D. M. Swift

Stability of African pastoral ecosystems: alternate paradigms and implications for development

JIM ELLIS took undergraduate work in animal husbandry at the University of Missouri and also obtained his Master of Science degree there studying wildlife biology. In 1970, he received his Ph.D. in Zoology at the University of California at Davis, where he was a National Institute of Health trainee in systems ecology. Shortly thereafter, he held a National Science Foundation postdoctoral fellowship at the University of Bristol working on systems analysis of mammalian social systems. He joined the Natural Resource Ecology Laboratory of Colorado State University as a Research Ecologist in 1971. He is currently the Associate Director of the Laboratory. Jim has enjoyed immense success in developing research programs; during the last decade he directed or played a major role in 12 successful proposals, collectively exceeding three milliondollaninsuppott. He has publishedextensively, withmost of his work focussing on processes regulatinggrazing systems. Jim has served as a consultant to the U.S. Senate, as well as the govcmmcnt of Saudi Arabia and the Norwegian Agency for International Development. His must recent project uses a systems approach to understand the controls on stability and persistence of a pastoral ecosystem in East Africa.

Relative growth rates and the grazing optimization hypothesis

SummaryA mathematical analysis of the changes in plant relative growth rates necessary to increase aboveground production following grazing was conducted. The equation derived gives an isoline where production of a grazed and ungrazed plant will be the same. The equation has four variables (mean shoot relative growth rate, change in relative growth rate after grazing, grazing intensity, and recovery time) and may be analyzed graphically in a number of ways.Under certain conditions, small increases in shoot relative growth rate following grazing will lead to increased aboveground production. Under other conditions, very large increases in relative growth rate after grazing can occur without production being increased over that of ungrazed plants. Plants growing at nearly their maximum potential relative growth rate have little opportunity to respond positively to grazing and potentially can sustain less grazing than plants with growth rates far below maximum. Plants with high relative growth rates at the time of grazing require large increases in growth rate while slow growing plants require only small increases. High grazing intensities are least likely to increase production and high grazing frequencies require greater responses than infrequent grazing events.

Energy Extraction and Use in a Nomadic Pastoral Ecosystem

An analysis of annual energy flows in an arid tropical ecosystem inhabited by nomadic pastoralists provides insight into a subsistence life-style that has persisted in droughted environments for hundreds to thousands of years. Although a large fraction of the total energy consumed by the Ngisonyoka of Kenya followed a single pathway from plant to animal to human, they also harvested solar energy from a relatively diverse assemblage of energy flow channels. Energy utilization and conversion efficiencies were generally low, as the system is maintenance-rather than production-oriented. Energy flow to maintenance must be relatively high to support biotic responses that enable tolerance of abiotic variability and to stabilize energy flow under the stress of severe droughts. Energy utilization by the Ngisonyoka is therefore consistent with ecological patterns that promote rather than diminish ecological stability under stress.

Bias and Random Errors in Estimators of Net Root Production: A Simulation Approach

Simulation of net primary production in a grassland and subsequent calculations of belowground net production revealed substantial sources of error that may be common to all estimates of belowground net production from field data. Inherent bias in the most frequently used estimators and a large counterintuitive effect of sample variability require that techniques be carefully considered before conclusions are drawn based upon estimates of belowground net production.

Structure and Productivity of Grassland Small Mammal Communities Related to Grazing-Induced Changes in Vegetative Cover

Effect of grazing on the structure and productivity of small mammal communities in four types of North American grasslands is examined quantitatively using data collected during a 4-year period. Small mammal communities in tallgrass and montane grasslands appear more affected by grazing and the subsequent reduction in vegetative cover (=total above-ground standing crop of plants) than do small mammal communities in shortgrass and bunchgrass grasslands. This trend is evident when small mammals in grazed versus ungrazed habitats are compared with regard to mean community biomass, annual community respiration, production, and consumption, mean species diversity and evenness, proportional species and functional group composition, seasonal dynamics of community biomass, and temporal variation in proportional species composition. These results lend further support to the hypothesis that the general composition of grassland small mammal communities is determined primarily by structural attributes of the habitat.

