Montague W. Demment

The importance of scale of patchiness for selectivity in grazing herbivores

Abstractu2002The notion that spatial scale is an important determinant of foraging selectivity and habitat utilization has only recently been recognized. We predicted and tested the effects of scale of patchiness on movements and selectivity of a large grazer in a controlled field experiment. We created random mosaics of short/high-quality and tall/low-quality grass patches in equal proportion at grid sizes of 2×2 m and 5×5 m. Subsequently, we monitored the foraging behaviour of four steers in 16 20×40 m plots over 30-min periods. As predicted on the basis of nutrient intake maximization, the animals selected the short patches, both by walking in a non-random manner and by additional selectivity for feeding stations. The tortuosity of foraging paths was similar at both scales of patchiness but selectivity was more pronounced in large patches than in small ones. In contrast, the number of bites per feeding station was not affected by patch size, suggesting that selection between and within feeding stations are essentially different processes. Mean residence time at individual feeding stations could not be successfully predicted on the basis of the marginal-value theorem: the animals stayed longer than expected, especially in the less profitable patch type. The distribution of the number of bites per feeding station suggests a constant probability to stay to feed or to move on to the next feeding station. This implies that the animals do not treat larger patches as discrete feeding stations but rather as a continuous resource. Our results have important implications for the application of optimal foraging theory in patchy environments. We conclude that selectivity in grazers is facilitated by large-scale heterogeneity, particularly by enhancing discrimination between feeding stations and larger selection units.

Mechanisms of handling time and intake rate of a large mammalian grazer

Abstract The effects of sward structure and bite weight ( W ) on bite rate in cattle ( Bos taurus ) were examined to explain the behavioural components of handling time. Three oesophageally fistulated steers grazed homogeneous, hand-constructed swards of Paspalum dilatatum Poir. or Medicago sativa L., in a sward area of approximately 0.36 m 2 , for 60–212 s. Three types of jaw movements (JM) were distinguished: manipulative JM that gather herbage into the mouth, chewing JM, and compound JM that manipulate fresh herbage and chew herbage already in the mouth within one cycle of opening and closing of the jaws. Intake rate ( I , g min −1 ) was a discontinuous asymptotic function of W: I = W max (0.0337,0.0201 + 0.0095 ∗ W) . Sward height and bulk density did not significantly affect I beyond the effects of W . Time per bite was 2.0 s when W ≈ 1.29 g, and increased linearly with W when W >1.29 g. Linear regression of time per bite on total number of JM explained 96% of the variance. A non-linear relation between total JM per bite and W comprised a linear relation between total chews per bite and W , and a constant number of total manipulative JM per bite. When W increased up to c . 1.5 g, chewing requirements were met by compound JM. Above W of 1.5 g, the overlap of chewing and manipulation reached a maximum, so total JM increased with W . The importance of compound JM and the potential for overlap between chewing and searching are discussed in the context of foraging models.

Kenyan School Children Have Multiple Micronutrient Deficiencies, but Increased Plasma Vitamin B-12 Is the Only Detectable Micronutrient Response to Meat or Milk Supplementation

Animal source foods (ASF) can provide micronutrients in greater amounts and more bioavailable forms compared to plant source foods, but their intake is low in many poor populations. However, the impact of ASF on micronutrient status of undernourished populations has not been assessed. Supplemental meat (60-85 g/d), milk (200-250 mL/d) or energy (isocaloric with the meat and milk, 240-300 kcal/d) were randomly assigned to 555 undernourished school children aged 5-14 y in a rural malaria-endemic area of Kenya, at one school meal daily for one school year. Blood and stool samples were collected at baseline and after 1 y to assess stool parasites, malaria, hemoglobin, serum or plasma C-reactive protein, ferritin, iron, zinc, copper, vitamin B-12, folate and retinol, and erythrocyte riboflavin. At baseline, there was a high prevalence of micronutrient deficiencies (iron, zinc, vitamins A and B-12 and riboflavin), yet plasma ferritin was low in few children, and none had low serum copper. At the end of the year of supplementation, plasma vitamin B-12 concentrations were significantly increased in children fed the Meat or Milk meal; prevalence of severe plus moderate deficiency fell from 80.7% at baseline to 64.1% in the Meat group and from 71.6 to 45.1% in the Milk group, respectively. No significant improvement was observed in the status of other micronutrients compared to the Energy and Control groups, although malaria and other infections may have obscured effects. Supplementation with small amounts of meat or milk reduced the high prevalence of vitamin B-12 deficiency in these children.

