Combined effects of seed and soil quality drive seedling performance of a late‐successional canopy tree in a tropical forest

Habitat loss and fragmentation affect the structure and functioning of forested ecosystems worldwide, yet we lack an understanding of how species respond to environmental changes. Here, we examined reproductive success and seedling performance of Poulsenia armata (Moraceae) in continuous and fragmented forests of Los Tuxtlas, southern Mexico. We further investigated how maternal habitat and soil conditions manifested in the seedling stage. We determined seed quality and seedling performance by combining isotopic analyses in seed quality with field observations of P. armata fruit production and a common‐‐garden experiment. Soil conditions in forest fragments negatively impacted P. armata reproductive success. Trees of P. armata in forest fragments were smaller in size and produced fewer fruits and smaller seeds with lower quality compared with trees from the continuous forest. The combined effects of maternal habitat and soil conditions determined seedling survival and growth of this tropical tree. Notably, seedlings had restricted plasticity for biomass allocation to roots, limiting the capacity of fragmented populations to compensate for the initial low N content in seeds. Trees in forest fragments at Los Tuxtlas produced offspring competitively inferior and potentially less resilient than counterparts in continuous forest, jeopardizing future persistence of this late‐successional tree species.     

Population Dynamics of the Andean Lizard Anolis heterodermus: Fast‐slow Demographic Strategies in Fragmented Scrubland Landscapes

Habitat fragmentation and loss affect population stability and demographic processes, increasing the extinction risk of species. We studied Anolis heterodermus populations inhabiting large and small Andean scrubland patches in three fragmented landscapes in the Sabana de Bogotá (Colombia) to determine the effect of habitat fragmentation and loss on population dynamics. We used the capture‐mark‐recapture method and multistate models to estimate vital rates for each population. We estimated growth population rate and the most important processes that affect λ by elasticity analysis of vital rates. We tested the effects of habitat fragmentation and loss on vital rates of lizard populations. All six isolated populations showed a positive or an equilibrium growth rate (λ = 1), and the most important demographic process affecting λ was the growth to first reproduction. Populations from landscapes with less scrubland natural cover showed higher stasis of young adults. Populations in highly fragmented landscapes showed highest juvenile survival and growth population rates. Independent of the landscape's habitat configuration and connectivity, populations from larger scrubland patches showed low adult survivorship, but high transition rates. Populations varied from a slow strategy with low growth and delayed maturation in smaller patches to a fast strategy with high growth and early maturation in large patches. This variation was congruent with the fast‐slow continuum hypothesis and has serious implications for Andean lizard conservation and management strategies. We suggest that more stable lizard populations will be maintained if different management strategies are adopted according to patch area and habitat structure.     

Habitat fragmentation and population features differently affect fruit predation,fecundity and offspring performance in a non‐specialist gypsum plant

• The effects of habitat fragmentation on plant populations are complex, as it might disrupt many ecological processes, including plant reproduction and plant–animal interactions. Gypsum specialist plants may be resilient to fragmentation due to their evolutionary history in fragmented landscapes, but the effects on non‐specialist plants occurring in gypsum are unknown.
• We conducted a study focusing on different aspects of the reproductive cycle of Astragalus incanus subsp. incanus, a plant facultatively linked to gypsum soils. We focused on plant fecundity and pre‐dispersal predation, obtained from field observations, and offspring performance, assessed in a common garden. Beyond fragment size and connectivity, we also considered habitat quality, population size and density and plant size as predictors.
• Fragment size and connectivity had no effect on plant fecundity, but jointly determined fruit predation, while fragment size was positively related to offspring growth. Population density, rather than population size, had a positive effect on predation but negatively affected plant fecundity and offspring performance. Habitat quality reduced both plant fecundity and predation incidence.
• In this non‐specialist species, habitat fragmentation, population features and habitat quality affect different facets of plant performance. Predation was the only process clearly affected by fragmentation variables, fecundity mainly depended on population features and offspring performance and was better explained by mother plant identity. Our results show the need to consider habitat and population features together with fragment size and connectivity in order to assess the effects of fragmentation. Importantly, these effects can involve different aspects of plant reproduction, including plant–animal interactions.

