Body temperatures of Namib Desert tenebrionid beetles: their relationship in laboratory and field

Abstract The body temperatures of six apterous species of Namib Desert tenebrionid beetles were measured continuously with indwelling thermocouples under laboratory conditions and in the field. The range of body temperatures selected was within the upper half of their 'tolerated range', which we defined as the temperatures lying between measured critical thermal maximum and critical thermal minimum. In the field, individuals also maintained their body temperatures within the upper half of the 'tolerated range'. These beetles maintained higher body temperatures than those recorded for any other ectothermic insect. Three of the six species maintained lower body temperatures in the field than they selected in the laboratory. The other three species showed no significant difference between field and laboratory body temperatures. We conclude that these beetles are not forced by biotic or abiotic factors to adopt thermal niches which present them with physiological difficulties.     

A comparison of daphnid gut particles with the sestonic particles present in two Thames Valley reservoirs throughout 1970 and 1971

The numerically most abundant component of the seston in two of the Thames Valley storage reservoirs of the Metropolitan Water Board consisted of flocculent organic material which, together with the hyaline, transparent and blackened particles, formed the non-living sestonic fraction. The abundance of bacterio-plankton was estimated from plate counts which are known to provide an under-estimate of the bacteria present. The phytoplankton consisted of the larger flagellates present throughout the year together with a seasonal succession of algae in much greater numbers, namely the smaller flagellates, diatoms, colonial greens, Tribonema and Anabaena. A seasonal analysis of the gut contents of Daphnia magna, D. pulex and D. hyalina (occurring as important grazers in the reservoirs), revealed the presence of organic particles throughout the year plus cells or filaments of the prevailing alga at different seasons. During the summer, there were periods when the guts contained recognizable animal and plant debris. Flagellate and bacterial remains were never seen intact in the guts although these were abundant in the seston during early spring. The filamentous Tribonema was ingested when large crops of it were present. The most frequent size of ingested particle was between 1–2 μm and up to 60% of the animals examined contained particles which were neither longer nor wider than 20μm. Most of these animals ranged between 0·5–1·9 mm in length. A limiting factor for ingestion was thought to be width rather than length of particle and most very large particles found in the gut were long narrow and pliant filaments like Tribonema, or gelatinous colonial green algae, or flexible, foldable crustacean filtering limbs. There appeared to be no difference in the nature or size of particle ingested by the three different species of daphnids and any difference in maximal particle width observed was more likely to be related to body size than to species of consumer.     

Uneven Rates of Landscape Change as a Source of Bias in Roadside Wildlife Surveys

ABSTRACT Roadside survey data have been used frequently to assess species occurrence and population trends and to establish conservation priorities. However, most studies using such data assume that samples are representative of either the amount of habitat or its rate of change at larger spatial scales. We tested both of these assumptions for the Breeding Bird Survey (BBS) from 1974 to 2001 in New Brunswick, Canada. Our study focused on mature forest—a cover type that we predicted would be characterized by rapid change due to human activities and that is of high ecological importance. We also sought to determine whether land cover changes adjacent to BBS routes were related to bird population trends detected in BBS data. Within all 3 time periods examined (1970s, 1980s, and 1990s), the amount of mature forest adjacent to BBS routes was significantly lower than in surrounding 1° blocks of latitude and longitude. This could be problematic for studies that use roadside data to compare the relative abundance of species. On average, mature forest declined at a rate of-1.5% per year over the 28-year study period. We detected no significant difference in the rate of change between degree blocks and BBS routes over this time span. However, in the 1970s and 1980s, mature forest declined more rapidly in degree blocks (-2.7%/yr) than adjacent to BBS routes (-0.5/yr). We also found that the BBS trend for a mature forest-associated species, blackburnian warbler (Dendroica fusca), was correlated with the trend in mature forest along BBS routes. This, combined with slower rates of mature forest change along routes in the 1970s and 1980s, suggests that BBS data may have underestimated population declines during this period. It is important that research be conducted to test for potential biases in roadside surveys caused by uneven rates of landscape change, particularly in regions characterized by rapid habitat alteration.     