Patch selection by cattle: maximization of intake rate in horizontally heterogeneous pastures☆

Abstract The role of various perceptual cues on selectivity patterns of cattle grazing heterogeneous swards were studied in a controlled experiment. Patches of different height and/or bulk density, representing similar or dissimilar potential instantaneous intake rate (IR), were created in a ryegrass ( Lolium perenne L.) pasture to study foraging responses of cattle ( Bos taurus ) to heterogeneity in patch structure. The experiment involved three heterogeneity treatments with two patch types each. One patch type (short-dense) was present in all three treatments. In all treatments, cattle encountered and entered both patch types available with the same frequency. In contrast, average residence time and total number of bites removed were greater in the patch type that allowed greater instantaneous intake rate. Patch utilization and residence time agreed with qualitative predictions of a rate-maximizing model. Residence time in short-dense patches was shortest in the treatment that allowed the greatest intake rate, and longest in the one that allowed the lowest intake rate. Short-dense patches were relatively avoided when the alternative patch was tall and dense, but they were preferred when the alternative patch was short and sparse. The pattern of relative preference for the different patches ruled out vegetation height, density and herbage mass as cues for the allocation of residence time. Steers consistently spent more time in the patches that allowed greater bite weights and instantaneous intake rate while at the patch. Relative preference of patches exhibited a pattern of overmatching, under the assumption that herbage intake was the reward to grazing behavior. Overmatching indicates that behavior was allocated to patches more than proportionally to the relative rewards. However, the degree of overmatching was less than predicted by maximization of intake rate. Grazing behavior and residence time did not respond to repeated short-term exposures to a treatment within the same day.

Validation of the Household Food Insecurity Access Scale in rural Tanzania.

OBJECTIVEnThe purpose of the present study was to test the construct validity, internal consistency and convergent validity of the Household Food Insecurity Access Scale (HFIAS) in measuring household food insecurity in rural Tanzania, and to determine socio-economic characteristics associated with household food insecurity.nnnDESIGNnKey informant interviews and a cross-sectional survey were conducted in February and March 2008.nnnSETTINGnRural Iringa, Tanzania.nnnSUBJECTSnKey informant interviews were conducted with twenty-one purposively selected male and female village leaders. For the household surveys, a sample of 237 households with mothers (caregivers) and at least one child between 1 and 5 years of age were included.nnnRESULTSnApproximately 20.7 % of the households were categorized as food-secure, 8.4 % as mildly food-insecure, 22.8 % as moderately food-secure and 48.1 % as severely food-insecure. Two main factors emerged from the rotated principal component factor analysis: (i) insufficient food quality; and (ii) insufficient food intake. Both factors explained 69 % of the total variance. The full food insecurity scale and the two subscales had good internal consistency (Cronbachs alpha = 0.83-0.90). Food security, as measured by HFIAS, was positively associated with maternal education, husbands education, household wealth status, being of an agricultural rather than pastoral tribe and animal-source food consumption; it was negatively associated with maternal age and household size.nnnCONCLUSIONSnThe HFIAS measurement instrument shows validity and reliability in measuring household food insecurity among poor households in rural Tanzania.

Allometric scaling predicts preferences for burned patches in a guild of East African grazers.

The high herbivore diversity in savanna systems has been attributed to the inherent spatial and temporal heterogeneity related to the quantity and quality of food resources. Allometric scaling predicts that smaller-bodied grazers rely on higher quality forage than larger-bodied grazers. We replicated burns at varying scales in an East African savanna and measured visitation by an entire guild of larger grazers ranging in size from hare to elephant. We found a strong negative relationship between burn preference and body mass with foregut fermenters preferring burns to a greater degree than hindgut fermenters. Burns with higher quality forage were preferred more than burns with lower quality forage by small-bodied grazers, while the opposite was true for large-bodied grazers. Our results represent some of the first experimental evidence demonstrating the importance of body size in predicting how large herbivores respond to fire-induced changes in plant quality and quantity.

