CETACEANS OF THE WESTERN TROPICAL INDIAN OCEAN: DISTRIBUTION, RELATIVE ABUNDANCE, AND COMPARISONS WITH CETACEAN COMMUNITIES OF TWO OTHER TROPICAL ECOSYSTEMS

We conducted a cetacean survey in the pelagic western tropical Indian Ocean (WTIO) aboard an 85-m research vessel from March to July 1995, covering 9,784 linear km. Using 25 × binoculars and line-transect methods, we recorded 589 sightings of 21 species. Stenella longirostris was the most abundant cetacean, in terms of number of individuals sighted, by an order of magnitude above any other species, while Physeter macrocephalus was the most frequently sighted, in terms of number of schools. Twelve species were widespread, seven were rare, and two were localized; our sightings include new distributional records for 12 species. Significant observations included the following: (1) Delphinus cf. tropicalis was abundant off the coast of Oman (16 sightings) and readily distinguishable in the field from D. delphis and D. capensis, (2) Balaenoptera musculus was fairly common and localized in the area of the Maldives (17 sightings), and (3) three sightings were made of an unidentified bottlenose whale tentatively referred to as Indopacetus (i. e., Mesoplodon) pacificus. We recorded 26 mixed-species cetacean schools, 43 schools with which seabirds associated, and 17 schools associated with tuna. Notable among these were mixed aggregations of Stenella attenuata, S. longirostris, yellowfin tuna, and seabirds. The cetacean community of the WTIO was similar to that of the eastern tropical Pacific (ETP) and the Gulf of Mexico (GM) in several respects. First, differences in abundance rank of individual species were small, with the result that common species were common and rare species were rare, regardless of ocean. Second, these differences in abundance were due primarily to differences in encounter rate, which varied with ocean by as much as 3,000%, and less so to school size, which generally varied less than 100%. Third, regardless of ocean, three species comprised the majority of cetaceans in the community, Stenella attenuata, S. longirostris, and S. coeruleoalba, representing 62%-82% of all individuals for all species. However, the rank order of abundance for these three species differed with ocean. Most notably, S. attenuata was abundant in the ETP and GM (abundance rank = 2 and 1, respectively) but much less common in the WTIO (abundance rank = 6). Although habitat preferences for S. attenuata appear to overlap considerably with those of S. longirostris in the ETP, our results suggest there may actually be significant differences between these two species. Detailed analysis of oceanographic correlates of distribution will be necessary in order to understand fully the habitat requirements of these pelagic dolphins, often the most conspicuous elements of tropical cetacean communities around the world.     

Land use and life history limit migration capacity of eastern tree species

Aim

Temperate tree species overwhelmingly responded to past climate change by migrating rather than adapting. However, past climate change did not have the modern human‐driven patterns of land use and fragmentation, raising questions of whether tree migration will still be able to keep pace with climate. Previous studies using coarse‐grained or randomized landscapes suggest that dispersal may be delayed but have not identified outright barriers to migration. Here, we use real‐world fragmented landscapes at the scale of forest stands to assess the migration capacity of eastern tree species.

Location

Eastern U.S.A.

Time period

Present day to 2100.

Major taxa studied

Eastern U.S. trees.

Methods

We simulated dispersal over 100 years for 15 species common to the mid‐Atlantic region and that are predicted to gain suitable habitat in the northeast. In contrast to previous studies, we incorporated greater realism with species‐specific life histories and real‐world spatial configurations of anthropogenic land use. We used simulation results to calculate dispersal rates for each species and related these to predicted rates of species habitat shift.

Results

Our simulations suggest that land use in the human‐dominated east‐coast corridor slows species dispersal rates by 12–40% and may prevent keeping pace with climate. Species most impacted by anthropogenic land use were often those with the highest predicted species habitat shifts. We identified two major dispersal barriers, the Washington DC metropolitan area and central NY, that severely impeded tree migration.

Main conclusions

Patterns of anthropogenic land use not only slowed migration but also resulted in effective barriers to dispersal. These impacts were exacerbated by tree life histories, such as long ages to maturity and narrow dispersal kernels. Without intervention, the migration lags predicted here may lead to loss in biodiversity and ecosystem functions as current forest species decline, and may contribute to formation of novel communities.     

