Geographic variation in nest-defence behaviour of the Red-tailed Hawk Buteo jamaicensis

A close fit was found between the number of years since European settlement and the call and dive-rates of Red-tailed Hawks. Call-rates were highest in the most recently settled sites.     

Matching thirty years of ecosystem monitoring with a high resolution microfossil record

1. Monitoring of the ecosystem of Lake Mývatn, Iceland, since 1975 has revealed extreme fluctuations in important food web components, such as chironomids and cladocerans, with amplitudes of several orders of magnitude and a period of 5–8 years. This study uses sediment cores from the lake to examine if the food web fluctuations appear in the microfossil record of the sediment. 2. Dating was achieved by means of a combination of ¹³⁷Cs and volcanic tephra and was fine‐tuned by wiggle‐matching of chironomid microfossil and monitoring data. 3. Cladocera exuviae and chironomid egg capsules in the uppermost 34 cm of sediment were compared with the monitoring record that consisted of 30 years of window trap catches of flying chironomids and a 16‐year record of chydorid Cladocera caught in activity traps. 4. The observed chironomid and cladoceran population fluctuations were reflected in the sediment record of chironomid eggs and of the exuviae of three of seven cladocerans: Alonella nana, Alona rectangula and Eurycercus lamellatus, which also had the most extreme fluctuations in the monitoring data (3–4 orders of magnitude). Chydorus sphaericus, and to some extent Alona quadrangularis and Acroperus harpae, showed regular fluctuations in the core that the monitoring did not reveal. Density of subfossil chironomid eggs correlated positively with that of larval head capsules but not with other microfossils. 5. This study shows a reasonably good correspondence between the fossil records of chironomids and cladocerans on the one hand and biomonitoring data on the other. The results pave the way for an extension of the food web history to much earlier time intervals of the ecosystem, allowing the study of long‐term variation in the food web dynamics, including the impact of climatic variation and other external forcing. The results also indicate the usefulness of chironomid egg capsules in palaeolimnological studies.     

Fire tolerance of perennial grass tussocks in a savanna woodland

Grass populations in tropical savannas are highly resilient in relation to different fire regimes, but the mechanisms conferring such resilience have been poorly studied. Here we examine one such mechanism, high adult survival during fire, for three perennial grass species in an Australian savanna: Eriachne triseta Nees ex Steud, Eriachne avenacea R.Br and Chrysopogon latifolius S.T.Blake. The study examined survivorship after 3 years, at plots subject to experimental fire regimes (experiencing 0, 1, 2 or 3 fires over the study period) at the Territory Wildlife Park near Darwin in the Northern Territory, Australia. Mean survivorship was 79.9%, 64.3% and 62.0% for E. avenacea, E. triseta and C. latifolius respectively. For the two species of Eriachne, mean survivorship was highest (E. avenacea, 94.6%; E. triseta, 77.1%) in unburnt plots, whereas survivorship of C. latifolius was highest (71.7%) under highest fire frequency. However, variation in survivorship among fire regime treatments was not statistically significant for any of the study species. This negligible difference in survivorship among regimes points to fire tolerance (sprouting ability) as an important mechanism contributing to the resilience and persistence of perennial grasses in these savannas.     

马尾松毛虫成虫性引诱的初步观察

马尾松毛虫(Dendrolimus punctatus Walker)在我国分布广,每年发生代数多,严重威胁松林的生长(蔡邦华,1960)。虽然飞机药剂防治能够缩短防治时间,节省人力,提高杀虫率,但还存在一些问题,为了进一步寻找新的、高效、经济、安全的防治手段,鉴于利用性引诱剂防治害虫,一方面既有可能提高杀虫药剂的使用效率,降低药剂的使用量,缩小污染范围,解决残毒的问题,而另一方面,借助性引诱剂对害虫繁殖潜力的破坏作用(Beroza,1971; Shorey ＆ Gaston,1967;Stevens ＆     

Regulation of Apical Dominance by Ethephon, Irradiance and CO2

Apical dominance of intact pea plants (Pisum sativum L. cv. Alaska) was found to be diminished by high irradiance and by increasing the CO₂ content of the air. Ethephon treatment of young plants resulted in an outgrowth of laterals, but this was significant only when the apical dominance already was weakened by high irradiance and/or CO₂.