Neogene marine transgressions, palaeogeography and biogeographic transitions on the Thai–Malay Peninsula

Aim The aim of this review is to contribute to our understanding of the origination of the Sundaic and Indochinese biotas in Southeast Asia. Numerous unsolved problems surround the origination of the differences between these biotas and the determinants of the breadth and current position of the transition between them. Location Literature reviews show that phytogeographical and zoogeographical transitions between the Sundaic and Indochinese subregions lie on the Thai–Malay peninsula just north of the Isthmus of Kra. A second, more widely recognized botanical transition lies 500 km further south at the Kangar–Pattani line near the Thai–Malay border. Results The phytogeographical transition involves 575 genera of plants, and a change from wet seasonal evergreen dipterocarp rain forest to moist mixed deciduous forest. The zoogeographical transition is best characterized for forest birds, and more than half the species present in this region have species boundaries north of the Isthmus of Kra, at 11–13° N latitude. Although the phytogeographical transition is climate‐related today, and the avifaunal transition is viewed as being associated with the vegetation change, there is no obvious present day geological, physiographical or environmental feature to account for the origination of the provincial biotas. Similarly, known Neogene palaeoenvironmental changes on the tectonically stable peninsula, including those associated with periods of lower sea levels and the emergence of Sundaland, fail to account for either the origination of the provincial differences or the current position of the transition. Main conclusions Contrary to earlier palaeogeographical reconstructions, it is suggested that Neogene marine transgressions flooded the peninsula in two areas and created circumstances leading to the biogeographical patterns of the present day. The Vail global eustatic curve, supported by the oxygen isotope record, indicates that sea levels were c. 100 m above the present‐day level during the early/middle Miocene (24–13 Ma) and again during the early Pliocene (5.5–4.5 Ma). Present topography suggests such high sea stands would have created 30–100‐km wide seaways north and south of the Nakhon si Thammarat Range in the central peninsula (southern Thailand). Geological, palaeontological and phylogenetic evidence for such hypothetical seaways is scant (there have been no focussed searches) but does not preclude their occurrence. The role of such Neogene highstands in explaining present day biogeographical patterns in Southeast Asia and elsewhere requires assessment.     

The Indochinese–Sundaic zoogeographic transition: a description and analysis of terrestrial mammal species distributions

Aim We describe the distributions of mammal species between the Indochinese and Sundaic subregions and examine the traditional view that the two faunas show a transition near the Isthmus of Kra on the Thai–Malay peninsula. Location Species distributions are described along a 2000‐km transect from 20° N (northernmost Thailand) to 1° N (Singapore). Methods For the 325 species of native non‐marine mammals occurring along the transect we used published records to provide a database of their distributional records by degree of latitude. Results Along the transect we found 128 Indochinese species with southern range limits, 121 Sundaic species with northern range limits, four un‐assignable endemics and 72 widespread species. In total, 152 southern and 147 northern range limits were identified, and their distribution provides no evidence for a narrow faunal transition near the Isthmus of Kra (10°30′ N) or elsewhere. Range limits of both bats and non‐volant mammals cluster in northernmost peninsular Malaysia (5° N) and 800 km further north, where the peninsula joins the continent proper (14° N). The clusters of northern and southern range limits are not concordant but overlap by 100–200 km. Similarly, the range limits of bats and non‐volant mammals cluster at slightly different latitudes. There are 30% fewer species and range limits in the central and northern peninsula (between 6 and 13° N), and 35 more widely distributed species have range gaps in this region. In addition, we found 70 fewer species at the southern tip of the peninsula (1° N) than at 3–4° N. Main conclusions The deficiencies of both species and species range limits in the central and northern peninsula are attributed to an area effect caused by repeated sea‐level changes. Using a new global glacioeustatic curve developed by Miller and associates we show that there were > 58 rapid sea‐level rises of > 40 m in the last 5 Myr that would have resulted in significant faunal compression and local population extirpation in the narrow central and northern parts of the peninsula. This new global sea‐level curve appears to account for the observed patterns of the latitudinal diversity of mammal species, the concentration of species range limits north and south of this area, the nature and position of the transition between biogeographical subregions, and possibly the divergence of the faunas themselves during the Neogene. The decline of species diversity at the southern end of the transect is attributed to a peninsula effect similar to that described elsewhere.     