     

Demographic response of plant populations to habitat fragmentation and temporal environmental variability

Many plant species currently exist in fragmented populations of different sizes, while they also experience unpredictable climatic fluctuation over time. However, we still understand little about how plant demography responds to such spatial and temporal environmental variability. We studied population dynamics of an understory perennial herb Trillium camschatcense in the Tokachi plain of Hokkaido, Japan, where a significant effect of forest fragmentation on seedling recruitment was previously reported. Four populations across a range of fragment sizes were studied for 6 years, and the data were analyzed using matrix population models. Per capita fecundity (the number of recruits per plant) varied greatly among populations, but the variation in population growth rates (λ) was mainly driven by the variation in stasis and growth rates, suggesting that the general trend of reduced fecundity in fragmented populations may not be readily translated into subsequent dynamics. Temporal variation in λ among years was more than 2 times larger than spatial variation among populations, and this result was likely attributable to the contrasting response of correlation structures among demographic rates. The among-population variation in λ was dampened by negative covariation between matrix elements possibly due to density-dependent regulation as well as an inherent constraint that some elements are not independent, whereas positive covariation between matrix elements resulted in large temporal variation in λ. Our results show that population dynamics responded differently to habitat fragmentation and temporal variability of the environment, emphasizing the need to discriminate these spatial and temporal variations in demographic models. Although no populations were projected to be declining in stochastic simulations, correlation between current habitat size and plant density implies historical λ is positively related to habitat size.     

Habitat fragmentation influences genetic diversity and differentiation: Fine‐scale population structure of Cercis canadensis (eastern redbud)

Forest fragmentation may negatively affect plants through reduced genetic diversity and increased population structure due to habitat isolation, decreased population size, and disturbance of pollen‐seed dispersal mechanisms. However, in the case of tree species, effective pollen‐seed dispersal, mating system, and ecological dynamics may help the species overcome the negative effect of forest fragmentation. A fine‐scale population genetics study can shed light on the postfragmentation genetic diversity and structure of a species. Here, we present the genetic diversity and population structure of Cercis canadensis L. (eastern redbud) wild populations on a fine scale within fragmented areas centered around the borders of Georgia–Tennessee, USA. We hypothesized high genetic diversity among the collections of C. canadensis distributed across smaller geographical ranges. Fifteen microsatellite loci were used to genotype 172 individuals from 18 unmanaged and naturally occurring collection sites. Our results indicated presence of population structure, overall high genetic diversity (H_E = 0.63, H_O = 0.34), and moderate genetic differentiation (F_ST = 0.14) among the collection sites. Two major genetic clusters within the smaller geographical distribution were revealed by STRUCTURE. Our data suggest that native C. canadensis populations in the fragmented area around the Georgia–Tennessee border were able to maintain high levels of genetic diversity, despite the presence of considerable spatial genetic structure. As habitat isolation may negatively affect gene flow of outcrossing species across time, consequences of habitat fragmentation should be regularly monitored for this and other forest species. This study also has important implications for habitat management efforts and future breeding programs.     

Demography and dynamics of three wild horse populations in the Australian Alps

Wild horses (Equus caballus) are a non‐native species occupying over 2800 km² of the nationally significant Australian Alps National Parks. We estimated key demographic parameters (fecundity, adult and juvenile survival and annual finite population growth rate) over 3 years and related these to horse body condition and available food for three populations under natural conditions, and found a trend consistent with food limitation. The populations were independent, with different site characteristics and occupied areas, identified by land managers, as areas of concern about possible conservation impacts. Annual fecundity and juvenile survival varied across sites averaging between 0.21 and 0.31 female young per adult female, and 0.83 and 0.90 per annum, respectively, and annual adult survival was consistent across sites averaging 0.91 per annum. One population was increasing (λ = 1.09 year^?1; 95% CI 1.04–1.14) and two populations were stable (λ ～ 1.0 year^?1). Mean body condition of horses was positively correlated with mean pasture biomass rank. Across the three populations, fecundity, recruitment, body condition and annual finite population growth rate were lowest when mean pasture biomass rank was lowest and conversely highest when pasture rank was highest. We conclude that food limitation appears to be operating across these three sites. We used our results to assess the sensitivity of annual finite rate of increase (λ) to changes in key demographic parameters and found that λ was most sensitive to a change in adult survival, with the second most sensitive parameter being fecundity. Thus, if the aim of management is to reduce the size of the wild horse population then targeting adult survival is most important, followed by fecundity. Finally, we estimated the linear, negative, numerical response for wild horses between annual λ and horses per unit pasture biomass.     