甘肃洮河流域种子植物区系的初步研究

甘肃洮河流域地黄土高原和青藏高原的交汇地带,植物种类比较丰富,据初步统计,有种子植物１００科,４４８属,１３４６种,其种子植物区系具有下列基本特征;种类组成比较丰富,地理成分复杂,联系广泛,但以温带成分占绝对优势,具典型的北温带性质,区系成分过渡性强。根据特有种的分布情况和自然地理特征,洮河中上游植物区系应地横断山脉地区川西北,甘南,青东南地区,洮河下游应属于华北地区黄土高原亚地区。     

Resolution of the taxonomic status of Chilean and Californian jack mackerels using mitochondrial DNA sequence

Phylogeographic reconstructions using mitochondrial DNA sequences from both the control region and the cytochrome b gene demonstrated that two disjunct populations be recognized as Trachurus murphyi and Trachurus symmetricus. The species have been isolated for at least 250 000 years.     

陇东黄土高原丘陵沟壑区天然草地植物多样性研究

以陇东黄土高原丘陵沟壑区天然草地30个植被样点的样方资料为依据,以相对生物量为指标,对该地区群落植物多样性进行了研究。结果表明,该地区天然草地可划分为长芒草草原、次生杂类草草原和杂类草草甸草原3个植被类型,16个群落按放牧程度分为禁牧草地、轻牧草地和过牧草地3个层次。多样性指数显示草甸草原>长芒草草原>次生杂类草草原,轻牧草地>禁牧草地>过牧草地的趋势。放牧程度可能是影响该区域天然草地植物多样性的关键因素,出现海拔增高和降水增加多样性指数降低的趋势可能是放牧干扰的结果。相关性分析显示物种的Shannon-wiener和Simpson多样性指数与Shannon和Simpson均匀度指数间均呈显著正相关,而与生物量之间呈显著负相关。     

辽东山区次生林乔木幼苗组成及其年际动态

为了解辽东山区次生林乔木幼苗组成及其年际动态, 本文以4 ha动态监测样地为平台, 对样地内1,600个 5 m × 5 m样方进行监测。依据2014-2016年连续3年的调查, 对样地内乔木幼苗的组成、高度分布、新增和死亡年际动态、空间分布格局等进行分析。结果表明: (1)调查期间共记录到22种乔木幼苗, 3年间幼苗组成没有发生变化, 但各个样方间出现极大差异, 并且幼苗优势树种组成与样地内优势树种成分保持着一定的相似性。(2)幼苗数量在不同树种和年际间表现出较大的差异: 花曲柳(Fraxinus rhynchophylla)、色木槭(Acer mono)、胡桃楸(Juglans mandshurica)在3年间幼苗数量最多, 占幼苗总数的75.6%; 花曲柳和胡桃楸幼苗数量表现出较明显的年际波动, 其他树种波动较小, 不同树种的幼苗密度差异很大。(3)幼苗新增和死亡存在明显的种间和年际差异: 2014-2015年间幼苗的新增数量(3,888)明显高于2015-2016年间(1,710), 同时2014-2015年间幼苗死亡率(23.7%)也明显高于2015-2016年间(12.7%)。对2015-2016年间新增幼苗和已有幼苗的死亡情况进行比较可以发现, 新增幼苗总体死亡率(18.8%)明显高于已有幼苗(8.1%)。(4)对比幼苗和大树的空间分布可以发现, 样地内优势幼苗都表现出集群分布的特征。在空间分布上, 幼苗与母树保持一定的相似性。     

Population estimates of the breeding birds of the Tinhosas islands (Gulf of Guinea), the only major seabird colony of the eastern tropical Atlantic

The Tinhosas islands, in São Tomé e Príncipe, host the most important seabird breeding colony in the Gulf of Guinea, but information on its conservation status was hitherto unpublished or anecdotal, the last assessment having been performed in 1997. A two-day expedition to the Tinhosas islands was undertaken to estimate the status of breeding seabirds in 2013. Four of the five seabird species known to breed in São Tomé e Príncipe, namely Brown Booby Sula leucogaster, Sooty Tern Onychoprion fuscatus, Brown Noddy Anous stolidus and Black Noddy Anous minutus, occur on the Tinhosas. A decrease of 80% in Brown Booby numbers, possibly due to occasional exploitation, and a 30% increase in Sooty Tern and Black Noddy numbers, were found compared to 1997 data although survey methods differed. Breeding of Brown Noddy and Madeiran Storm-petrel Hydrobates castro remains unconfirmed. Our estimates confirmed that BirdLife International Important Bird and Biodiversity Area criteria are met for at least one species, the Sooty Tern. The islands are not legally protected, nonetheless, apart from moderate levels of disturbance by fishermen who land on Tinhosa Grande, no alien species were seen, and no immediate threats to the Tinhosas colony were detected. Multiple visits within and between years are recommended, to census breeders, monitor threats and establish breeding phenologies.