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1958 Niche partitioning by warbler birds
CHAPTER SIXTEEN
1958 Niche partitioning by warbler birds The concept MacArthur (1958) undertook a detailed study of the ecology of sympatric species of warbler birds. What made this research stand out is MacArthur’s ability to organize his observations around theories of competition and competitive exclusion.
The explanation MacArthur studied five species of congeneric warblers that seemed so similar that “.ecologists studying them have concluded that any differences in the species’ requirements must be quite obscure.” (MacArthur, 1958). However, MacArthur was guided by theories of competitive exclusion which dictated that if two or more species use the environment in the same way only one species will persist: “.to permit coexistence it seems necessary that each species, when very abundant, should inhibit its own further increase more than it inhibits the other’s” (MacArthur, 1958). MacArthur relies on published research and some indirect methods to first conclude that the five warbler populations are limited by densitydependent events and that in the case of the Cape May warbler the limiting resource was food. With this conclusion, MacArthur reasoned that any overlap in the use of limiting resources will lead to competition. To determine if such overlap occurs, MacAthur spent two summers (in 1956 and 1957) making detailed observations of the birds. To quantify his observations, he divided the volume of the spruce and fir trees where foraging and nesting took place into 16 intra-tree regions (such as trunk, inner branches, outer branches, etc.). These regions were divided by height above the ground and distance from the trunk. He then recorded how long each of the five species of warblers spent in specific foraging locations. These records showed that each species had a distinct part of the tree where most of its foraging efforts were focused. It also turned out that many of the nesting sites for each bird were close to their preferred foraging Conceptual Breakthroughs in Evolutionary Ecology ISBN: 978-0-12-816013-8 https://doi.org/10.1016/B978-0-12-816013-8.00016-8
© 2020 Elsevier Inc. All rights reserved.
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Conceptual Breakthroughs in Evolutionary Ecology
area. MacArthur also kept track of how long the birds flew between bouts of sitting and foraging. While in the trees some birds would hop from branch to branch while others would walk along a branch. MacArthur devised a method for recording the direction of movements while each bird was foraging so he could later compare these. MacArthur also observed differences in the duration of these flights and the types of movements made by birds while foraging. MacArthur concluded that “First, the observations show that there is every reason to believe that the birds behave in such a way as to be exposed to different kinds of food. They feed in different positions, indulge in hawking and hovering to different extents, move in different directions through the trees, vary from active to sluggish, and probably have the greatest need for food at different times corresponding to the different nesting dates” (MacArthur, 1958). While any two species showed some degree of overlap for some of these aspects of feeding, altogether MacArthur concluded that the warbler behaviors allowed them to avoid direct intense competition and ultimately coexist. MacArthur did not explicitly develop an evolutionary explanation for these observations. This research was certainly a starting point for later research on the evolution of resource partitioning (see Chapter 40).
Impact: 9 MacArthur’s work was an important collection of natural history guided by the impact of interspecific competition and the notion that species exclusion would be the outcome of severe competition. More formal theoretical research on partitioning resources to reduce levels of competition would be motivated by this work.
Reference MacArthur, R.H., 1958. Population ecology of some warblers of Northeastern coniferous forests. Ecology 39, 599e619.
1958 Niche partitioning by warbler birds The concept MacArthur (1958) undertook a detailed study of the ecology of sympatric species of warbler birds. What made this research stand out is MacArthur’s ability to organize his observations around theories of competition and competitive exclusion.
The explanation MacArthur studied five species of congeneric warblers that seemed so similar that “.ecologists studying them have concluded that any differences in the species’ requirements must be quite obscure.” (MacArthur, 1958). However, MacArthur was guided by theories of competitive exclusion which dictated that if two or more species use the environment in the same way only one species will persist: “.to permit coexistence it seems necessary that each species, when very abundant, should inhibit its own further increase more than it inhibits the other’s” (MacArthur, 1958). MacArthur relies on published research and some indirect methods to first conclude that the five warbler populations are limited by densitydependent events and that in the case of the Cape May warbler the limiting resource was food. With this conclusion, MacArthur reasoned that any overlap in the use of limiting resources will lead to competition. To determine if such overlap occurs, MacAthur spent two summers (in 1956 and 1957) making detailed observations of the birds. To quantify his observations, he divided the volume of the spruce and fir trees where foraging and nesting took place into 16 intra-tree regions (such as trunk, inner branches, outer branches, etc.). These regions were divided by height above the ground and distance from the trunk. He then recorded how long each of the five species of warblers spent in specific foraging locations. These records showed that each species had a distinct part of the tree where most of its foraging efforts were focused. It also turned out that many of the nesting sites for each bird were close to their preferred foraging Conceptual Breakthroughs in Evolutionary Ecology ISBN: 978-0-12-816013-8 https://doi.org/10.1016/B978-0-12-816013-8.00016-8
© 2020 Elsevier Inc. All rights reserved.
37
j
38
Conceptual Breakthroughs in Evolutionary Ecology
area. MacArthur also kept track of how long the birds flew between bouts of sitting and foraging. While in the trees some birds would hop from branch to branch while others would walk along a branch. MacArthur devised a method for recording the direction of movements while each bird was foraging so he could later compare these. MacArthur also observed differences in the duration of these flights and the types of movements made by birds while foraging. MacArthur concluded that “First, the observations show that there is every reason to believe that the birds behave in such a way as to be exposed to different kinds of food. They feed in different positions, indulge in hawking and hovering to different extents, move in different directions through the trees, vary from active to sluggish, and probably have the greatest need for food at different times corresponding to the different nesting dates” (MacArthur, 1958). While any two species showed some degree of overlap for some of these aspects of feeding, altogether MacArthur concluded that the warbler behaviors allowed them to avoid direct intense competition and ultimately coexist. MacArthur did not explicitly develop an evolutionary explanation for these observations. This research was certainly a starting point for later research on the evolution of resource partitioning (see Chapter 40).
Impact: 9 MacArthur’s work was an important collection of natural history guided by the impact of interspecific competition and the notion that species exclusion would be the outcome of severe competition. More formal theoretical research on partitioning resources to reduce levels of competition would be motivated by this work.
Reference MacArthur, R.H., 1958. Population ecology of some warblers of Northeastern coniferous forests. Ecology 39, 599e619.