Interactions between ants and seeds of two myrmecochorous plant species in recently burnt and long‐unburnt forest sites

Myrmecochory (seed dispersal by ants) is a common seed dispersal strategy of plants in fire‐prone sclerophyll vegetation of Australia, yet there is little understanding of how fire history may influence this seed dispersal mutualism. We investigated the initial fate of seeds of two myrmecochorous plant species, the small‐seeded Pultenaea daphnoides J.C. Wendl. and the large‐seeded Acacia pycnantha Benth., in replicated burnt (3.25 years since fire) and unburnt (53 years since fire) forest plots in the Mount Lofty Ranges, South Australia. Specifically we measured (i) seed removal rates; (ii) the frequency of three ant–seed interactions (seed removal, elaiosome robbery and seed ignoring); (iii) the relative contribution of different ant species to ant–seed interactions; and (iv) the abundance of common interacting ant species. Rates of seed removal from depots and the proportion of seeds removed were higher in recently burnt vegetation and the magnitude of these effects was greater for the smaller‐seeded P. daphnoides. The overall proportion of elaiosomes robbed was higher in unburnt vegetation; however, the decrease in elaiosome robbery in burnt vegetation was greater for P. daphnoides than for A. pycnantha. Ants ignored seeds more frequently in burnt vegetation and at similar rates for both seed species. In total, 20 ant species were observed interacting with seeds; however, three common ant species accounted for 66.3% of ant–seed interactions. Monomorium sydneyense almost exclusively robbed elaiosomes, Rhytidoponera metallica typically removed seeds and Anonychomyrma nr. nitidiceps showed a mix of the three behaviours towards seeds. Differences in the proportions of seeds removed, elaiosomes robbed and seeds ignored appeared to be largely driven by an increase in abundance of A. nr. nitidiceps and a decrease in abundance of M. sydneyense in burnt vegetation. Understanding how these fire‐driven changes in the initial fate of myrmecochorous seeds affect plant fitness requires further investigation.     

Can increased niche opportunities and release from enemies explain the success of introduced Yellowhammer populations in New Zealand?

Some introduced species succeed spectacularly, becoming far more abundant in their introduced than in their native range. 'Increased niche opportunities' and 'release from enemy regulation' are two hypotheses that have been advanced to explain the enhanced performance of introduced species in their new environments. Using an introduced bird species, the Yellowhammer Emberiza citrinella , which was first released in New Zealand in 1862, as a model, we tested some predictions based on these hypotheses. By quantifying habitat availability and quality, and measuring nest predation rates, we investigated whether increased niche opportunities or release from nest predation could explain the higher density of the Yellowhammer in New Zealand farmland, compared to farmland in their native Britain. Yellowhammer territory densities were over three times higher in New Zealand (0.40 territories per ha) than in comparable British farmland (0.12 territories per ha), and Yellowhammer densities remained significantly higher in New Zealand, after accounting for differences in habitat availability. The density and diversity of invertebrates, a key food resource for nestling Yellowhammers, was significantly lower in New Zealand than in Britain. Hence, these aspects of niche availability and quality cannot explain the higher density of Yellowhammers in New Zealand. Nest predation rates in New Zealand were similar to those in Britain, suggesting that release from nest predation also could not account for the higher density of Yellowhammers in New Zealand. Differences in winter survival, due to differences in winter food supply or the severity of the winter climate, along with release from other types of 'enemy' regulation are possible alternative explanations.     

Wave-induced shear stresses, plant nutrients and chlorophyll in seven shallow lakes

1. Sediment resuspension dynamics were investigated in relation to changes in water column nutrients (TP, TN, PO₄-P, NO₃-N and NH₄-N), chlorophyll a and phaeopigment in seven shallow ( Z _m < 1.5 m) lakes in South Island, New Zealand, ranging in area from 0.1 to 180 km².
2. Benthic shear stress, calculated from wind speed, effective fetch and depth, was a considerably better predictor of nutrient and pigment concentrations than wind speed.
3. For TP, TN, chlorophyll a and phaeopigment, sixteen of the possible twenty-eight linear correlations with benthic shear stress were significant at P < 0.05, with 16–87% of the variation being explained by shear stress.
4. Wind decreased the ratios of TN : TP, with ratios exponentially approaching those of the sediments as shear stress increased in four of the lakes.
5. Relationships of dissolved inorganic nutrients to shear stress were considerably weaker than those for total nutrients and showed no consistent trend over the seven lakes.
6. Estimated annual mean TP inclusive of resuspension was over four times higher than that derived from measured calm samples in two lakes.
7. The number of nutrient and pigment parameters that were significantly correlated with shear stress and the strengths of the relationships varied widely from lake to lake. We could establish no simple relationships between these effects and any single characteristic of the lake, sediment, or water.
8. A function is developed to predict the rate of entrainment of TN and TP in response to an applied shear stress, where the independent variables are sediment nutrient content and particle size, and the macrophyte density in the lake.