A new Ansonia from the Isthmus of Kra, Thailand (Amphibia, Anura, Bufonidae)

A new species of torrent-dwelling bufonid frog of the genus Ansonia is described from the Isthmus of Kra, Thailand. Ansonia kraensis is morphologically similar to Malaysian A. malayana, but differs from it in ventral coloration and larval morphology. Occurrence of A. kraensis in this region suggests a heterogeneous nature of the anuran fauna between northern and southern regions of the Malay Peninsula.     

基因组时代的新视野: 东南亚哺乳动物类群在第四纪冰河时期多样性的起源与分化

东南亚地区东起菲律宾群岛, 西至印度次大陆, 北及中国中部, 南至巽他群岛, 涵盖了世界上25个最重要的生物多样性热点地区之中的6个, 具有极其重要的全球生物多样性保护的战略意义。该地区复杂的地质地貌和气候历史使其动植物的种类和数量都极为丰富。经典的生物地理分界线华莱士线和克拉地峡将该地区进一步划分出包括部分巽他群岛和马来半岛在内的南部巽他区和北部印度支那区两个生物多样性热点地区。主要基于形态学的生物地理学研究认为巽他区和印度支那区通过马来半岛陆地相连, 并且第四纪大部分时间海平面下降形成大陆桥, 直到一万年前该地区的众多岛屿仍与大陆连接, 促进了哺乳动物的种群迁徙与基因交流, 因此物种种群间的差别将很细微。然而近来分子遗传学研究表明, 由于其他生态因素制约, 哺乳动物的迁移能力可能比以往认为的低, 大陆桥的存在并不一定导致迁徙的发生, 许多种群的隔离早在200万年前便已形成, 并且没有因为后来冰川期海平面降低而恢复种群交流, 而距今7.3万年前发生的苏门答腊多巴超级火山爆发也可能进一步影响了物种间和物种内多样性的形成和分化。通过已有的东南亚哺乳动物种群遗传学研究结果, 我们认为物种间或种群间的差异主要表现为三个层次: 巽他区种群与印度支那区种群间约百万年尺度的分化, 巽他区不同岛屿种群间约数十万年尺度的分化, 以及发生于晚更新世的分化事件。已有的东南亚种群遗传学研究主要采用线粒体及核基因多位点数据进行分析, 而种群基因组学分析则使得获得详尽的种群历史动态成为可能, 并使我们可以进一步了解东南亚哺乳动物类群所经历的物种形成过程。     

Phylogeographic evidence for the existence of an ancient biogeographic barrier: the Isthmus of Kra Seaway

Biogeographic boundaries are characterised by distinct faunal and floral assemblages restricted on either side, but patterns among groups of taxa often vary and may not be discrete. Historical biogeography as a consequence, while providing crucial insights into the relationship between biological diversity and earth history, has some limitations. Patterns of intraspecific molecular variation, however, may show unambiguous evidence for such historical divides, and can be used to test competing biogeographic hypotheses (often based on the dispersal-vicariance debate). Here, we utilise this method to test the hypothesis that a major biogeographic transition zone between the Sundaic and Indochinese biotas, located just north of the Isthmus of Kra in SE Asia, is the result of Neogene marine transgressions that breached the Isthmus in two locations for prolonged periods of time (>1 million year duration). Phylogeographic analyses of a freshwater decapod crustacean, the giant freshwater prawn Macrobrachium rosenbergii, strongly supports the historical existence of the more northerly postulated seaway. Results presented here highlight the power of utilising intraspecific molecular variation in testing biogeographical hypotheses.     

