THE NICHE CONCEPT & ETHNIC DIVERSITY(1).
IntroductionOne of the striking facts about contemporary society, and indeed of much of recorded history, is the division of the human species into distinct ethnic groups, whose interrelations are sometimes antagonistic and sometimes mutualistic.
While there are many interesting ways social scientists analyze this phenomenon, ecological theory may provide some additional insights.
This lecture approaches this topic as follows:
1. What is ecological niche theory? (brief summary).
2. How can we apply this theory to human ethnic diversity?.
3. Discussion of Swat case (Barth reading).
(2).
Niche TheoryNiche concept is central to modern ecological theory. In particular, niche is used to describe and analyze:
1. ways in which diff. species interact (including competition, resource partitioning, exclusion or coexistence);
2. why some species are rare and others abundant;
3. what determines geographical distribution of a given species;
4. what determines structure and stability of multi-species communities.
Term "niche" borrowed from church architecture, but in ecology it is not a spatial term like habitat or environment (though related to these).
What's the difference between the two concepts?
Habitat = "address" (environmental region or community inhabited by a population).
Niche = "profession" (way in which a population utilizes a habitat).
Though realizing that any population's niche is multi-dimensional in very complex ways, ecologists have often simplified analyses by considering one or two dimensions at a time (e.g., food resource niche).
Niche theory distinguishes between fundamental & realized niches:
• fundamental = all possible conditions under which population reproduces itself.
• realized niche = the actual niche exhibited in particular time & place.
Realized niche will almost always be a subset of ("smaller than") the fundamental niche, for various reasons; one important determinant of realized niche is presence or absence of different competitors.
Recall the definition of ecological competition (
competition lecture): presence of N1 has negative effect on growth rate of N2 because both populations utilize >1 of same limited (relative to demand) resources.
Obviously, the more limited resources two populations have in common (i.e., the more similar their niches are), the greater the impact of competition (all else being equal).
Consider an extreme case: Can 2 populations occupying the same resource niche coexist in the same environment?.
If 2 populations occupy same resource niche, then by definition they utilize all the same resources, and in the same manner.
Common sense tells us there are 3 possible outcomes to this situation:
1) share resources more or less equally (neither population changes niche).
2) one or both populations alters niche to reduce overlap (niche partitioning).
3) one population loses out completely (competitive exclusion).
Which outcome will occur? Answer from niche theory = 2 or 3, but not 1.
This somewhat counterintuitive finding given formal name of competitive exclusion principle (CEP).
CEP states that no two species can permanently occupy the same niche: either the niches will differ, or one will be excluded by the other (note: "excluded" here means replaced by differential population growth, not necessarily by fighting or territoriality).
Of course, 100% niche overlap is unlikely if not impossible; but such an extreme case is not necessary for competitive exclusion or other forms of niche change.
Much theory & research in ecology has focused on predicting what actually happens when there is niche overlap & competition: When does exclusion result, when coexistence? How much overlap is possible (a question treated by the "theory of limiting similarity")? How do environmental fluctuations affect this? Why are some species generalists, others specialists?.
Both possible responses to niche competition (competitive exclusion, and coexistence via reduction in niche overlap) are commonly observed, and their determinants and features have been studied by three means: lab experiments, field observations, and mathematical models or simulations.
Competitive exclusion is commonly observed when a species colonizes a habitat and out-competes indigenous species (probably due to absence of parasites and predators adapted to exploit the colonizer); (e.g., introduced placentals vs. indigenous marsupials in Australia).
Coexistence through niche partitioning is rarely observed directly, but can often be inferred from traces left by "the ghost of competition".
The typical means of doing so is to examine two populations that overlap spatially, but only partially, and then to compare the niche of each population in the area of overlap vs. the area of non-overlap.
In such a case, we often observe that in areas where competitors coexist, one or both have narrower niche range (e.g., diet breadth) than in areas where competitor is absent; this is because competition "forces" each competing population to specialize in those resources (or other niche dimensions) in which it has a competitive advantage, and conversely to "give up" on those in which the other population outcompetes it.
Thus, in absence of competitors a given species will often utilize a broader array of resources (closer to its fundamental niche) than it will in competitor's presence; this phenomenon is termed "competitive release".
When niche shift involves an evolutionary change in attributes ("characters") of competing populations, it is termed character displacement.
This is one of strongest kinds of evidence for role of competition in shaping niches, because it is unlikely to have alternative explanation.
A classic example of character displacement is change in length or shape of beaks in ecologically similar bird species that overlap geographically.
(3).
Human Niche DiversityTheories of niche (such as CEP & related models) primarily designed to analyze interactions between different species; but of course anthropologists are interested primarily in niche differences within a single species (Homo sapiens).
Because of cultural flexibility (and technology), humans are able to occupy extremely wide range of environments, and to adopt extremely wide range of niches.
Furthermore, specific human groups can become highly specialized in ways of utilizing env. (i.e., niche), and use the same env. in different ways (either sequentially, via cultural change/evolution, or simultaneously, as in Swat case analyzed by Barth--see below).
This has led many ecological anthropologists to argue that each human population or culture has its own distinctive niche.
However, different cultures are not the same as different species, since they can 1) interbreed, 2) borrow traits, or even 3) merge into single population.
These possibilities make it tricky to apply ecological niche theory to analysis of interaction between diff. human populations/cultures.
However, if we keep in mind that with humans we are talking about ecological populations and not necessarily reproductively isolated ones, niche theory can be useful for analyzing processes of diversification, competition, and cooperation among human societies.
In particular, can be a useful tool for analyzing cultural/ethnic diversity.
(4).
Ethnic Groups in Swat (Barth 1956)Barth's classic analysis of complex ethnic interaction in Northern Pakistan is good illustration of how niche theory can illuminate ethnic diversity.
(Fredrik Barth = renowned Norwegian social anthropologist; his interests include decision-making, ethnic differentiation and boundary maintenance, and sociocultural change, not ecological anthro per se).
Barth found 3 distinct ethnic groups living in river valleys and surrounding mountains. of Swat, N. Pakistan [see
TABLE and
MAP]
1) Kohistanis = seasonal agriculture + herding; oldest inhabitants.
2) Pathans = sedentary agriculturalists; entered area 1000-1600 AD.
3) Gujars = nomadic herders; entered in last 400 yrs.
Environment = very mountainous region (18,000 ft peaks) dissected by steep gorges in higher areas, broader alluvial valleys in lower areas.
Clearly the distribution of these 3 groups and their relations to each other cannot be described in terms of environments per se, nor can they be reduced to military/political strength (since the Pathan are clearly superior, but yet do not displace the Kohistani in the upland areas, etc.).
Complex patterns of ethnic distribution and interaction thus can be accounted for in terms of niche theory -- in particular, as results of a) competitive exclusion; and b) niche divergence to reduce overlap ---> coexistence...
Overall, the Swat example demonstrates:
1) complexity of human niche specialization.
2) ability for diff. cultures to co-exist via niche partitioning, as if they were different "species".
3) major reason for failure of env. determinism: two or more societies can inhabit same env. (at same time or sequentially) via differences in their niche (specialized ways of utilizing environment to make living).
Sources:
Source1 -
Source2.
