Evolution, 4th Edition

340 CHAPTER 13

growing close to each other were more different in defense characteristics than

if they had been sampled at random [41]. The evolution of different defenses that

cause each species to be attacked by different enemies has contributed to the great

diversity of tree species in tropical forests [14, 37].

The diversity of species in a community also results from evolutionary diver-

gence that reduces competition among multiple species [66]. For example, among

sympatric members of the weasel family in both North America and Israel, the

spacing of the size of the canine teeth is more regular among species and sexes

than expected by chance. The canine teeth are used to kill prey, and the differences

in their size are thought to reflect differences in the average size of prey taken by

these carnivores (FIGURE 13.22) [17].

Futuyma Kirkpatrick Evolution, 4e

Sinauer Associates

Troutt Visual Services

Evolution4e_13.21.ai Date 11-29-2016

Low pH Dry

Ancestor

(in moist, moderate pH soil)

A B C

Landscape

(moderate pH throughout)

Wetter Drier

FIGURE 13.21 Factors that may affect phylogenetic relationships among the members

of an ecological community. The phylogeny depicts a hypothetical plant clade, the

ancestor of which was adapted to moist soils with intermediate pH. Among its current

descendants, one clade (A) has become adapted to, and is now found in, acidic soils,

and another (C) is associated with dry soils. In a landscape that includes wetter and drier

sites but lacks acidic soils, clade A is not found. Drier sites will generally have species in

clade C, and wetter sites species in clade B; the environment acts as a filter, resulting

in phylogenetic clustering by habitat. But variation among species in each clade leads

to stronger competition and exclusion between the closest relatives, so the closest

neighbors are phylogenetically overdispersed: they are not as closely related as might

be found in random samples of the species.

Futuyma Kirkpatrick Evolution, 4e

Sinauer Associates

Troutt Visual Services

Evolution4e_13.22.ai Date 11-30-2016

Au: Should (B) x-axis label be “Upper canine diameter (mm)” to match (A)?

Photos would look nice as silhouetted animals. Boxes are for possible layout only.

3 4 9

Upper canine diameter (mm)

65 87

Meles

meles

Herpestes

ichneumon

(A) (B)

Mellivora

capensis

Vormela

peregusna

Martes

foina

1.0 1.5 2.0

Upper canine diameter (mm)

2.5

M. frenata

M. nivalis

M. erminea

M. nivalis

Alaska

Minnesota

M. erminea

M. erminea

Vormela peregusna

Martes foina

Herpestes ichneumon

FIGURE 13.22 Size of the canine teeth differs among sympatric species of the weasel

family (Mustelidae), and between the sexes in each species, in (A) Alaska and Minnesota

and (B) Israel. In all sites, the spacing is more regular than would be expected at random.

These differences are thought to be adaptations to feeding on prey that differ in average

size. Herpestes ichneumon, the Egyptian mongoose, is a member of another family of

Carnivora but is ecologically similar to the mustelids. Vertical lines are means, horizontal

bars represent ( 1 standard deviation, and horizontal lines are range. (After [17].)

13_EVOL4E_CH13.indd 340 3/22/17 1:26 PM