showed a strong degree of nestedness, the arboreal
marsupials were non-nested. In this case, their
explanation for the nestedness of the avifauna
invoked selective extinction as the dominant
process.
Table 5.2 provides an interesting classification of
nestedness patterns by Patterson (1990) using one
particular metric. Opinions have varied as to the
balance of explanatory power among the factors
generating nestedness (Pattterson and Atmar 1986;
Patterson 1990; Simberloff and Martin 1991; Cook
and Quinn 1995; Nores 1995), but Patterson’s con-
clusions appear to be broadly supported in a more
recent multimetric, multisystem analysis by Wright
et al. (1998), who have reaffirmed that land-bridge
archipelagos are typically strongly nested, and
immigration experiments least nested. Their
comparative analysis adds further support to the
argument that differential extinction is a powerful
force in producing nested structure, but also points
to the realization that different types of system may
be dancing to different tunes: sometimes immigra-
tion is dominant, sometimes extinction, sometimes
habitat nestedness. The relevance of nestedness
within conservation biogeography is examined in
Chapter 10.5.3 Successional island ecology: first elements
Consideration of nestedness in this chapter has
led to the point where questions concerning theSUCCESSIONAL ISLAND ECOLOGY: FIRST ELEMENTS 129Table 5.2Summary of significant nested subset structure (according to Patterson 1990), in
assemblages affected over various time periods by: mainly extinction; mainly colonization; or both
processes in concert. The study was based on the nestedness index,N, of Patterson and Atmar (1986),
which has been argued to be suboptimal for the analysis of systems affected by colonization (see
discussion in Cook and Quinn 1995).
Processes Nested Non-nested
Holocene changes
Extinction dominated Southern Rocky Mts mammals
New Zealand land-bridge birds
Baja land-bridge mammals
Baja land-bridge herptiles
Great Basin mammals
Colonization dominated Baja oceanic birds New Zealand oceanic birds
Baja oceanic mammals
Baja oceanic herptiles
Both processes Baja land-bridge birds
Great Basin birds
Long-term changes
Extinction dominated Australian wheat-belt mammals Australian wheat-belt lizards
North American park mammals
São Paulo sedentary birds
Bass Strait mammals
Colonization dominated All São Paulo birds
Both processes Penobscot Bay mammals
Short-term changes
Extinction dominated Mangrove area reduction
Colonization dominated Dispersing shrews and voles Breeding shrews and voles
Weeds of young lots Weeds of old lots
Both processes Mangrove defaunation