Explaining the causes of the zoogeographic transition around the Isthmus of Kra: using bats as a case study

Aim  The causes of a zoogeographic divide in peninsular Thailand around the Isthmus of Kra have not been adequately resolved. We explored climatic, historical and geological perspectives to gain insights into factors that may have contributed to the development and maintenance of this zoogeographic transition, and to determine whether a faunal transition occurs for bats. Location  Southeast Asia, focusing on the Thai Peninsula. Methods  Spatial principal components analysis was used to determine the relationship between climate and species distribution patterns. We studied bats (order Chiroptera) because of their ability to bypass small‐scale geophysical barriers. Spatial data on bat species distributions on the Thai Peninsula were analysed in relation to multivariate measures of climate to determine the possible influence of climatic zonation on distribution patterns. We assessed the effects of the interaction of climatic zonation with the highly dynamic environmental conditions the area has undergone in relation to species distribution patterns. Results  A zoogeographic transition was found, with 44 species (out of 127) restricted to the north of the Isthmus of Kra and 29 restricted to the south, although there were relatively few abrupt changes in distribution at the exact position of the isthmus. Northern and southern species were associated with specific climatic conditions. Major transitions in the distribution of bat species exist at 6–6.5° N and 13–13.5° N, with a smaller peak at 11.0° N. These major peaks fall in the same areas as the borders of climatic zones, and the 6–6.5° N peak falls in the same area as a floristic divide (the Kangar–Pattani Line). Main conclusions  On the mainland, climatic zones cause gradual changes in species distributions. However, in addition to climatic factors, repeated changes in the breadth of the Sunda Shelf during recent glacial cycles may have caused locally high extinction rates at narrow points on the peninsula, exacerbating transitions in species distribution patterns along the region, in the context of a peninsula effect that reduces opportunities for recolonization.     

Heterochrony: The evolution of ontogeny. By Michael L. McKinney and Kenneth J. McNamara. New York: Plenum Press. 1991. XIX + 437 pp. ISBN 0-306-43638-8. $ 49.50 (cloth)

Macaca fascicularis is broadly distributed in Southeast Asia across 30° of latitude and 35° of longitude (Indochinese Peninsula, Isthmus of Kra, Malay Peninsula, Greater and Lesser Sunda Islands, Philippine Islands, and numerous small, neighboring islands). The range is divisible into 1) a core area comprised of mainland Southeast Asia, Borneo, Sumatra, and Java (large land masses interconnected during the last glacial maximum, 18,000 B. P.); 2) shallow-water fringing islands, which are smaller islands connected to the core area during the last glacial maximum; and 3) deep-water fringing islands, which are peripheral islands not connected to the core area during the last glacial maximum. Skull length was used to study effects of latitude and insularity on patterns of size variation. The data are from 802 adult M. fascicularis specimens from 140 core-area localities, 63 shallow-water islands, and 29 deep-water islands. Sex-specific polynomial regressions of skull length on latitude were used to describe skull length variation in the core area. These regressions served as standards for evaluating variation among samples from shallow-water and deep-water islands. The core area exhibits Bergmannian latitudinal size clines through most of the species range. Thus, skull length decreases from about 8°S (Java) to the equator (Sumatra and Borneo), then increases as far north as about 13°N (Isthmus of Kra). Farther north, to the northernmost Indochinese localities at about 17°N, skull length in M. fascicularis decreases with increasing latitude, contrary to Bergmann's rule. Latitudinal size variation in shallow-water fringing islands generally parallels that in the core area. However, skull length tends to be smaller than in the core area at similar latitudes. Deep-water fringing islands are markedly more variable, with relatively small specimens in the Lesser Sunda Islands and relatively large specimens in the Nicobar Islands. These analyses illustrate how a primate species may vary in response to latitudinal temperature variation and to isolation. © 1993 Wiley-Liss, Inc.     

