Tropical Montane Regions Research Articles

Targeted protection and restoration to conserve tropical biodiversity in a warming world

Complex landscapes interact with meteorological processes to generate climatically suitable habitat (refuges) in otherwise hostile environments. Locating these refuges has practical importance in tropical montane regions where a high diversity of climatically specialized species is threatened by climate change. Here, we use a combination of weather data and spatial modeling to quantify thermally buffered environments in a regional tropical rainforest. We do this by constructing a spatial surface of maximum air temperature that takes into account important climate-mediating processes. We find a strong attenuating effect of elevation, distance from coast and foliage cover on maximum temperature. The core habitat of a disproportionately high number of endemic species (45%) is encompassed within just 25% of the coolest identified rainforest. We demonstrate how this data can be used to (i) identify important areas of cool habitat for protection and (ii) efficiently guide restoration in degraded landscapes to expand extant networks of critical cool habitat.

Patterns of persistence and isolation indicate resilience to climate change in montane rainforest lizards

Globally, montane tropical diversity is characterized by extraordinary local endemism that is not readily explained by current environmental variables indicating a strong imprint of history. Montane species often exist as isolated populations under current climatic conditions and may have remained isolated throughout recent climatic cycles, leading to substantial genetic and phenotypic divergence. Alternatively, populations may have become contiguous during colder climates resulting in less divergence. Here we compare responses to historical climate fluctuation in a montane specialist skink, Lampropholis robertsi, and its more broadly distributed congener, L. coggeri, both endemic to rainforests of northeast Australia. To do so, we combine spatial modelling of potential distributions under representative palaeoclimates, multi-locus phylogeography and analyses of phenotypic variation. Spatial modelling of L. robertsi predicts strong isolation among disjunct montane refugia during warm climates, but with potential for localized exchange during the most recent glacial period. In contrast, predicted stable areas are more widespread and connected in L. coggeri. Both species exhibit pronounced phylogeographic structuring for mitochondrial and nuclear genes, attesting to low dispersal and high persistence across multiple isolated regions. This is most prominent in L. robertsi, for which coalescent analyses indicate that most populations persisted in isolation throughout the climate cycles of the Pleistocene. Morphological divergence, principally in body size, is more evident among isolated populations of L. robertsi than L. coggeri. These results highlight the biodiversity value of isolated montane populations and support the general hypothesis that tropical montane regions harbour high levels of narrow-range taxa because of their resilience to past climate change.

Are lowland rainforests really evolutionary museums? Phylogeography of the green hylia (Hylia prasina) in the Afrotropics

A recent trend in the literature highlights the special role that tropical montane regions and habitat transitions peripheral to large blocks of lowland rainforest play in the diversification process. The emerging view is one of lowland rainforests as evolutionary ‘museums’; where biotic diversity is maintained over evolutionary time, and additional diversity is accrued from peripheral areas, but where there has been little recent diversification. This leads to the prediction of genetic diversity without geographic structure in widespread taxa. Here, I assess the notion of the lowland rainforest ‘museum’ with a phylogeographic study of the green hylia (Aves: Sylviidae: Hylia prasina) using 1132bp of mtDNA sequence data. The distribution of genetic diversity within the mainland subspecies of Hylia reveals five highly divergent haplotype groups distributed in accordance with broad-scale areas of endemism in the Afrotropics. This pattern of genetic diversity within a currently described subspecies refutes the characterization of lowland forests as evolutionary museums. If the pattern of geographic variation in Hylia occurs broadly in widespread rainforest species, conservation policy makers may need to rethink their priorities for conservation in the Afrotropics.

The Floristic Composition and Biogeographical Significance of A Megadiverse Páramo Site in The Southern Ecuadorian Andes1

The Huancabamba Biogeographical Province covers sections of southern Ecuador and northern Peru, and is well known for both its biodiversity and high levels of endemism. Páramo, a form of tropical alpine vegetation, covers less area in this region than in other tropical montane regions, and is dominated by shrubs instead of tussock grasses. A botanical inventory was conducted at a páramo site in Podocarpus National Park, southern Ecuador. Located between 3385 and 3250 m elevation, this site covers 2.4 ha of grass- and shrub-dominated vegetation communities. Fifty-five families, 90 genera and 136 species occurred, 27 of which are endemic to Ecuador. Both the combination of species and the growth forms differ markedly from those of most other páramo ecosystems. After describing the floristic characteristics of the site, I discuss the species composition, growth forms, and patterns of endemism in relation to various geographical and ecological factors.

