Differences In Niche Breadth Research Articles

The accumulation of deleterious mutations within the frozen niche variation hypothesis.

The frozen niche variation hypothesis proposes that asexual clones exploit a fraction of a total resource niche available to the sexual population from which they arise. Differences in niche breadth may allow a period of coexistence between a sexual population and the faster reproducing asexual clones. Here, we model the longer term threat to the persistence of the sexual population from an accumulation of clonal diversity, balanced by the cost to the asexual population resulting from a faster rate of accumulation of deleterious mutations. We use Monte-Carlo simulations to quantify the interaction of niche breadth with accumulating deleterious mutations. These two mechanisms may act synergistically to prevent the extinction of the sexual population, given: (1) sufficient genetic variation, and consequently niche breadth, in the sexual population; (2) a relatively slow rate of accumulation of genetic diversity in the clonal population; (3) synergistic epistasis in the accumulation of deleterious mutations.

Niche separation between the maned wolf (Chrysocyon brachyurus), the crab‐eating fox (Dusicyon thous) and the hoary fox (Dusicyon vetulus) in central Brazil

AbstractFour species of canids occur in the Cerrado of central Brazil. Three of them, the maned wolf Chrysocyon brachyurus, the crab‐eating fox Dusicyon thous and the hoary fox Dusicyon vetulus, were studied in Emas National Park between 1996 and 1999 to investigate niche separation. The diet of the three species was studied to understand niche breadth and degree of overlap. Habitat and activity patterns were used as second and third ecological parameters to define niche dimensions, and were estimated using camera‐trap data. The maned wolf is the largest species, weighing c. 21 kg, and is about three times larger than the crab‐eating fox and six times larger than the hoary fox. The major ecological differences between the three species were found in their food niche and habitat use, where crab‐eating fox presented higher differences from the hoary fox (Pianka's index of niche overlap (O) = 0.405). Despite differences in niche breadth, habitat use between the hoary fox and the maned wolf were more similar, explaining their larger overlap, in comparison with habitat use by the crab‐eating fox. Activity patterns among the species showed less divergence. The three species presented two activity peaks, one in the dusk–night period and another in the morning period. These data permit a better understanding of the ecological separation of the three Cerrado canids that enables their coexistence.

Resource partitioning among British and Irish mustelids

summary Seven species of mustelid carnivore live in the British Isles: weasel, stoat, mink, polecat, pine marten, badger and otter. Recent studies have hypothesized that coexistence of these species is facilitated by partitioning of resources according to prey size, particularly that of mammalian prey. This hypothesis has been supported by evidence of character displacement derived from even size ratios in skull length and canine diameter. To test whether this hypothesis is supported by empirical data, 98 studies of the diet of mustelids living in Great Britain and Ireland were analysed. Two main predictions were tested; that larger males ate larger prey than females and that larger species ate larger prey than smaller species. Male mustelids ate larger prey than females but there was no relationship between predator size and prey size, either for all species or when largely vermivorous badgers and piscivorous otters were excluded. There was no difference in dietary niche breadth between the sexes. Dietary niche breadth increased with body size in the assemblage excluding otters and badgers. The dietary niches of mustelids were partitioned along several axes, none of which was clearly related to prey size. The dietary niches of the five species living in Ireland (stoat, mink, pine marten, otter and badger) were more similar to one another in Ireland than in Great Britain and there was no difference in niche breadth between Irish and British mustelids. There was no evidence of competitive release in the diets of Irish mustelids. Resource partitioning according to prey size is apparent between the sexes within species, and this is probably correlated to sexual selection for size dimorphism. Empirical data do not, however, support a hypothesis of resource partitioning according to prey size between species. Interspecific aggression provides an alternative hypothesis explaining character displacement among mustelids.

Differences in daily mass gain between subordinate species are explained by differences in ecological plasticity

During winter, small birds in temperate zones increase their internal fat reserves to combat harsh environmental conditions and the drastic reduction in predictability of resource access. High fat reserves provide some benefits related to starvation-risk reduction, but also imply some costs related to increased predation risk. In general, subordinate species should increase their level of fat reserves in response to the unpredictability of resource access when in competition with dominants. However, the magnitude of such reserve increases could differ between subordinate species if opportunity of access to resources varies interspecifically in relation to differences in niche breadth due to differences in morphology. We tested the hypothesis that subordinate species (Parus cristatus) with decreased access to food will accumulate more fat than subordinate species (Parus ater) with greater opportunities. Results supported the prediction. We found that crested tit, the species with lower ecological plasticity and thus less access to food under competition, stores more fat daily than the coal tit, the species with higher ecological plasticity owing to its abiltiy to forage while upside down.