Sex differences in giraffe foraging behavior at two spatial scales

Abstract We test predictions about differences in the foraging behaviors of male and female giraffes (Giraffa camelopardalis tippelskirchi Matchie) that derive from a hypothesis linking sexual size dimorphism to foraging behavior. This body-size hypothesis predicts that males will exhibit specific behaviors that increase their dry-matter intake rate relative to females. Foraging behavior was examined at two hierarchical levels corresponding to two spatial and temporal scales, within patches and within habitats. Patches are defined as individual trees or shrubs and habitats are defined as collections of patches within plant communities. Males were predicted to increase dry-matter intake rate within patches by taking larger bites, cropping bites more quickly, chewing less, and chewing faster. Within habitats, males were expected to increase intake rate by increasing the proportion of foraging time devoted to food ingestion as opposed to inter-patch travel time and vigilance. The predictions were tested in a free-ranging population of giraffes in Mikumi National Park, Tanzania. Males spent less total time foraging than females but allocated a greater proportion of their foraging time to forage ingestion as opposed to travel between patches. There was no sex difference in rumination time but males spent more time in activities other than foraging and rumination, such as walking. Within patches, males took larger bites than females, but females cropped bites more quickly and chewed faster. Males had longer per-bite handling times than females but had shorter handling times per gram of intake. Within habitats, males had longer average patch residence times but there was no significant sex difference in inter-patch travel times. There was no overall difference between sexes in vigilance while foraging, although there were significant sex by habitat and sex by season interactions. Although not all the predictions were confirmed, overall the results agree qualitatively with the body-size hypothesis. Sex-related differences in foraging behavior led to greater estimated intake rates for males at the within-patch and within-habitat scales.

Providing Micronutrients through Food-Based Solutions: A Key to Human and National Development

To alleviate poverty in developing countries, economies must grow. Without the necessary investments in human capital, national economic growth may not lead to poverty alleviation and socioeconomic development, nor be sustainable. Economic growth that leads to poverty alleviation is fueled by the creative and physical capacities of people. The impact of micronutrient malnutrition is established early in life, leading to growth stunting, lower cognitive abilities, lethargy and poor attention, and greater severity and rates of infection. These effects limit educational progress, physical work capacity and life expectancy, thereby reducing individual lifetime productivity and the aggregate ability of the population to enhance its well-being and participate in national and global markets. The diets of the poor are largely cereal-based, monotonous and lacking in diversity and micronutrients. Animal source foods (ASF) have been an important factor in human evolution, a component of what was an historically diverse diet and an important source of micronutrients. Poverty and micronutrient malnutrition positively influence each other. This poverty micronutrient malnutrition (PMM) trap requires outside inputs to change the state of development in developing countries. Nutrition interventions have been excellent investments in development. More productive interaction between agricultural scientists and nutritionists, supported by a strong federal agenda for development, is needed to break the PMM trap. In the end, food is the means by which nutrients are delivered. Food-based approaches will require long-term commitments, but are more likely to be sustainable because they are part of a development process that leads to long-term economic growth.

Nutritional ecology of dimorphic herbivores : digestion and passage rates in Nubian ibex

We compared forage digestion and passage rates among three groups of Nubian ibex (Capra ibex nubiana) — mature males, non-lactating females, and lactating females — to test hypotheses relating intraspecific digestive ability to body mass and reproduction costs. We hypothesized that large males (60 kg) would exhibit longer forage retention times and more complete digestion of fermentable cell walls than adult females (23 kg). We tested these predictions by measuring digestion and retention of a grass hay and an alfalfa hay, forages that exhibited contrasting rates and extents of cell wall digestion. Consistent with predictions, males retained both forages longer than non-lactating females. However, by substantially increasing gut fill, lactating females increased both intake and retention time with respect to non-lactating females. Contrary to predictions, all three groups digested the grass (66% digestible) and alfalfa hay (63%) equally well. Alfalfa cell wall was less digestible than that of grass hay (60% vs 69% digestible), and retention time of alfalfa was consistently, but not statistically significantly, shorter. Fiber digestion was not correlated with retention time, emphasizing the ability of behavioral processes to modify digestion rate. We postulate that females achieved their greater digestion rate by masticating forages much more thoroughly than males.

Successional patterns of mortality and growth of large trees in a Panamanian lowland forest

All trees ≥ 19.1 cm d.b.h. (diameter at breast height) in three 1-ha forest plots in Panama were tagged and measured in 1975 and recensused in 1980 and 1988 to examine mortality, growth and recruitment. Plots ranged in age from old second-growth (plot 1), to disturbed primary forest of intermediate age (plot 2) to undisturbed primary forest perhaps 500 years old (plot 3). Common species were classified into two regeneration classes - gap-positive recruitment (GPR) or gap-neutral recruitment (GNR) - on the basis of other studies. As plot age increased, tree density decreased slightly and forest composition changed from dominance of GPR to GNR trees. Species diversity was similar in plots 1 and 3 and lower in plot 2. Basal area per stem and total basal area increased with plot age (...)