Climatic zonation drives latitudinal variation in speciation mechanisms

Many groups of organisms show greater species richness in the tropics than in the temperate zone, particularly in tropical montane regions. Forty years ago, Janzen suggested that more limited temperature seasonality in the tropics leads to greater climatic zonation and more climatic barriers to organismal dispersal along elevational gradients in the tropics relative to temperate regions. These factors could lead to differences in how species arise in tropical versus temperate regions and possibly contribute to greater tropical diversity. However, no studies have compared the relationships among climate, elevational distribution and speciation in a group inhabiting both tropical and temperate regions. Here, we compare elevational and climatic divergence among 30 sister-species pairs (14 tropical, 16 temperate) within a single family of salamanders (Plethodontidae) that reaches its greatest species richness in montane Mesoamerica. In support of Janzen's hypothesis, we find that sister species are more elevationally and climatically divergent in the tropics than in the temperate zone. This pattern seemingly reflects regional variation in the role of climate in speciation, with niche conservatism predominating in the temperate zone and niche divergence in the tropics. Our study demonstrates how latitudinal differences in elevational climatic zonation may increase opportunities for geographical isolation, speciation and the associated build-up of species diversity in the tropics relative to the temperate zone.

Projected distributions of novel and disappearing climates by 2100 AD.

Key risks associated with projected climate trends for the 21st century include the prospects of future climate states with no current analog and the disappearance of some extant climates. Because climate is a primary control on species distributions and ecosystem processes, novel 21st-century climates may promote formation of novel species associations and other ecological surprises, whereas the disappearance of some extant climates increases risk of extinction for species with narrow geographic or climatic distributions and disruption of existing communities. Here we analyze multimodel ensembles for the A2 and B1 emission scenarios produced for the fourth assessment report of the Intergovernmental Panel on Climate Change, with the goal of identifying regions projected to experience (i) high magnitudes of local climate change, (ii) development of novel 21st-century climates, and/or (iii) the disappearance of extant climates. Novel climates are projected to develop primarily in the tropics and subtropics, whereas disappearing climates are concentrated in tropical montane regions and the poleward portions of continents. Under the high-end A2 scenario, 12-39% and 10-48% of the Earth's terrestrial surface may respectively experience novel and disappearing climates by 2100 AD. Corresponding projections for the low-end B1 scenario are 4-20% and 4-20%. Dispersal limitations increase the risk that species will experience the loss of extant climates or the occurrence of novel climates. There is a close correspondence between regions with globally disappearing climates and previously identified biodiversity hotspots; for these regions, standard conservation solutions (e.g., assisted migration and networked reserves) may be insufficient to preserve biodiversity.

The role of wood anatomy in phylogeny reconstruction of Ericales.

The systematic significance of wood anatomical characters within Ericales is evaluated using separate and combined parsimony analyses including 23 wood characters and 3945 informative molecular characters. Analyses of wood features alone result in poorly resolved and conflicting topologies. However, when pedomorphic character states are coded as inapplicable, the combined bootstrap topology results in an increase of resolution and support at most deeper nodes compared with the molecular analyses. This suggests that phylogenetic information from the limited number of morphological characters is not completely swamped by an overwhelming amount of molecular data. Based on the morphology of vessels and fibers, and the distribution of axial parenchyma, two major wood types can be distinguished within Ericales: (i) a "primitive" type, nearly identical to the wood structure in the more basal outgroup Cornales, which is likely to have persisted in one major clade, and (ii) a "derived" type that must have evolved in at least two separate evolutionary lines. The occurrence of the first type is strongly correlated with shrubs to small trees growing in cold temperate or tropical montane regions, while the second type is common in tall trees of tropical lowlands. This favors the inclusion of ecologically adaptive features in phylogeny reconstruction.

