Ecological & Natural Animal Features

  1. What is the main purpose of the paper? Why do the authors think it was important to do this study? When analyzing the results what was the author comparing?
  2. How did the authors collect the data?
  3. What is a ruminant species? What are the different aspects of diet they are studying? What were those major food classes?
  4. Looking at Figure 1, what is seen in terms of each ungulates diet? How did their diets change during the sampling period?
  5. Looking at Figure 3, what are some patterns that are seen in each animal’s selectivity? What is selective and non-selective grazing?
  6. What were the trends that surprised the author? What trends were in line with previous studies?
  7. If the pronghorn is so selective why does it consume more plant species while the bison is the least selective but has less plant species?
  8. How do the large ungulates compare to the smaller ones and how do the native ungulates compare to the domesticated ones?

Feeding Ecology and Niche Separation in Some Native and Domestic Ungulates on the Shortgrass Prairie Author(s): Charles C. Schwartz and James E. Ellis Source: Journal of Applied Ecology , Aug., 1981, Vol. 18, No. 2 (Aug., 1981), pp. 343-353 Published by: British Ecological Society Stable URL: JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Applied Ecology This content downloaded from on Sun, 21 Feb 2021 19:35:21 UTC All use subject to Journal ofApplied Ecology (1 9 8 1), 18, 3 4 3 -3 5 3 FEEDING ECOLOGY AND NICHE SEPARATION IN SOME NATIVE AND DOMESTIC UNGULATES ON THE SHORTGRASS PRAIRIE BY CHARLES C. SCHWARTZ* AND JAMES E. ELLIS Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, Colorado 80523 SUMMARY (1) Using the results of diet selection studies and two wild and two domestic species compare some aspects of ecology in relation to body size, the recent evolutionary h of the species and current forage conditions. (2) Food niche breadth and inter-species diet overlap seemed dependent upon recent evolutionary history as well as upon body size, but values were strongly influenced by forage quantity and quality. (3) Dietary selectivity appears especially sensitive to seasonal changes in forage quality, e.g. large as well as small animals pursued relatively selective strategies when forage conditions permitted, but body size and related nutritional-energetic demands appeared to set the limits where switches from selective to non-selective tactics took place. (4) Sensitivity to diet composition and quality increased with decreasing size except in the domestic sheep.

It is likely that anatomical-physiological adaptations, including a relatively large rumeno-reticulum allow domestic sheep to utilize more forage plant species and inhabit a wider variety of niches and ecosystems than most ungulates. Human selection has made the sheep food and habitat generalists despite their relatively small size. INTRODUCTION Sympatric ungulates tend to exploit their environments in different way mouth morphology, gut morphology and function and body size cause spe in diet, grazing behaviour and in grouping patterns. These divergent explo lead to differential habitat selection, grazing successions, contrasting soci ultimately determine ungulate community structure (Vesey-Fitzgerald 1960; Kleiber 1961; Lamprey 1963; Gwynne & Bell 1968; Hofmann 1968; Bell 1971; Hofmann & Stewart 1972; Jarman 1974; Ellis & Travis 1975; Janis 1976; Giesecke & Van Gylswyk 1975).

These generalities have derived largely from studies of African ungulates and have not often been evaluated for ungulates of other regions. In North America, bison (Bison bison) and pronghorn (Antilocapra americana) are native ungulates of the continental grasslands. During their long sympatric association compatible trophic strategies and adaptations to available forage have developed. Domestic cattle (Bos taurus) and sheep (Ovis aries) have been in North America for a much shorter time and so may be less well adapted to * Present address: Alaska Department of Fish and Game, P.O. Box 1809, Soldotna, Alaska 99669. Mailing address: James E. Ellis, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, Colorado 80523. 0021-8901/81/0800-0343 $02.00 (C 1981 Blackwell Scientific Publications 343 This content downloaded from on Sun, 21 Feb 2021 19:35:21 UTC All use subject to 344 Feeding ecology and niche separation available forage and to other ungulates, yet they are now the dominant grassland ungulates in North America and elsewhere. In this paper we have synthesized the results of several co-ordinated studies on diet selection, food habits and foraging behaviour in these two native and two domesticated ungulates (Peden et al. 1974; Rice, Dean & Ellis 1974; Ellis & Travis 1975; Peden 1976; Ellis et al. 1976; Schwartz & Nagy 1976; Schwartz, Mathews & Nagy 1976a; Schwartz, Nagy & Rice 1977; Dean et al. 1975; Kautz & Van Dyne 1978), and we analyse the results of these studies in the perspective of ungulate feeding ecology and forage niche separation. METHODS All studies were at the Pawnee Site, located on the USDA Science and Education Administration-Agricultural Research Central Plains Experimental Range in north-easte Colorado.