Pelage Color Variation of Macaca arctoides and Its Evolutionary Implications

Stump-tailed macaques (Macaca arctoides) exhibit significant intraspecific variation in pelage color. Based on their pelage color and geographical distribution, they are classified into 2 subspecies: northern bright brown Macaca arctoides arctoides and southern black Macaca arctoides melanota. However, studies on the natural population are extremely scarce, and researchers have occasionally questioned the subspecific classification. We quantitatively examined pelage color variation of Macaca arctoides in 3 free-ranging populations in Thailand. Pelage color difference between populations is significant. The population distributed south of the Isthmus of Kra showed wide intrapopulational variation, including bright brown, dark brown, and completely black, whereas the northern populations primarily had dark brown hairs. Thus, we conclude that one cannot classify the color variants into subspecies. Further, we hypothesize that the distinctive polymorphism in southern Thailand resulted from geographical isolation caused by the Pleistocene eustatic fluctuations and subsequent recovery of land connection and subsequent gene flow.     

Boundary zone between northern and southern pig-tailed macaques and their morphological differences

Based on previous conflicting reports that the two forms of pig-tailed macaque (northern and southern) exist as separate species, subspecies, or forms, and that their boundary zone lies in Thailand, a survey of the distribution range and morphology of pig-tailed macaques in Thailand was conducted during 2003–2010. We first conducted a questionnaire survey. Questionnaires were sent to 7,410 subdistricts throughout Thailand. We then traveled to 72 of the 123 subdistricts reporting the presence of pig-tailed macaques. However, due to a lack of reports of the presence of free-ranging pig-tailed macaques living south of the Isthmus of Kra, a survey of pet pig-tailed macaques was also conducted during 16–24 September 2011. Furthermore, 35 wild northern pig-tailed macaques inhabiting northern Thailand (13°13′N, 101°03′E) were temporarily caught and their morphological characters were measured and then compared to those of the southern form captured from Sumatra, Indonesia. Although largely allopatric, the ranges of the northern and southern pig-tailed macaques in Thailand were found to have a partially sympatric boundary at the Surat Thani–Krabi depression (8–9°30′N). Morphologically, these two forms were very distinctive, with different morphological characters such as the crown patch, the white color of the triangle above the eyes, the red streak at the external rim of the eyes, pelage color, ischial callosity, tail length and carriage, facial height, and limb length in both sexes, and patterns of sex skin swelling and reddening in females. These differences in morphological characters between the northern and southern forms should help settle the problems of their taxonomy.     

Biogeographic variation in skull morphology across the Kra Isthmus in dusky leaf monkeys

Despite the growing literature on the underlying factors of geographical phenotypic variation, little is known about how and to what extent biogeographic barriers in South‐East Asia have shaped morphological variation in primates. We aimed to investigate the geographical variations in skull morphology in dusky leaf monkeys by decomposing them into clinal (latitudinal), non‐clinal spatial (discrete difference between regions north and south of the Isthmus of Kra), and environment‐related components. We applied geometric morphometrics to measure 53 adult male specimens from 36 localities, covering the regions both north and south of the Isthmus of Kra. A linear model was used to test the effects of region (north vs. south of the Isthmus of Kra), latitude, and environmental factors (temperature and rainfall) on the size and shape of skulls. A part of variation in skull shape differed moderately between the regions in the north and south of the Isthmus of Kra, and this difference cannot be explained by latitudinal and environmental factors. However, for size and the majority of variations in shape, we detected limited contributions of region and the two environmental factors. Shape differentiation that was unexplained by latitudinal and environmental factors suggests that dusky leaf monkeys may have experienced a population division due to habitat constriction around the Isthmus of Kra. However, this divergence probably has been obscured by subsequent gene flow between populations after habitat recovery.     

Theloderma licin McLeod and Ahmad, 2007 （Lissamphibia： Anura： Rhacophoridae）, a New Frog Record for Borneo

A new record of the rhacophorid frog, Theloderma licin is reported from Gunung Serambu, in the Bau region of western Sarawak, East Malaysia, which comprises the first published record of the species from the Sundaic island of Borneo. The species was previously known from the Malay Peninsula （southern Peninsular Thailand and Peninsular Malaysia）. Species of Theloderma are widespread in mainland and insular Southeast Asia, their arboreal habits perhaps contributing to our perception of rarity.     

