10 Brown and Davidson 1977 Competition ants rodents

These were sized by passing them througha

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: e sized by passing them througha gradedseries of sieves (Tyler). Although ants take some seeds smaller than those utilized by rodents, there is extensive overlap (5). 0.1 0 .c 0.0 o U c 0.3 ANTS T0 LL o o0 o6 I X O o i It (D o V 0 (D F a co to r 0) o I - I o a) I - 0) - - 0 (D (0 I O t ) r) -I I (D01 (o a) , iq I t to .N I 0 O() - - N 0 I 0 rI N (o 0 o) K) rO I i i to .t A 0o a , "i 0 t i Seed Size (mm) Fig. 2. Patternsof species diversityof seed-eatingrodents (triangles) and ants (circles)inhabitating andy s soils in geographic gradients of precipitation and productivity. Correlation coefficients and significance levels for the fitted linear regressions are indicated. In the north-south gradient, where ant diversity does not vary significantly, rodentdiversity increases more rapidly with precipitation than in the east-west gradient, where the slopes for the two taxa aresimilar. 3 0 I(2 2 0 V) c I 0 E E 0 o 0 'o 6 'a5 E I z /A NORTH-SOUTH GRADIENT 5 A A 4 / / / / / RODENTS r=.85, P<.01 AA//A / / 3 A, // 2 0 0 100 200 300 Mean Annual Precipitation (mm) 881 Table 1. Summaryof the results of experimentsin which ants or rodentswere eliminatedfrom t plots and the unmanipulatedaxon was repeatedlycensused. Values in firstthree columnsare totals of all censuses. Ants were censused five times, and there were two replicates of each treatmentfor a total of ten comparisons.There were 25 comparisonsof rodent censuses: 13 censuses of the firstreplicatedset of plots (establishedin August 1973)and 12 censuses of the second set (establishedin December 1973). The last column gives the fraction of the comparisonsin which the experimentalcensus exceeded the control census. Total Taxon Ant colonies Rodents removed 543 Antsrelative Control removed - 318 Increase relative to control (%) Experi', mental > control 70.8 9/10 Rodents Number Biomass(kg) -144 - 5.12 122 4.13 *In five comparisons, the experimental equalled the control census. mental equalled the control census. columns for dense aggregates of seeds (8) showed the greatest numerical response to removal of rodents. This result suggests that exclusion of either rodents or ants enhanced the density of seeds available to the other taxon and corroborates competition. Comparative studies of associations of seed-eating rodent and ant species over geographic gradients of productivity suggest that competition between these two taxa affects the organization and function of desert ecosystems. In an east-west gradient, where latitude and environmental temperature were relatively constant, the numbers of coexisting species of both rodents and ants increased at almost identical rates (Fig. 2) with enhanced precipitation, a measure of productivity in arid regions (8, 9). In contrast, in a northsouth gradient, where declining environmental temperatures accompany greater mean rainfall at higher latitudes, there was no significant change in the number of ant species, but rodent species diversity increased more rapidly with productivity than in the east-west gradient (10). Although data are less complete, the same patterns characterize biomass and population densit...
View Full Document

This document was uploaded on 02/26/2014 for the course BIOLOGY 4368 at University of Houston.

Ask a homework question - tutors are online