They formed part of the US/IBP Grassland Biome investigation. The vegetation of this region (shortgrass prairie) is dominated by blue grama (Bouteloua gracilis) and buffalograss (Buchloe dactyloides) and is described in detail by Klipple & Costello (1960) and Jameson (1969). The study pasture was grazed by cattle (one animal unit/12. 1 ha/for 6 months), from May to October. Tame, trained pronghorn (Schwartz, Nagy & Kerr 1976b) and oesophageally fistulated bison, cattle, and sheep (Peden et al. 1974) were used to determine botanical composition of ruminant diets. Sampling was done in late March, late April to early May, late June to early July, mid-August and mid-October. Details of sampling and of vegetative and chemical composition of ungulate diets are given in Peden et al. (1974), Peden (1976), Schwartz & Nagy (1976), and Kautz & Van Dyne (1978). Grazing behaviour is reported by Ellis & Travis (1975) and Schwartz et al. (1976a). The results reported here are analysed on the basis of five major food classes rather than on a plant species basis. Food habits were compared by the degree of diet overlap among the four ruminant species, (Morisita 1959; as modified by Horn 1966). This is an estimate of two species alpha (a) coefficients in the competition equations of MacArthur & Levins (1967). The overlap coefficient C. varies from 0, for completely distinct samples (no food categories in common), to 1, for indentical samples: S .2 E X1Y1 i= = X12 + E y, where S is the total number of plant groups and Xi and Yi are the proportion of the total diet of herbivore species X and Y taken from plant group i. Using the same overlap coefficient C., we calculated dietary selectivity expressed as the degree of overlap between forage class abundance in the pasture (Table 1) and food class in the diets (Table 2). Discussion: Ecological & Natural Animal Features

Values near 0 indicate a high degree of selectivity, while those near 1 show that food items were consumed in proportion to their abundance in the pasture (non-selective grazing) (Ellis et al. 1976). Diet diversity or niche breadth (B) was calculated following the method of MacArthur (1972) and Weins & Rotenberry (1979) as the inverse of Simpsons diversity measure (1949). This content downloaded from on Sun, 21 Feb 2021 19:35:21 UTC All use subject to C. C. SCHWARTZ AND J. E. ELLIS 345 TABLE 1. Herbage availability on a lightly grazed pasture at the Pawnee Site, May-October 1971 Herbage availability (kg/ha) (% total herbage) Plant group April-May June-July August October Warm season grass 361 (60-9) 783 (69.5) 520 (69-2) 392 Cool season grass 24 (4.0) 58 (5-1) 40 (5-3) 19 Grass subtotal 385 (64-9) 841 (74-6) 560 (74.5) 410 Warmseasonforb 14 (2-4) 83 (7-4) 38 (5.1) 70 Cool season forb 14 (2-4) 34 (3.00) 12 (1-6) 7 (68-4) (3-3) (71.7) 12.1) (1-2) Forb subtotal 38 (4-8) 117 (10-4) 50 (6-7) 77 (13-4) Shrub 180 (30-4) 169 (15.0) 141 (18-8) 86 (15.0) TABLE 2. Percent dry matter of plant groups in bison, diets collected from a lightly grazed pasture on the shortgrass prairie. Colorado, March to October 197 1* Percent dry weight Plant group March April-May June-July August October Bison Warm season grass 70 44 78 88 82 Cool season grass 28 54 15 7 17 Warm season forbs 0 1 7 5 1 Cool season forbs 0 1 1 0 0 Shrubs 0 0 0 0 0 Cattle Warm season grass 32 12 24 65 58 Cool season grass 44 67 46 8 28 Warm season forbs 4 2 22 27 9 Cool season forbs 0 1 7 0 0 Shrubs 21 15 1 0 5 Pronghorn Warm season grass 17 0 9 8 21 Cool season grass 65 37 0 0 50 Warm season forbs 17 41 75 92 29 Cool season forbs 1 22 16 0 0 Shrubs 0 0 0 0 0 Sheep Warm season grass 33 13 22 28 38 Cool season grass 7 50 19 4 31 Warm season forbs 4 8 38 68 28 Cool season forbs 0 1 14 0 0 Shrubs 57 27 3 0 2 * Data for bison, cattl from Schwartz & Nagy (1976). n B = I p2i 1=1 where pi is the relative biomass of the ith forage class in the diet. RESULTS The forage classes consumed by the ungulates in this study included warm-se cool-season (C3) grasses, warm- and cool-season forbs, and shrubs. The succule polyacantha is abundant in the area but was not eaten. The only abundant shrub is Artemesia frigida (fringed sagewort). Discussion: Ecological & Natural Animal Features