Differential Loss of Fat and Protein by Mule Deer during Winter

Body composition of hand-reared mule deer (Odocoileus hemionus) was studied by use of tritiated water (HTO) over a 120-day period. Energy intake was controlled at different levels for three treatment groups. All treatment groups received submaintenance rations to ensure catabolism of energy reserves. Changes in total body water indicated catabolism of both fat and protein reserves. High-intake animals lost less fat (38%) than either medium(46%) or low(67%) intake deer. High and medium groups lost similar amounts of protein (16% and 18%, respectively), whereas low-intake animals lost 31% of their body protein. Significant loss of protein occurred in all groups within the first 40 days. Fat reserves were depleted at similar rates among treatments. Rates of protein loss between high-and medium-intake groups were similar, but the low-intake group differed significantly. Analysis of the amount of energy contributed to the energy pool by catabolism of fat or protein suggested three phases of protein catabolism, similar to those observed in starvation studies with other mammals. Consequences of fat and protein catabolism in wintering mule deer are discussed. J. WILDL. MANAGE. 49(1):80-85 During winter, wild North American ruminants may face a shortage of forage (Moen 1976, Wallmo et al. 1977). Even if an adequate quantity of forage is available, its quality may be so low that it cannot be effectively utilized (Short et al. 1966, Dietz 1967); because low quality forages are not readily digestible, they may not support large rumen microflora populations. As a result, wintering animals may extract energy so slowly that they enter negative energy balance despite presence of adequate quantities of available forage. Additionally, the rate at which ungulates are able to extract protein from such forages may be insufficient to meet their metabolic requirements. Thus, even when the quantity of winter forage is not limiting, forage quality may still impede the rate of energy acquisition by wild ungulates. During periods of prolonged negative energy balance, an animal draws upon fat and protein to meet its energy requirements. Differential use of these two reserves may affect the animals survival probability or production of viable offspring. Catabolism of fat for maintenance appears to be a normal, nondetrimental part of the animals annual cycle. Both synthesis and catabolism of fat proceed at high levels of energetic efficiency (van Es 1977). Protein synthesis and catabolism for energy use is less efficient than that of adipose tissue (Thorbek 1977); therefore, it is not energetically advantageous to rely heavily upon protein reserves to meet an energy deficit. Cahill (1970) suggested that mammals could not withstand a loss of onethird of total protein stores. Little is known about differential use of these two energy reserves in wild ruminants. de Calesta et al. (1975) suggested that protein and fat catabolism occurred simultaneously in starving mule deer. Panaretto (1964) showed both fat and protein catabolism had occurred in two groups of undernourished domestic sheep. Conditions that trigger substantial protein catabolism are not known, nor is it understood how the magnitude or duration of nutritional deprivation affects priorities associated with use of adipose and lean body tissue. Accordingly, we investigated in vivo catabolism of protein and fat reserves of mule deer during winter. Financial support was provided by Fed. Aid Proj. W-126-R, Colo., and Natl. Sci. Found. grant #DEB 7917293. We wish to thank P. H. Neil, D. L. Baker, E. S. Williams, P. A. Smith, and K. N. Callahan for their assistance in all phases of this investigation. MATERIALS AND METHODS

Estimating aboveground net primary production in grasslands: A simulation approach

Abstract A simulation model which reflected the seasonal dynamics of biomass in a North America mixed prairie was employed to evaluate methods of calculating aboveground net primary production from harvest data. The methods of calculating aboveground net primary production were evaluated under conditions with and without variability in the data. A multivariate normal random number generator was utilized in the variance case. In the no variance case, methods which utilized only live biomass underestimated aboveground net primary production by approximately 42%. Methods which utilized live and recent dead (senesced) biomass produced estimates very close to the model value. Variance in the data resulted in overestimation of aboveground net primary production with the degree of overestimation related to the sampling frequency. Use of a simple simulation model which simultaneously makes use of all the data to arrive at an estimate of aboveground net primary production may prove to be superior to the statistical estimators.