Four new species, a new variety, and a status change in Argostemma (Rubiaceae) from Thailand

Four new species of Argostemma , all endemic to Thailand are described: A. thaithongae , restricted to northern Thailand; A. monophyllum , rather widely distributed in the easern half of Thailand: A. puffii and A. routundicalyx , both endemic to peninsular Thailand. Var. variabile is a new variety of the peninsular Thailand, species A. lobulatum. A. setosum , previously thought to be an endemic species of peninsular Thailand, is now considered to be a subspecies of A. laeve (Malay peninsula and Sumatra): A. laeve subsp. setosum , stat. nov.     

Do leaf margins of the temperate forest flora of southern South America reflect a warmer past?

Aim   Our aims were: (1) to characterize the linear relationship between the proportion of woody dicotyledonous species with entire-margined leaves ( E ) and mean annual temperature (MAT) from a southern temperate flora that still harbours many lineages that originated under warmer climates; (2) to compare this relationship with those developed from floras of different regions of the world; and (3) to contrast temperature predictions based on leaf margins of the native southern flora versus the naturalized alien flora, mostly of boreal origin.
Location   The temperate forest of southern South America (TFSA).
Methods   At each 1° latitudinal band, we estimated E based on species latitudinal ranges and MAT from both an isotherm map and a global temperature grid. We also calculated E from five local floras located between 40 and 43° S, and from the naturalized alien flora of Nahuel Huapi National Park in southern Argentina.
Results   We found a close relationship between E and MAT for the TFSA. Equations developed from floras of the Northern Hemisphere overestimated extant temperatures of this biome by 6–10 °C at both geographical and local spatial scales. On the other hand, MAT predictions from leaf margins of the alien flora were similar to the actual MAT. A published regression between E and MAT from tropical South America was remarkably similar to the one we estimated from the TFSA. This tropical equation predicted accurately the temperatures observed for this temperate biome based on leaf margins of the native flora.
Main conclusions   Despite massive plant extinction due to environmental cooling and biogeographical isolation during the Tertiary, leaf-margin analysis reveals that the flora of the TFSA still reflects its original development under the warmer conditions of western Gondwana and its past connections with low-latitude forest floras of tropical South America.     

Female long-tailed macaques with scrotum-like structure

Female long-tailed macaques (Macaca fascicularis) living in multimale and multifemale societies show a swelling and reddening of the sexual skin around the anogenital region when they approach ovulation. These swellings are limited to the base of the tail in many local populations. We recently observed another type of sexual swelling in long-tailed macaques inhabiting localities north of the Isthmus of Kra, Thailand. This swelling was located in the inguinal region in pubertal females. These swellings develop bilaterally into a globular structure, which so strongly resembles the male scrotum that it is difficult to reliably identify an individual's sex at a distance using only the standard phenotypic features of differential presence of clitoris or scrotum. The sex of the monkeys possessing the scrotum-like swelling was examined at the chromosomal and gonadal levels by determining the presence of two sex-related genes (the SRY and the AMEL), and sex-steroid hormone levels, respectively. For chromosomal sex, polymerase chain reaction (PCR)-based assays suggested the absence of the Y-linked SRY and AMEL loci but the presence of the X-linked AMEL locus in the scrotum-like monkeys, consistent with them being XX and not XY. Plasma testosterone levels of the monkeys possessing the inguinal sex skin swelling did not differ from those of ordinary females and was significantly lower than that of subadult and adult males. However, plasma estradiol levels were higher than those of both ordinary adult males and ordinary adult females. Together, the data strongly support the suggestion that these are XX females. Indeed, most of the tissue components of the scrotum-like swelling were in fact adipose cells. Upon our latest survey in Thailand, the scrotum-like swellings were observed only in long-tailed macaques inhabiting the Indochinese region, above the Isthmus of Kra. To understand whether the scrotum-like swelling is related to geographical distribution, further study is necessary.     

