?
6. Design a controlled experiment to determine the fundamental niche of pickleweed. Include the hypothesis that the experiment tests. Use the Experimental Design Outline as shown on p. 3 of the Environmental Science Guidelines for Experimental Research. Also include a step-by-step outline of your procedure.
The Effect of Marsh Elevation on Percent Cover of Various Plant Species
Plant Species / Percent / CoverQuadrant 0
(0 meters) / Quadrant 1
(1 meter) / Quadrant 2
(2 meters) / Quadrant 3
(3 meters) / Quadrant 4
(4 meters) / Quadrant 5
(5 meters) / Quadrant 6
(6 meters) / Quadrant 7
(7 meters)
Total Percent Coverage
(add columns)
The Effect of Marsh Elevation on Percent Cover of Various Plant Species
Plant Species / Percent / CoverQuadrant 8
(8 meters) / Quadrant 9
(9 meter) / Quadrant 10
(10 meters) / Quadrant 11
(11meters) / Quadrant 12
(12 meters) / Quadrant 13
(13 meters) / Average % Cover Within the Marsh
Total Percent Coverage
(add columns)