DOES NICHE CONSERVATISM PROMOTE SPECIATION? A CASE STUDY IN NORTH AMERICAN SALAMANDERS

Abstract Recent speciation research has generally focused on how lineages that originate in allopatry evolve intrinsic reproductive isolation, or how ecological divergence promotes nonallopatric speciation. However, the ecological basis of allopatric isolation, which underlies the most common geographic mode of speciation, remains poorly understood and largely unstudied. Here, we explore the ecological and evolutionary factors that promote speciation in Desmognathus and Plethodon salamanders from temperate eastern North America. Based on published molecular phylogenetic estimates and the degree of geographic range overlap among extant species, we find strong evidence for a role for geographic isolation in speciation. We then examine the relationship between climatic variation and speciation in 16 sister-taxon pairs using geographic information system maps of climatic variables, new methods for modeling species' potential geographic distributions, and data on geographic patterns of genetic variation. In contrast to recent studies in tropical montane regions, we found no evidence for parapatric speciation along climatic gradients. Instead, many montane sister taxa in the Appalachian Highlands inhabit similar climatic niches and seemingly are allopatric because they are unable to tolerate the climatic conditions in the intervening lowlands. This temporal and spatial-ecological pattern suggests that niche conservatism, rather than niche divergence, plays the primary role in promoting allopatric speciation and montane endemism in this species-rich group of vertebrates. Our results demonstrate that even the relatively subtle climatic differences between montane and lowland habitats in eastern North America may play a key role in the origin of new species.

DOES NICHE CONSERVATISM PROMOTE SPECIATION? A CASE STUDY IN NORTH AMERICAN SALAMANDERS

Recent speciation research has generally focused on how lineages that originate in allopatry evolve intrinsic reproductive isolation, or how ecological divergence promotes nonallopatric speciation. However, the ecological basis of allopatric isolation, which underlies the most common geographic mode of speciation, remains poorly understood and largely unstudied. Here, we explore the ecological and evolutionary factors that promote speciation in Desmognathus and Plethodon salamanders from temperate eastern North America. Based on published molecular phylogenetic estimates and the degree of geographic range overlap among extant species, we find strong evidence for a role for geographic isolation in speciation. We then examine the relationship between climatic variation and speciation in 16 sister-taxon pairs using geographic information system maps of climatic variables, new methods for modeling species' potential geographic distributions, and data on geographic patterns of genetic variation. In contrast to recent studies in tropical montane regions, we found no evidence for parapatric speciation along climatic gradients. Instead, many montane sister taxa in the Appalachian Highlands inhabit similar climatic niches and seemingly are allopatric because they are unable to tolerate the climatic conditions in the intervening lowlands. This temporal and spatial-ecological pattern suggests that niche conservatism, rather than niche divergence, plays the primary role in promoting allopatric speciation and montane endemism in this species-rich group of vertebrates. Our results demonstrate that even the relatively subtle climatic differences between montane and lowland habitats in eastern North America may play a key role in the origin of new species.

Mnioloma fuscum (Marchantiopsida: Calypogeiaceae), an unexpected addition to the indigenous flora of New Zealand

Mnioloma fuscum, a liverwort species known to date primarily from tropical-montane regions, is reported for New Zealand for the first time. Its occurrence in New Zealand is unexpected as the next nearest known site is believed to be the Solomon Islands, some 3500 km distant. The occurrence of Mnioloma fuscum in New Zealand highlights the contribution tropical regions have made to the composition of New Zealand's hepatic flora.

Watershed Management in the Pacific Slope Buffer Zone of the La Amistad Biosphere Reserve, Costa Rica

An analysis of watershed management in the Pacific slope of the Cordillera de Talamanca, Costa Rica, was conducted as part of a larger analysis of Conservation International's Amistad Conservation and Development (AMISCONDE) Initiative. General impacts of land use conversion are described with particular reference to tropical montane regions under conditions like those found on the Pacific slope of the Talamanca range. The quality of watershed management across the region and within the San Jerónimo-Zapotal watershed, one of the AMISCONDE Initiative sites, is evaluated. Significant problems are indicated regarding soil erosion, sedimentation, and agrochemical delivery to streams. These problems are likely due in part to the clearing of forest for cultivation on steep, highly erodable lands with little control over the location and construction of fields and associated infrastructure; a shift in land use from pasture to coffee cultivation and attendant increases in pesticide use; and unsafe pesticide application procedures. A lack of coordination among regulatory agencies, a nationwide lack of information regarding indicators of watershed health, and a lack of prioritization of restoration efforts within the AMISCONDE Initiative are possible factors contributing to the persistence of these problems. The authors advocate increased coordination among government agencies; the creation of central institutions for gathering and disseminating information regarding water quality, pesticide use, and pesticide impacts; and the prioritization of AMISCONDE restoration efforts within the San Jerónimo-Zapotal watershed to focus on riparian zones and other sensitive areas.

