Host plant direct defence against eggs of its specialist herbivore,Heliothis subflexa

1. The insect Heliothis subflexa Guenée is a specialist on plants in the genus Physalis. In the present study, the physical response of Physalis leaves to egg deposition by H. subflexa is described. 2. It was observed that the leaves of Physalis plants respond to the eggs of H. subflexa, while co‐occurring non‐host plants do not. Leaves of Physalis angulata L. and Physalis pubescens L. respond to H. subflexa eggs by the formation of (i) necrotic tissue, (ii) undifferentiated cells that form a bump (neoplasm) under the eggs of this herbivore, or (iii) both types of responses. 3. Greenhouse experiments showed that 64% of eggs laid on P. angulata elicited a response, and that a response to an egg decreased the probability of hatching. Further experiments in the field with P. angulata showed that the mean response to eggs by leaves was 31%, and that this response increased as temperature increased. Field experiments also confirmed that a plant response to an egg decreased the probability of hatching and increased the probability of removal from the plant by physical dislodgement or predation. 4. Eggs that elicited a response had a 25% lower probability of hatching and a 28% lower probability of remaining on the plant, resulting in an average fitness cost of 19.3% for H. subflexa. This is the first study to show an induced direct physical defence of a plant against eggs of a noctuid moth.     

Response of Elk to Changes in Plant Production and Nutrition Following Prescribed Burning

Abstract: Researchers have ascribed use of areas by grazers after burning to changes in plant community structure, community composition, nutritional quality, and seasonal availability. Researchers can better evaluate these alternatives if they monitor changes in plant communities following burning concurrently with changes in animal use. We examined responses of elk (Cervus elaphus) to prescribed burning of areas dominated by sagebrush (Artemisia spp.) in south-central Montana, USA, within which we monitored changes in plant production, nutritional quality, and community composition and diversity from 1989 to 1999. Elk increased use of burned sites 1–2 years after burning, then reduced use to levels associated with preburn conditions over the next 3–10 years. Burning transformed low-diversity, sagebrush-dominated communities into relatively high-diversity, grass- and forb-dominated communities that persisted for 10 years, but forage biomass and protein content declined on burned sites after initial short-term increases. Changes in elk use closely tracked changes in production and nutritional quality of plants. Therefore, we concluded that increases in quantity and quality of forage were the primary cause for increased use of burned sites by elk. Managers may observe only short-term responses from elk following burning but can expect longer-term increases in plant diversity and persistence of grass—forb communities on burned sites for >10 years that may be important to elk or other grazing ungulates.     

Population Irruptions of Northern Bobwhite: Testing an Age-Specific Reproduction Hypothesis

Abstract: Age-specific reproduction has been suggested for northern bobwhite (Colinus virginianus) and has been hypothesized as a factor contributing to population irruptions. However, little research has been conducted on the subject. We conducted a laboratory and field study to determine if age-specific reproduction occurred in northern bobwhites. Our objectives were to compare 7 reproductive measures (% F nesting, date of first incubated nest, egg-laying rate, nesting rate, clutch size, egg mass, and egg hatchability) between first- and second-year breeders and determine if differential reproduction was impacted by diet quality. The laboratory study consisted of a 2 × 2 factorial experiment with age and diet quality (low protein [12%] and high protein [24%]) as the factors. Data for the field study represented a 6-year data set of bobwhite reproduction (May-Sep 2000-2005) obtained from an ongoing radiotelemetry study in southern Texas, USA. We documented similar productivity (i.e., % F laying, egg-laying rate, and egg mass) and timing of laying (i.e., date of first egg) between juvenile (n = 33) and adult bobwhites (n = 27) in our laboratory study. However, females on the high-protein diet exhibited a greater egg-laying rate than females on the low-protein diet. Under field conditions, we also documented no difference in productivity (% F nesting, nesting rate, clutch size, egg hatchability) and timing of nesting (date of first incubated nest) between age classes (n = 59 juv and 32 ad). Our findings do not support early suppositions of age-specific reproduction in quail. Quail irruptions should not be influenced by population age structure as it relates to age-specific reproduction.     

An Experimental Method for Studying the Differentiation of Vessel Endings

A simple experimental method for studying the differentiationof vessel endings is described. Vessel endings are induced andtheir location is determined experimentally along an internodeby a complete horizontal cut. The frequency of vessel endingsis very high in the first 5 mm immediately below the cut andtheir number declined sharply in the basipetal direction. Patternsof the secondary wall of complete and partly dissolved vesselendings are demonstrated. Hydraulic safety zone, Luffa cylindrica, vessel differentiation, vessel endings, xylem anatomy     

Management Implications of Cover Selection Data: Northern Bobwhite Example

Abstract: We derived a method of estimating the direction and magnitude of cover changes for potentially maximizing wildlife abundance on an area. We illustrate the method with data on cover selection by northern bobwhites (Colinus virginianus) collected in the Texas Panhandle from 2000 to 2003. We used radiotelemetry to determine use of cover associations, Geographic Information System analysis to determine their availability, and logic related to use-availability analysis to collapse 95% kernel home ranges to usable space. Bobwhites selected mixed-shrub cover consisting of sand plum (Prunus angustifolia) and fragrant sumac (Rhus aromatica), and they avoided or neutrally used 8 other cover associations. However, grass upland and sand sagebrush (Artemisia filifolia) associations occurred in ≥86% of home ranges (n = 96 bobwhites with ≥30 radiolocations). Usable space averaged 54.2% ± 1.72 SE of kernel home ranges. The data indicated that adding about 226 ha of mixed-shrub cover or a structural homologue while simultaneously reducing the quantity of most other cover associations would maximize bobwhite abundance. An area with 30–60% mixed-shrub cover, with the balance in grass upland and sand sagebrush, and with cover dispersed such that no point was >30 m from mixed-shrub cover was hypothetically optimal for bobwhites in our region. Within certain constraints (e.g., financial, social, edaphic), managers can apply this method by manipulating cover types through relevant management practices (e.g., planting, prescribed burning, mechanical removal of vegetation). This method, with minor modification, could also be used to decrease usable space on an area, and thus decrease wildlife densities, should that be the manager's objective.