Microclimates of the arid lands ecology reserve, 1968--1975

Thorp, John M.; Hinds, W.T.

doi:10.2172/7087102

Cited by 24 publications

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“…The present study was confined to a 40-km 2 area (20 x 2 km) averaging =370m in elevation. Average rainfall for ALE at this elevation is 25 cm/yr; average daily maximum and minimum temperatures range from l4°C and -l6°C in January to 44°C and woe in July (Thorp and Hinds 1977). The short-term (1 mol yr) unpredictability of precipitation here has been demonstrated by Wiens (1974) using patterns of serial autocorrelation of monthly rainfall.…”

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confidence: 68%

Dietary Relationships among Shrubsteppe Passerine Birds: Competition or Opportunism in a Variable Environment

Rotenberry¹

1980

Ecological Monographs

118

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The suggestion that in less stable environments resource limitation and subsequent interspecific competition may be relatively unimportant in determining bird community structure is explored by examining the dietary relationships within a guild of three ground—foraging passerine birds (Horned Lark, Sage Sparrow, and Western Meadowlark) in the shrubsteppe of southeastern Washington, USA, an area of severe, arid, unstable climate. General dietary analyses indicated a strong temporal component to the organization of bird diets: different species collected at the same time ate much the same things while the same species collected at different times ate different things. This pattern is reinforced by cluster analysis and stepwise discriminant analysis. Similarities in diet extended to other components as well. Dietary diversities tended to be the same for contemporaneous collections of birds, as did average prey sizes, although the latter evidenced a few statistically significant exceptions. Theoretically predicted relationships between diet and trophic structure morphology emerged only at the most general level, and even then were not always observed. In general, differences in body size or bill length were insufficient to account for variations in prey sizes, although meadowlarks did on occasion take significantly larger items than the other, smaller species. Average prey size was significantly correlated with the proportion of seeds in the diet and varied seasonally as seed consumption varied. Several aspects of this study indicate that shrubsteppe passerines are largely opportunistic in their foraging and diet selection, and that the apparent absence of fine tuning to their competitive milieu is most likely a function of the variable environment in which they coexist.

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confidence: 68%

Dietary Relationships among Shrubsteppe Passerine Birds: Competition or Opportunism in a Variable Environment

Rotenberry¹

1980

Ecological Monographs

118

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“…The study plot was located 6 km east of the Cabin Lake Guard Station, Deschutes National Forest, Oregon (43°30' N, 121°00' W), at an elevation of 1390 m. Precipitation averages 28.8 em per year, most (70%) occurring during the October-April "bioyear" (Thorp and Hinds 1977). The study plot was located 6 km east of the Cabin Lake Guard Station, Deschutes National Forest, Oregon (43°30' N, 121°00' W), at an elevation of 1390 m. Precipitation averages 28.8 em per year, most (70%) occurring during the October-April "bioyear" (Thorp and Hinds 1977).…”

Section: Study Area and Speciesmentioning

confidence: 99%

A Lesson in the Limitations of Field Experiments: Shrubsteppe Birds and Habitat Alteration

Wiens¹,

Rotenberry²,

Horne³

1986

Ecology

128

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We manipulated the habitat composition and structure within territories of birds breeding in the Artemisia-dominated shrubsteppe of central Oregon in order to assess how closely individuals track habitat in features such as territory placement or size or behavioral budgeting and space use. We removed 75, 50, 25, and 0% of the shrub individuals from 625-m 2 blocks in a checkerboard design. Over the following 7 yr we monitored territorial locations and sizes and breeding densities of Homed Larks (Eremophila alpestris), Sage Sparrows (Amphispiza belli), and Brewer's Sparrows (Spizel/a breweri) on the manipulated area and an adjacent unaltered control area. Activity and substrateuse patterns and intensity of use of the different treatment blocks within the manipulated area were also determined for the two sparrow species. Sage Sparrows, which from our previous studies appear to be more closely linked to shrub (sagebrush) coverage than the other species, did not respond to the manipulation at a local population level. The manipulation apparently did affect territory placement and densities of Brewer's Sparrows and Homed Larks in 1980-1982, but these trends were not consistent over the entire postmanipulation period. Densities of all species varied among years. For Brewer's Sparrows and Homed Larks these variations did not parallel those in nearby census locations, but Sage Sparrow densities varied in the same ways over all the locations. These variations appeared to parallel variations in bioyear (October-April) precipitation, with a 1-yr time lag. Individuals of both sparrow species altered the details of their activity budgeting, but not their substrate-use patterns, in response to the manipulation. Both species clearly expressed an affinity for unmanipulated blocks within the manipulation area.This experimental manipulation is complicated by influences of time lags on individual and population responses that may stem in part from site tenacity by breeding adults, leading them to return to previous breeding locations in years following the manipulation despite the habitat changes. Further, the spatial scale on which the manipulation was conducted may have been inappropriate to gauge responses at the population level. We suggest that these complications may plague many field experiments in ecology.

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“…To characterize precipitation in a manner relevant to biological production in this ecosystem, we summed precipitation amounts for October-April preceding each breeding season (''bioyear'' precipitation;Daubenmire 1970, Thorp andHinds 1977). Weather Bureau weather station (''Fremont'') located ϳ2 km from the study plot in comparable habitat and topography.…”

Section: Study Areamentioning

confidence: 99%

Foraging Patch Selection by Shrubsteppe Sparrows

Rotenberry

Wiens

1998

Ecology

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We used bird-centered vegetation measurements to assess selection of shrubdefined patches by foraging Sage Sparrows (Amphispiza belli) and Brewer's Sparrows (Spizella breweri) over a period of 3 yr. Principal components of habitat variation based on a random sample of 900 patches were patch size, species composition (big sagebrush [Artemisia tridentata] vs. green rabbitbrush [Chrysothamnus viscidiflora] vs. gray rabbitbrush [C. nauseosus]), and plant vigor. Both bird species differed from random (P Ͻ 0.001) in their selection of patches in each year, but did not differ from each other. Patch structure varied significantly among years (P Ͻ 0.001), as did each species' use of patches. Betweenyear changes in the two bird species' selection patterns were highly correlated with changes in the habitat, and with each other. These correlations suggest that shrubsteppe sparrows ''track'' interannual variation in patch composition and structure (which is presumably induced by precipitation variation) but maintain nonrandom use patterns within years.

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Microclimates of the arid lands ecology reserve, 1968--1975

Cited by 24 publications

References 0 publications

Dietary Relationships among Shrubsteppe Passerine Birds: Competition or Opportunism in a Variable Environment

Dietary Relationships among Shrubsteppe Passerine Birds: Competition or Opportunism in a Variable Environment

A Lesson in the Limitations of Field Experiments: Shrubsteppe Birds and Habitat Alteration

Foraging Patch Selection by Shrubsteppe Sparrows

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