Recent diversification in African greenbuls (Pycnonotidae:Andropadus) supports a montane speciation model

It is generally accepted that accentuated global climatic cycles since the Plio–Pleistocene (2.8 Ma ago) have caused the intermittent fragmentation of forest regions into isolated refugia thereby providing a mechanism for speciation of tropical forest biota contained within them. However, it has been assumed that this mechanism had its greatest effect in the species rich lowland regions. Contrary evidence from molecular studies of African and South American forest birds suggests that areas of recent intensive speciation, where mostly new lineages are clustered, occur in discrete tropical montane regions, while lowland regions contain mostly old species. Two predictions arise from this finding. First, a species phylogeny of an avian group, represented in both lowland and montane habitats, should be ordered such that montane forms are represented by the most derived characters. Second, montane speciation events should predominate within the past 2.8 Ma. In order to test this model I have investigated the evolutionary history of the recently radiated African greenbuls (genus Andropadus ), using a molecular approach. This analysis finds that montane species are a derived monophyletic group when compared to lowland species of the same genus and recent speciation events (within the Plio–Pleistocene) have exclusively occurred in montane regions. These data support the view that montane regions have acted as centres of speciation during recent climatic instability.

Pollination, Fecundity, and the Distribution of Moth-Flowered Plants

The upper altitudinal limits of moth-pollinated plants are correlated with temperatures that restrict the activity of their crepuscular pollinators. The activity of hawkmoths decreases with temperature below 15'C. The number of Calliandra flowers visited and pollinated and the amount of pollen on Oenothera stigmas decrease with elevation. Fruit set and fecundity of most Calliandra populations and fruit set of Yacca are also negatively correlated with elevation. We suggest that the upper altitudinal limits of hawkmoth-flowered plants in tropical montane regions are restricted by low temperatures which restrict the activity of their pollinators. Because the hawkmoth-flower interaction may be diurnal in temperate regions and tropical habitats without hummingbirds, we speculate that a shift in the interaction from a nocturnal to a diurnal rhythm in New World tropical montane regions is inhibited by competitive interactions with hummingbirds. FECUNDITY IN XENOGAMOUS (OUT-CROSSING) PLANTS iS, in part, a function of the interaction between their flowers and pollen vector (s). In some animal-pollinated plants, maximum fecundity occurs only if each flower is visited a number of times. In Oenothera fraticosa L. a minimum of three or four visits by honey bees is required to transfer enough pollen to achieve maximum fecundity (Primack and Silander, pers. comm.). Environmental factors that limit the activity of a plant's pollinator(s) decrease the plant's fecundity (Cruden 1972) because each flower receives less than the number of visits required to maximize fecundity. Three sets of observations suggest that low temperatures may influence the fecundity and thus limit the distribution of moth-flowered plants in montane regions. First, low temperatures resulted in poor pollination of Mirabilis nyctaginea (Michx.) MacMill. flowers (Cruden 1973). Second, field observations in Mexico indicated that hawkmoth-flowered plants, which are relatively common in lowand mid-elevation ecosystems, are absent or rare in high-elevation ecosystems. This observation was corroborated by a survey of specimens of hawkmoth-flowered species in five genera (fig. 1). Finally, various species of Yucca in the western United States reach their upper elevational limits at 2600 m (Harrington 1964, McCleary and Wagner 1973), and in California most Yucca populations occur below 2000 m, with a few found up to 2450 m (Munz 1965). These observations suggest a testable hypothesis. Because temperatures decrease with increased elevation and moth activity decreases with decreased temperature (Harling 1968), moth activity should decrease with elevation resulting in a negative relationship between plant fecundity and elevation. We present data on pollination success, fruit set, and fecundity in moth-flowered species of Calliandra (Leguminosae: Mimosoideae), Oenothera (Onagraceae), and Yicca (Agavaceae) that support the above hypothesis and discuss the distribution of moth-flowered plants with respect to pollinator acti-