Table 1 shows the abundance of these various This content downloaded from on Sun, 21 Feb 2021 19:35:21 UTC All use subject to 346 Feeding ecology and niche separation forage classes in the pasture. Peak standing crop biomass of vegetation was reached during mid-growing season (June-July). Throughout the year, warm-season grasses were the most abundant forage class; forbs were the least abundant and most ephemeral but sometimes constituted large proportions of ungulate diets. Botanical composition of diets Diet composition varied among ungulates. Bison diets were dominated by warm-season grasses although cool-season grasses were also eaten at the beginning of the growing season (Table 2). Cattle (the other large ungulate) had a more varied diet including larger proportions (14-30%) of non-grass items (Fig. 1). Cattle ate some shrubs early in the year, and some forbs later, but grasses dominated their diets. Dietary proportions of warm- and cool-season grasses reflected plant phenology (Fig. 1). Pronghorn ate 63-92% forbs when these were available but relied mostly on coolseason grasses at other times. Like cattle, sheep consumed all forage classes; however, shrubs were only a major item early in the year. Forbs, cool-season grasses and warm- season grasses were eaten for much of the year (Fig. 1). Discussion: Ecological & Natural Animal Features

Botanical composition of diets is reported on a plant species basis by Peden et al. 1974, Schwartz & Nagy 1976, and Kautz & Van Dyne 1978. Chemical composition of diets To determine diet quality, dietary crude protein (CP), cell wall constituents (CWC) and dry matter digestibility (DMD) were analysed. Diet quality was generally greater (higher CP, lower CWC, higher DMD) for the small ungulates (pronghorn-sheep) than for the large ones (bison-cattle), (Fig. 2). Within size classes, diet quality was consistently higher for cattle than for bison. Pronghorn diets were higher in crude protein than sheep diets early in the sampling period, but the situation reversed by mid-growing season. (a) .00 80 (b) SF ……. SW 4 SF: 60 40CS aWS 20 ~i) 0 WSG 40,/.X. .. ..~.~.. .. .. .WF. *. .. .. .. .. .. /. <.////,/. . .. .,I/. ,./,.s/., /, / (C) (d) ~ ~ ~ ~ . . . . . . . . . . . . ,. . 100 /A——S——*—–s o————,_*.*………+S o~ / ////S/- / //…. – …————–/// _* . … ………..*h G C/ S …. sF …………….-..-….-.—60S / S. –*—-.*/5 ……………A.{ ,*. +*-*. .s 6 0 40 WSF~~~~~~~~~~~~~~~~~… …… ..W …… ….. …..r. ……. , …. 20 ,.. ………………………A ,,,,,,,, , ………………, , t~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ I. . . . . . . . . . ., ., . . . . . . . . . . . .,,,I ,- ………. .. . . . -M A M J J A S 0 M A M J J A S 0 FIG. 1. Botanical composition of diets as percentage dry weight of vegetation classes. Cross-hatched area = grasses, CSG = cool season grasses, WSG = warm season grasses, stippled area = forbs, CSF cool season forbs, WSF = warm season forbs, unshaded area = shrubs. a bison, b = cattle, c = pronghorn, and d = sheep. This content downloaded from on Sun, 21 Feb 2021 19:35:21 UTC All use subject to C. C. SCHWARTZ AND J. E. ELLIS 347 20 (a) O10 *../ \X O I l l l l l l l 100 -(b) 80- 070 – ***. .-a. . 60 – 100 – (c) 80 80 _ O 60 40 – – on7 I l lI March April May June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. FIG. 2. Comparisons between the percent (a) crude protein (CP), (b) cell-wall constituents (CWC) and (c) digestible dry matter (DMD) for diets of bison (-), cattle (—), pronghorn (.