Ecological monophagy in Tasmanian Graphium macleayanum moggana with evolutionary reflections of ancient angiosperm hosts

Local host plant specialization in an insect herbivore may be caused by numerous factors, including host-specific natural enemy pressures or a local lack of suitable host-plant choices that are available elsewhere in its range. Such local specialization or ＂ecological monophagy＇, for whatever reason, may reflect reduced ability to behaviourally accept or physiologically utilize other allopatric hosts that are naturally used elsewhere by the species. We tested this feeding specialization hypothesis using the Tasmanian subspecies of Macleay＇s swallowtail butterfly, Graphium macleayanum moggana （Papilionidae）, which uses only a single host-plant species, Antherosperma moschatum （southern sassafras, of the Monlmiaceae）. Further north, this same butterfly species （G. m. macleayanum） uses at least 13 host-plant species from seven genera and four families （Lauraceae, Rutaceae, Winteraceae, and Monlmiaceae）. Our larval feeding assays with G. m. moggana from Tasmania showed that certain Magnoliaceae and Lauraceae could support some larval growth to pupation. However, such growth was slower and survival was lower than observed on their normal southern sassafras host （Monimiaceae）. We also found that toxicity of particular plant species varied tremendously within plant families （for both the Magnoliceae and the Monlmiaceae）.     

Response of Soybean Canopy Photosynthesis to CO2 Concentration, Light, and Temperature

Photosynthetic rates of outdoor-grown soybean (Glycine max L.Merr. cv. Bragg) canopies increased with increasing CO₂ concentrationduring growth, before and after canopy closure (complete lightinterception), when measured over a wide range of solar irradiancevalues. Total canopy leaf area was greater as the CO₂ concentrationduring growth was increased from 160 to 990 mm³ dm^–3.Photosynthetic rates of canopies grown at 330 and 660 mm³ CO₂dm^–3 were similar when measured at the same CO₂ concentrationsand high irradiance. There was no difference in ribulose bisphosphatecarboxylase/oxygenase (rubisco) activity or ribulose 1,5-bisphosphate(RuBP) concentration between plants grown at the two CO₂ concentrations.However, photosynthetic rates averaged 87% greater for the canopiesgrown and measured at 660 mm³ CO₂ dm^–3. A 10°C differencein air temperature during growth resulted in only a 4°Cleaf temperature difference, which was insufficient to changethe photosynthetic rate or rubisco activity in canopies grownand measured at either 330 or 660 mm³ CO₂ dm^–3. RuBP concentrationsdecreased as air temperature during growth was increased atboth CO₂ concentrations. These data indicate that the increasedphotosynthetic rates of soybean canopies at elevated CO₂ aredue to several factors, including: more rapid development ofthe leaf area index; a reduction in substrate CO₂ limitation;and no downward acclimation in photosynthetic capacity, as occurin some other species. Key words: CO₂ concentration, soybean, canopy photosynthesis     

Selection by humans searching for computer- generated prey images: the effect of prey density

We investigated the effect of 'prey' density on frequency-dependent selection by human 'predators'. Eighty subjects were presented with computer-generated populations of two cryptically coloured characters on the screen of a colour monitor. Each subject was given the prey at a single combination of one of two frequencies and one of five densities, and was instructed to delete the prey as fast as possible with a light-pen. The results suggested that the degree of selection was inversely proportional to prey density, but there was no evidence that any frequency-dependent component of selection was affected.     

The response of spring barley and winter wheat to Avena fatua population density

Populations of Avena fatua were established in crops of spring barley and winter wheat, and relationships derived between yield and other crop parameters, and weed density. Competitive effects of A. fatua, which were similar to those found in other countries, were greatest at low crop densities. Crop head numbers were reduced proportionately less than crop yield, indicating that competition was affecting other yield components. Competition increased the proportion of thin grain of barley but not of wheat. Competition had little effect on the moisture content and the contamination of the harvested grain by A. fatua, suggesting that at threshold populations these factors are unlikely to be of economic significance. It was concluded that at average crop densities, low infestations of A. fatua are likely to result in cereal yield losses in the region of 1 % for each A. fatua plant m^-2.     