Range-wide phylogeography of the European temperate-montane herbaceous plant Meum athamanticum Jacq.: evidence for periglacial persistence

Aim  The aim of this study is to analyse the genetic population structure of Meum athamanticum Jacq. in order to explore the alternative hypotheses (1) that the central and northern highland populations are the result of post-glacial recolonization from southern refugia, and the disjunct distribution of M. athamanticum can be explained by modern ecological conditions, or (2) that extant populations north of the Alps and Pyrenees persisted in situ during glacial periods.
Location  Europe.
Methods  Variation of amplified fragment length polymorphisms (AFLPs) was analysed for 23 populations from the entire range of the species. We used band-based approaches and methods based on allele frequencies to measure genetic diversity and to identify population structure.
Results  Our analyses reveal a north–south differentiation within M. athamanticum . High levels of genetic diversity, as well as private fragments, are found in populations both north and south of the Alps. Differentiation among populations is lower in the northern than in the southern population group, and significant isolation-by-distance is found only in the latter group.
Main conclusions  Our results indicate that M. athamanticum survived the last ice age in multiple refugia throughout its contemporary range and did not expand into areas north of the Alps from southern refugia. We found evidence that regional-scale migration in northern, formerly periglacial, parts of the species range has resulted in the intermingling of populations. In contrast, southern populations are characterized by long-term isolation. The south-west Alps represent an area where immigration and mixing of populations from northern and southern refugia appears to have taken place.     

Geographical variation in Japan in egg development of the mayfly, Ephoron shigae (Ephemeroptera: Polymitarcyidae)

1. The effect of temperature on embryonic development was compared in four populations, two bisexual and two unisexual, of Ephoron shigae , including one each near the northern and southern periphery of the species range in Japan.
2. Eggs from every population were chilled at 4, 8 or 12 °C for diapause development after 50 days at 20 °C for pre-diapause development (experiment I). Some eggs hatched during chilling at 8 °C or 12 °C, whereas no eggs hatched at 4 °C. The rate of hatching in a given condition of chilling was higher for the eggs from warmer winter environments.
3. Chilling at 4 or 8 °C effectively facilitated diapause development. Chilling at 12 °C was, in general, not so effective, but relatively effective for the eggs from warmer winter environments.
4. Eggs were incubated at 8, 12, 15 or 20 °C after chilling at 4 °C to examine the effect of temperature on post-diapause development (experiment II). The eggs incubated at higher temperature after chilling hatched quicker and more synchronously and had higher hatching success.
5. The relationship between temperature and the days required for hatching after chilling was well described by the power function. There was no significant difference in the slope of the regression lines (i.e. temperature dependency) among local populations. However, a longer time was required for hatching at a given temperature for the population from the colder winter environment.
6. There was no detectable difference in the observed intraspecific variations between unisexual and bisexual populations.     

Sympatric Asian felid phylogeography reveals a major Indochinese–Sundaic divergence

The dynamic geological and climatological history of Southeast Asia has spawned a complex array of ecosystems and 12 of the 37 known cat species, making it the most felid‐rich region in the world. To examine the evolutionary histories of these poorly studied fauna, we compared phylogeography of six species (leopard cat Prionailurus bengalensis, fishing cat P. viverrinus, Asiatic golden cat Pardofelis temminckii, marbled cat P. marmorata, tiger Panthera tigris and leopard P. pardus) by sequencing over 5 kb of DNA each from 445 specimens at multiple loci of mtDNA, Y and X chromosomes. All species except the leopard displayed significant phylogenetic partitions between Indochina and Sundaland, with the central Thai–Malay Peninsula serving as the biogeographic boundary. Concordant mtDNA and nuclear DNA genealogies revealed deep Indochinese–Sundaic divergences around 2 MYA in both P. bengalensis and P. marmorata comparable to previously described interspecific distances within Felidae. The divergence coincided with serial sea level rises during the late Pliocene and early Pleistocene, and was probably reinforced by repeated isolation events associated with environmental changes throughout the Pleistocene. Indochinese–Sundaic differentiations within P. tigris and P. temminckii were more recent at 72–108 and 250–1570 kya, respectively. Overall, these results illuminate unexpected, deep vicariance events in Southeast Asian felids and provide compelling evidence of species‐level distinction between the Indochinese and Sundaic populations in the leopard cat and marbled cat. Broader sampling and further molecular and morphometric analyses of these species will be instrumental in defining conservation units and effectively preserving Southeast Asian biodiversity.     