-*), and sheep (…. ). Data for bison and cattle, from Peden (1972: pp. 69-70, Tables 7 and 8). Data for pronghorn and sheep, from Schwartz et al. (1977). Alternately, sheep diets were higher in cell wall during the growing season but lower in the non-growing season (Fig. 2). Diet quality varied more for the small ungulates than for cattle and bison which maintained more constant diet quality and had parallel diet quality trends through the year. Dietary crude protein trends were similar for all ungulates; highest in May and dropping thereafter. DMD trends were generally similar for bison, cattle and pronghorn diets and to CP trends. Dietary CWC were uniform and similar for bison and cattle, but sheep and pronghorn CWC differed from this trend and from each other. Diet crude protein, cell wall constitutents and dry matter digestibility were significantly different for all ungulate species (Peden et al. 1974; Schwartz & Nagy 1976). Dietary selectivity Diet composition was compared with pasture forage class composition to obtain an estimate of dietary selectivity. This index indicates selective consumption of particular forages as opposed to consuming forages in proportion to their occurrence (non-selective This content downloaded from on Sun, 21 Feb 2021 19:35:21 UTC All use subject to 348 Feeding ecology and niche separation grazing) (Ellis et al. 1976). Low values indicate selective grazing; high values, non-selective grazing. The expected size-related trend in selectivity (Bell 1971; Hofmann 1968) was not complete. The largest ungulates (bison) were less selective than cattle; however sheep (the smallest at 25-35 kg) were always less selective than pronghorn (35-55 kg) and sometimes less selective than cattle (I 250-300 kg) (Fig. 3). High 0 – 0-2 – 0-Q4 *l * sN b – *.. . 0.8 March April May June July Aug. Sept. Oct. Nov. FIG. 3. Selectivity indices for diets of bison, cattle, pronghorn and sheep (symbols as in Fig. 2) Overlap calculations [Morisita (1959) as modified by Horn (1966)] compare the proportion of food items in the diet to availability in the pasture. Diet overlap Diet overlap was generally low between the native ungulates (Fig. 4). Non-overlap was nearly complete in August when bison consumed warm-season grasses and pronghorn warm-season forbs. Greatest overlap occurred early and late when pronghorn diets included 70-82% grasses (Table 2). “O – ( a) 0.8 – 0.4 – ‘a 0.2 0 0 1.0 (b) 2 a / /- _ ‘ Oa6_ Oa2 CMarch April May June July Aug. Sept. Oct. Nov. FIG. 4. Diet overlap calculations comparing (a) ungulate size classes (—, cattle-sheep; pronghorn-bison) and (b) native and domestic species (—, bison-cattle; -, pronghorn-sheep). The overlap measure was from Morisita (19~59) as modified by Horn (1966). This content downloaded from on Sun, 21 Feb 2021 19:35:21 UTC All use subject to C. C. SCHWARTZ AND J. E. ELLIS 349 Diet overlap was high for cattle and sheep averaging near 0.90 throughout. Both animals ate relatively diverse diets at all seasons (Fig. 1). No single plant group exceeded 70% of the diet at any time (Table 2). When compared by body size, diet overlap was relatively high, particularly at the end of the growing season for both large and small ungulates. For three of the four comparisons, overlap was low in July and August and high near the beginning and end of the sample period (Fig. 4). Diet niche breadth Pronghorn consumed more plant species (118) than sheep (42), cattle (66), or bison (43). Three, four and five plant species accounted for 65-75% of the diets of bison, cattle and sheep respectively, but 8-11 plant species had to be included to account for 67-75% of pronghorn diets .(Kautz & Van Dyne 1978). Discussion: Ecological & Natural Animal Features