Thinking with Animals: New Perspectives on Anthropomorphism

Thinking with Animals: New Perspectives on Anthropomorphism. Lorraine Daston and Gregg Mitman, eds. New York: Columbia University Press, 2005. 230 pp.     

Rethinking Commodification: Cases and Readings in Law and Culture

Rethinking Commodification: Cases and Readings in Law and Culture . Martha M. Ertmanand Joan C. Williams, eds. New York. New York University Press, 2005. 450 pp.     

Effects of environment and host on vector biology and incidence of two whitefly-spread diseases of legumes in Nigeria

Seasonal periodicity in the incidence of cowpea golden mosaic (CGM) and lima bean golden mosaic (LBGM), two whitefly-spread virus-like diseases, corresponded closely with fluctuations in population density of their vector, Bemisia tabaci, at two contrasting sites in southern Nigeria. Peak catches of the vector followed the onset of rains after very high temperatures during the dry season; populations declined abruptly with continuous, heavy rainfall. At Onne, B. tabaci infested legumes at emergence and remained and reproduced on them but at Ibadan infestation was delayed and there was no evidence of reproduction on legumes. B. tabaci preferred LBGM-susceptible lima beans (Phaseolus lunatus) to resistant ones and more pupae of B. tabaci occurred on CGM-susceptible cowpea (Vigna unguiculata) cultivars than on resistant ones but these observations did not relate to the yellow-sensitivity of whiteflies. Resistance to CGM in cowpea, and to LBGM in lima bean, was identified amongst germplasm exposed to natural infection. Resistance was, in each case, associated with lower disease incidence, slower spread and milder expression of symptoms relative to susceptible cultivars. Vector non-preference for resistant cultivars may have contributed to reduced secondary spread.     

Patterns of arbuscular mycorrhiza down the profile of a heavy textured soil do not reflect associated colonization potential

Colonization of roots by arbuscular mycorrhizal (AM) fungi in several annual crops in two consecutive seasons was compared with, in the second season, the density of fungal propagules in the soil with the use of a bioassay. Root density decreased down the soil profile in both years in all crops, and a high proportion of roots were mycorrhizal throughout the profile. AM colonization decreased down the profile in cotton and lablab in the second season only. The bioassay indicated that most propagules of AM fungi in soils under cotton were located near the surface, with virtually no propagules at 1 m. The absence of propagules at depth indicates a lack of mycelium deep in the soil, and suggests that mycorrhizas are primarily initiated in the surface soil and that the fungi colonize the root system mostly through secondary spread down the profile. The use of AM colonization in the field as an indicator of propagule density and symbiotic function should be qualified by an understanding of the depth in the soil from which roots were extracted.     

Biomass and carbon accumulation in a fire chronosequence of a seasonally dry tropical forest

Seasonally dry tropical forests (SDTF) are a widely distributed vegetation type in the tropics, characterized by seasonal rainfall with several months of drought when they are subject to fire. This study is one of the first attempts to quantify above- and belowground biomass (AGB and BGB) and above- and belowground carbon (AGC and BGC) pools to calculate their recovery after fire, using a chronosequence approach (six forests that ranged form 1 to 29 years after fire and mature forest). We quantified AGB and AGC pools of trees, lianas, palms, and seedlings, and BGB and BGC pools (Oi, Oe, Oa soil horizons, and fine roots). Total AGC ranged from 0.05 to nearly 72 Mg C ha⁻¹, BGC from 21.6 to nearly 85 Mg C ha⁻¹, and total ecosystem carbon from 21.7 to 153.5 Mg C ha⁻¹; all these pools increased with forest age. Nearly 50% of the total ecosystem carbon was stored in the Oa horizon of mature forests, and up to 90% was stored in the Oa-horizon of early successional SDTF stands. The soils were shallow with a depth of <20 cm at the study site. To recover values similar to mature forests, BGC and BGB required <19 years with accumulation rates greater than 20 Mg C ha⁻¹ yr⁻¹, while AGB required 80 years with accumulation rates nearly 2.5 Mg C ha⁻¹ yr⁻¹. Total ecosystem biomass and carbon required 70 and 50 years, respectively, to recover values similar to mature forests. When belowground pools are not included in the calculation of total ecosystem biomass or carbon recovery, we estimated an overestimation of 10 and 30 years, respectively.