Immediate Effects Of Prescribed Burning On Mineral Soil Nitrogen In Ponderosa Pine Of New Mexico

Three 0.1-ha ponderosa pine (Pinus ponderosa Dougl. ex Laws) sites were burned in the fall of 1981. The burn was mainly a ground fire. Burn intensity was 980, 1760, and 2280 kJ s−1 m−1 on sites 1, 2, and 3, respectively. We analyzed the mineral soils on each of these sites for total N, NO2−+NO3−-N and NH4+-N prior to prescribed burning, 1 d postburn, and 30 d postburn. On the most intense burn, NH4+-N levels increased threefold from preburn (10 ppm) to 1 d postburn (32 ppm), but declined somewhat 30 d following the burn (24 ppm). Concentrations of NO2+NO3−-N on site 3 rose from 1 ppm preburn and 1 d postburn to 5 ppm 30 d postburn. There were no significant differences in soil total N after burning. Immediate postburn inorganic N values for ponderosa pine mineral soils have not been previously reported in the literature. It is important to investigate burned soils immediately after burning to better understand sequential processes involved in postfire inorganic N dynamics.

Association of relative food availabilities and locations by cattle.

Four yearUng steers were trained and observed in a parallel-arm maze. Tbe purpose was to determine if cattle bad tbc ability to associate locations witb relative food availabilities. Tbc study consisted of 3 phases. In phase 1, ail 5 arms contabred 0.4 kg of gabt. In phase 2, the amount of grahr hr each arm was systematicilly varied from 0.1 to 0.8 kg. In phase 3, placement of grain was reversed. Steers performed efficiently in all 3 phases of tbe study. The overaIl-mean number of correct cboicee in tbe first 5 entrancea was 4.69 as compared to 3.73 by chance. Arms selected for choices 2,3, and 4 during tbe Iast 5 MaIs of pbase 2 were dIffercut (p<O.O5) from those selected during tbe last 5 trials of pbase 3. For tbe last 5 triah of phases of 2 and 3, arms selected in choices 1,2, and 3 contained 0.4,0.6 and 0.8 kg of grabr on 85% of tbe MaIs. Steers appeared to order their choices from larger to smaller rewards. Steers apparently can remember not only where they have foraged, but aIso tbe amount of food found there.

Response of a Small Mammal Community to Water and Nitrogen Treatments in a Shortgrass Prairie Ecosystem

The response of small mammal communities to continuous water and nitrogen treatments on 1 hectare (ha) plots of shortgrass prairie was monitored over a 4 year period. Small mammals were live-trapped 18 times on each of eight plots representing water, nitrogen, water plus nitrogen, and control treatments. Four species ( Microtus ochrogaster , Onychomys leucogaster, Peromyscus maniculatus , and Spermophilus tridecemlineatus ) were captured. Analysis of variance with the variability in population densities (individuals/ha) partitioned between treatments and sample dates indicates significant treatment effects for all four species. Population densities of Microtus and Peromyscus were significantly higher (P < .001 and F < .02, respectively) on the water plus nitrogen treatment than on other treatments; Onychomys populations were significantly higher ( P < .05) on the nitrogen and control treatments than on the water and water plus nitrogen treatments; Spermophilus populations were significantly higher ( P < .05) on the nitrogen and control treatments than on the water plus nitrogen treatment. Analysis of variability in total small mammal biomass (grams, g, live weight/ha) also indicates significant treatment effects. Total biomass on the water plus nitrogen treatment was significantly higher ( P < .001) than on other treatments. Proportional species composition of the small mammal communities differed, with Microtus occurring primarily on the two “wet” treatments, Onychomys occurring primarily on the two “dry” treatments, and Peromyscus and Spermophilus occurring on all treatments. The ratio of community respiration to community consumption on the water plus nitrogen treatment, and to a lesser extent on the water treatment, is lower than on the nitrogen and control treatments as a result of the higher proportion of grazing herbivores (that is, Microtus ) on these treatments. Small mammal utilization of food resources never exceeded 4 percent of the available plants or 34 percent of the available arthropods on any of the treatments. Results tentatively support the hypothesis that changes in the small mammal communities were tightly coupled to changes in vegetation structure.