1. which of the conditions below would most likely allow two phytoplankton speci
ID: 155188 • Letter: 1
Question
1. which of the conditions below would most likely allow two phytoplankton species competing for the same resources in a chemostat to coexist for extended periods of time?
A. They have the same limiting nutrients.
B. They have the same reproductive rates.
C. They have the same death rates.
D. They have the same R* concentrations
2. Some investigators predict that the continued use of chemical fertilizers will have the long-term effect of changing nutrient ratios in aquatic systems. Specifically, they predict that the ratio of phosphorus to nitrogen will increase and the ratios of both nitrogen and phosphorus to silica will increase. Based on your experiments, which of the following would be the most likely outcome of this shift in nutrient ratios?
A. Diatoms will be favored over green algae and cyanobacteria, but insufficient information is provided to determine whether green algae or cyanobacteria will be favored over the other.
B. Green algae will be favored over cyanobacteria and diatoms, but insufficient information is provided to determine whether cyanobacteria or diatoms will be favored over the other.
C. Cyanobacteria will be favored over green algae and diatoms, but insufficient information is provided to determine whether green algae or diatoms will be favored over the other.
D. Diatoms will be the least favored, but insufficient information is provided to determine whether green algae or cyanobacteria will be favored over the other.
Explanation / Answer
Q. 1 Ans. D. They have the same R* concentrations
Why do so many phytoplankton species coexist while competing for a limited number of re -
sources in a nearly homogeneous environment? For example, open ocean and lake surface waters usually
contain the order of 1 to 10 dominant phytoplankton species together with many hundreds or more species
at very low concentrations. This high number of phytoplankton species appears at odds with the competitive
exclusion principle where the number of species coexisting at equilibrium is not expected to exceed the number of resources. For
phytoplankton, the resources can be viewed in terms of macro nutrients, trace metals and variations in the
light and temperature environment, such that if 2 phytoplankton species compete for the same re - source, the most successful competitor is the one surviving
on the minimum resource
Q. 2 Ans B.
In Moriches and Great South Bays (NY), for example, extremely dense populations of chlorophytes and cyanobacteria developed in waters fertilized by effluent
from adjacent duck farms. These blooms coincided with collapse of the oyster fishery.
Of primary importance from an ecological and public health perspective is the abundance of nutrients containing nitrogen (N) and phosphorus (P) that flow
into lakes, reservoirs, streams and rivers resulting in eutrophic conditions (USEPA). The N:P ratio often determines which algae genera are dominant, present
or absent in these nutrient-affected water bodies. Sources of the inorganic compounds that contain these elements include household laundry detergents,
commercial fertilizers used for lawns and agriculture, and stormwater runoff, along with organic pollution from sewage-related sources including leaky septic
tanks and livestock waste. Lakes and reservoirs that receive these sources of pollution periodically, or chronically, display high densities of algae growth
resulting in blooms of nuisance and/or toxin-producing genera.
Microscopic analysis of water samples collected from lakes, streams and other bodies determines the diversity and density of algal species and provides
potentially useful early warning signs of deteriorating conditions.
In lakes and reservoirs, symptoms of eutrophic situations are the late summer cyanobacteria surface blooms that occur when the water is thermally stratified,
sunlight intensity is high, there is a period of mild weather (low turbulence and calm winds) and the N:P ratio is low. Eutrophic lakes displaying blue-green
blooms are often shallow and support high densities of cyanobacteria that form unsightly and potentially toxic surface scums.
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