Possible effects of habitat fragmentation and climate change on the range of forest plant species

Global circulation models predict an increase in mean annual temperature between 2.1 and 4.6 °C by 2080 in the northern temperate zone. The associated changes in the ratio of extinctions and colonizations at the boundaries of species ranges are expected to result in northward range shifts for a lot of species. However, net species colonization at northern boundary ranges, necessary for a northward shift and for range conservation, may be hampered because of habitat fragmentation. We report the results of two forest plant colonization studies in two fragmented landscapes in central Belgium. Almost all forest plant species (85%) had an extremely low success of colonizing spatially segregated new suitable forest habitats after c . 40 years. In a landscape with higher forest connectivity, colonization success was higher but still insufficient to ensure large-scale colonization. Under the hypothesis of net extinction at southern range boundaries, forest plant species dispersal limitation will prevent net colonization at northern range boundaries required for range conservation.     

Atmospheric nitrogen-deposition may intensify phosphorus limitation of shallow epilithic periphyton in unproductive lakes

1. We tested whether increasing atmospheric nitrogen (N) deposition along a north–south gradient intensifies epilithic phosphorus (P) limitation in oligotrophic Swedish lakes from the north to the south. We examined the epilithic community at a shallow depth from seven northern and six southern Swedish lakes, and also compared the results with a lake located geographically between the two groups. We determined lake nutrient state, epilithic nutrient ratios and epilithic algal composition, as well as grazer N : P ratios, grazer-epilithon N : P imbalance, and N : P cycling ratios.
2. Epilithic communities appear to be generally more N-limited in the northern lakes and more P-limited in the southern lakes. Lake water total N (Tot-N) and epilithic N : P ratios were lower in northern than in southern lakes and the proportion of N₂-fixing cyanobacteria was higher in northern than in southern lakes.
3. Gastropod grazers had lower N : P imbalances and cycled less N relative to P in northern than in southern lakes.
4. Atmospheric N-deposition showed a strong positive correlation with lake water Tot-N and a much weaker positive correlation with epilithon N : P ratios. Atmospheric N-deposition also correlated negatively with the proportion of N₂-fixing cyanobacteria.
5. There are indications that increased atmospheric N-deposition towards the south might intensify P-limitation of epilithic algae and invertebrate grazers, although more studies are needed to show the strength and generality of our findings.     

Geographical patterns of species turnover in aquatic plant communities

1. A classic theory in biogeography predicts that high latitude communities are unstable. This may be because of decreased species richness or decreased environmental predictability and productivity towards the poles.
2. We studied latitudinal patterns in long-term community persistence of aquatic vascular plants in 112 Finnish lakes, situated within a 1000-km range from the northernmost to the southernmost lake.
3. Contrary to theoretical predictions, we found that the turnover rate of plant species in 45 years was inversely related to latitude. That is, plant communities in northern lakes were more persistent than communities in southern lakes. When we used multiple regression to find the best predictors of species turnover rate (TR), latitude was the only variable that was highly significantly related to species turnover rate. Area, species number, water transparency, pH and change in transparency did not notably explain the gradient observed.
4. The latitudinal trend was mainly because of lower species immigration rates at higher latitudes, whereas extinction rate did not so strongly decrease with increasing latitude. Immigrations and extinctions in the lakes were not in balance: the species numbers between the 1930s and 1980s increased more strongly in the southern than northern lakes.
5. We suggest that the inverse relationship between latitude and plant species TR in Finland is most probably caused by human influence on lakes, especially eutrophication and immigration of new species in southern latitudes. In addition, although species richness per lake did not decrease towards the north, the total species pool probably does, which means that in the north there are fewer species that can actually immigrate.