Diet diversity values (Table 3) show that bison relied on not only the fewest plant species but also the fewest forage groups. Despite consuming a wide variety of plant species, pronghorn niche breadth, as measured by forage class diversity, was narrower than for cattle and sheep which consistently relied on a wider variety of forage classes (Table 2). The variance around these niche breadth values show that the small ungulates were adept at switching from one forage class to another over the season while bison were not; cattle were intermediate. TABLE 3. Ungulate dietary niche breadth, based on diet forage class diversity, Mar.-Oct. 1971 March April-May June-July August October X S Bison 1.70 1 98 1.60 1.28 1-43 1.60 0-267 Cattle 2-98 1-94 3-01 1.99 2-35 2.45 0.516 Pronghorn 2.08 2-83 1.68 1-17 2.64 2-08 0-683 Sheep 2-31 2-83 3-69 1.84 3-07 2-75 0-709 Grazing behaviour and habitat selection Pronghorn and cattle foraging patterns were compared for time spent grazing, grazing location and temporal patterns in grazing activity (Ellis & Travis 1975; Schwartz et al. 1976a). Time spent grazing was greater for cattle than for pronghorn. Pronghorn grazed at night more than cattle but both species reduced grazing activity at night. In 1972 time budgets were analysed for 24-h periods; pronghorns averaged 43.7% and cattle 47.5% time spent grazing. Discussion: Ecological & Natural Animal Features

In 1973 when analysed on a daylight-only basis, cattle averaged 62. 1% and pronghorn 52 3% time spent grazing. Grazing activity patterns were generally similar for pronghorn and cattle with alternating periods of grazing and resting but ‘…. the pronghorn engages in frequent, relatively short alternating bouts of foraging and resting activity, … Cattle apparently engage in longer alternating bouts of feeding and resting, which yield more extreme hourly values of percent time in each activity … both species demonstrate a behaviour pattern of alternating periods of grazing and resting, but for cattle both the amplitude and the period of this cycle is greater than for pronghorn’. (Ellis & Travis 1975, pp. 416- 417.)

Pronghorn grazing patterns changed seasonally. Time spent grazing averaged 54% of the daylight period between March and October, increased to 70% in November- December and decreased to 35% in January-February. Grazing frequency (no. of feeding bouts/day) decreased from 5 to 3 over the same period while grazing intensity (% time This content downloaded from on Sun, 21 Feb 2021 19:35:21 UTC All use subject to 350 Feeding ecology and niche separation spent feeding per bout) increased (Schwartz, Mathews & Nagy 1976a). Comparable seasonal changes in feeding patterns have been quantified for free-ranging elk (Cervus elaphus canadensis) by Gates (1980). Pronghorns spent most of their feeding time (68%) grazing slopes and ridge tops in May and June, but by October 65% of their grazing time was in lowland drainages. Cattle consistently favoured lowland drainages and moist slopes from May through October (Schwartz, Mathews & Nagy 1976a). DISCUSSION The references cited in the Introduction point out how and why many aspects of ungulate diet selection, foraging behaviour, feeding ecology and community structure can be rel

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