Species longevity as a function of niche breadth: Evidence from fossil crinoids

High-resolution stratigraphic and taxonomic data indicate that species longevities among Paleozoic (Mississippian) crinoids (Echinodermata) were affected by differences in niche breadth. A strong positive relationship exists between niche breadth, measured as the number of environments occupied by a species, and stratigraphic range. The robustness of this pattern is verified by a variety of rarefaction and statistical techniques confirming the long-held supposition that among animals ecological “generalists” have greater species longevities than ecological “specialists.” The results also support the hypothesis that specialist clades have higher species richness.

Niche Breadth and Life History Variation in a Hybrid Daphnia Complex

Laboratory life table experiments using multiple clones of Daphnia galeata, D. hyalina, and D. galeata x hyalina hybrids quantified differences in niche breadth among these taxa along a gradient of food carbon levels (0.2—2.0 mg/L). Two—way analysis of variance revealed significant main effects (i.e., species, food level) for all life history features examined, as well as significant species x food level interactions for several life history characters (e.g., age at first reproduction and intrinsic rate of increase, r). Nested analysis of variance revealed significant species level effects for all life history characters examined, as well as significant clone level effects for all characters except r. Overall, species level effects explained approximately twice the proportion of the total variance for individual traits when compared with clone level effects (means of 32.8 and 15.8%, respectively). Significant interspecific differences in breadth of response (i.e., niche breadth) were observed for estimates of r. D. galeata exhibited a significantly greater niche breadth across food treatments than D. hyalina; D. galeata x hyalina showed an intermediate response breadth, which was not significantly different from either parental species. The existence of considerable intraspecific (i.e., clonal) variation in several life history traits, implies that any interpretation of life history variation among members of hybrid species complexes may depend critically on the genetic (clonal) make—up of the populations examined. These results are discussed in reference to the coexistence of these taxa in nature.

Niche Pattern in a Forest‐Floor Small‐Mammal Fauna

This study examines the relationships among 4 small mammals species in 2nd—growth mesic forest on Walker Branch Watershed in eastern Tennessee, USA. Populations of Blarina brevicauda, Peromyscus leucopus, Ochrotomys nuttali and Tamias striatus were live—trapped on 9 0.36—ha grids during the summer of 1973. Eight measures of physical habitat structure were used in discriminant analysis of the microhabitats occupied by these 4 species. Three statistically significant discriminant functions were calculated. Each discriminant function is represented as an axis in a 3—dimensional discriminant space. These 3 axes are interpreted as vegetation type, vegetation structure and litter—soil surface characteristics. The positions of the species in the discriminant space characterize the microhabitat configurations of the species relative to the ecological properties attributed to the axes. Each species differs significantly from every other species on at least 1 axis. The observed species differences are conservative estimates of microhabitat (structural niche) segregation. We propose measures of niche position (i.e., exploitation speciality) and niche breadth based on the discriminant analysis. Species i is represented by a cloud of ni sample points in the discriminant space. Sample point j for species i lies the distance dij from the origin of the space. The average of these distances (°dj) represents the average "position" for species i relative to the origin. Because this origin represents the average of the microhabitats sampled on the watershed, and because the microhabitats actually occurring on the watershed are assumed to vary continuously, the likelihood of a species encountering favored microhabitat on Walker Branch decreases as °d increases. This ° is, thus, interpreted as an index of niche position relative to the average of the microhabitats sampled. Variability among the dij values for species i (vi) measures degree of specialization, a direct measure of niche breadth for species i. Our data indicate that °d and v are inversely related: breadth decreases as position becomes increasingly specialized. We incorporate measures of niche position, niche breadth and population abundance into an analysis of community "niche pattern." This niche pattern characterizes the 4 species as follows: Peromyscus is an abundant generalist, well—adapted to the watershed as a whole. Ochrotomys, the only other mouse, is a relatively rare specialist, poorly adapted to the watershed. Tamias occupies an intermediate position between Peromyscus and Ochrotomys, and exhibits intermediate abundance. Although we have little data for Blarina, this rare species appears to be poorly adapted to the watershed. Species differences in niche breadth appear to be determined more by the relative frequencies and carrying capacities of the species exploitation specialties than by the relative efficiencies with which the species exploit some critical limiting factor(s). Although we have no experimental evidence, the niche pattern observed for this community is consistent with an interference of competitive coexistence. The niche parameters of transient species which are infrequently encountered on Walker Branch are briefly discussed.