APS123 Papers and Practicals Flashcards
(38 cards)
What are the five species of warbler in the MacArthur paper?
- Cape May
- Myrtle (yellow-rumped)
- Black-throated green
- Blackburnian
- Bay-breasted
When and where are the warblers sometimes found together?
In the breeding season in relatively homogenous mature boreal forests.
What do the warblers mainly eat?
Insects
What was the aim of the study?
Determining the factors controlling the species’ abundances and preventing all but one from being exterminated by competition
What are the two types of events that regulate animal populations?
Density independent (e.g. storms, severe winters, some predation and some disease) Density dependent (for both occurence and strength), e.g. shortages of food and nesting holes
Small areas of habitat typical for one species may…
not contain that species if it is forced out by another species which uses this as a marginal habitat in a heterogeneous environment.
MacArthur thinks each species would have to be…
limited by a slightly different factor
There are four parts to the study. First, it showed that density…
dependent events play a large role in controlling the populations of the species
Secondly, a discussion of..
the general ecology of the species (food, feeding zones, feeding behaviour, territoriality, predators and mortality) is presented
Thirdly, the habits
of the different species in different seasons are compared to see what aspects of the general ecology are invariant and hence characteristic of the species
Fourth and finally, a wood-to-wood comparison of..
species abundances , relative to the important constituents of their niches as determined in the earlier stages, is presented
There tends to be an increase following a decrease, and vice versa, showing that population control is..
non-random
- unknown environmental cycle of approximately 2.5 years
MacArthur measured distances down from the top and outward from the trunk of individual …, … and … trees and divided them into zones,….
spruce, fir, pine,
recording feeding positions of the different warblers within each.
T3 indicated…
a bird feeding among abundant new needles and buds of the tip of a branch, between 20 and 30 feet from the top of the tree
M3 indicated..
feeding mostly among dead needles in the middle zone of a branch at the same height
B2 indicated…
a warbler feeding on the bare, lichen-covered base of a branch.
In all, … different positions were distinguished
16
- no competitive exclusion as different niches
The cape may stayed mostly…
toward the outside at the top
The Bay-breasted fed mostly around..
the middle interior
The myrtle (yellow-rumped) warbler moved..
from part to part more than the other two
The zones that contained… are blackened
50 percent of the birds’ feeding activity
Feeding habits differed too. For example…
the cape may warbler catches flying insects more often than the blackburnian and tends to move vertically rather than horizontally.
The black-throated green hovers much more than the bay-breasted.
Myrtle has most varied feeding habits.
MacArthur found evidence that food shortage…
limited the size of the warbler populations
Overall, macarthur concluded that..
“birds behave in such a way as to be exposed to different kinds of food”
- they also have somewhat different nesting times, and thus the times of their peak food requirements are not the same - partitioning a limiting resource (supply of insects) and in the process occupying different niches).