Post‐fragmentation population structure in a cooperative breeding Afrotropical cloud forest bird: emergence of a source‐sink population network

The impact of demographic parameters on the genetic population structure and viability of organisms is a long‐standing issue in the study of fragmented populations. Demographic and genetic tools are now readily available to estimate census and effective population sizes and migration and gene flow rates with increasing precision. Here we analysed the demography and genetic population structure over a recent 15‐year time span in five remnant populations of Cabanis's greenbul (Phyllastrephus cabanisi), a cooperative breeding bird in a severely fragmented cloud forest habitat. Contrary to our expectation, genetic admixture and effective population sizes slightly increased, rather than decreased between our two sampling periods. In spite of small effective population sizes in tiny forest remnants, none of the populations showed evidence of a recent population bottleneck. Approximate Bayesian modelling, however, suggested that differentiation of the populations coincided at least partially with an episode of habitat fragmentation. The ratio of meta‐N_e to meta‐N_c was relatively low for birds, which is expected for cooperative breeding species, while N_e/N_c ratios strongly varied among local populations. While the overall trend of increasing population sizes and genetic admixture may suggest that Cabanis's greenbuls increasingly cope with fragmentation, the time period over which these trends were documented is rather short relative to the average longevity of tropical species. Furthermore, the critically low N_c in the small forest remnants keep the species prone to demographic and environmental stochasticity, and it remains open if, and to what extent, its cooperative breeding behaviour helps to buffer such effects.     

Demographic variation in cycad populations inhabiting contrasting forest fragments

Reduced habitat quality after fragmentation can significantly affect population viability, but the effects of differing quality of the remaining habitat on population fitness are rarely evaluated. Here, I compared fragmented populations of the cycad Zamia melanorrhachis from habitats with different history and subject to contrasting levels of disturbance to explore potential demographic differences in populations across habitat patches that could differ in habitat quality. Secondary-forest fragments had a lower canopy cover and soil moisture than remnant-forest fragments, which may represent a harsh environment for this cycad. A smaller average plant size and lower population density in the secondary-forest fragments support the hypothesis that these fragments may be of lower quality, e.g., if plants have reduced survival and/or fecundity in these habitats. However, variation in the stage-structure of populations (i.e., the relative proportions of non-reproductive and reproductive plants) was associated with the area of the forest fragments rather than the type of habitat (remnant versus secondary forest). These results suggest that different demographic parameters may respond differently to habitat fragmentation, which may be explained if processes like adult survival and recruitment depend on different characteristics of the habitat, e.g., average light/water availability versus suitable area for plant establishment. This study shows that forest fragments may differ drastically in environmental conditions and can sustain populations that can vary in their demography. Understanding how forest fragments may represent different habitat types is relevant for evaluating population viability in a heterogeneous landscape and for designing conservation programs that account for this heterogeneity.     

Effects of regional climate and small‐scale habitat quality on performance in the relict species Ramonda myconi

Abstract. The Mediterranean Basin harbours paleo‐endemic species with a highly restricted and fragmented distribution. Many of them might also be of the remnant type, for which the regional dynamics depends on the persistence of extant populations. Therefore, a key issue for the long‐term persistence of these species is to assess the variability and effects of ecological factors determining plant performance. We investigated the spatio‐temporal variability in plant traits and ecological factors of Ramonda myconi, a preglacial relict species with remnant dynamics, in 5 populations over 4–7 yr. Ecological factors contributing to fecundity showed a high degree of between‐year variability. Pre‐dispersal fruit predation had a minor influence on total reproductive output, and most of the variability was found among individuals within populations and years. Spatio‐temporal variability in growth and survival was rather low but significant, whereas recruitment showed important between‐population variability. Among‐year variability in fecundity and growth was related to climatic fluctuations on a regional scale, notably rainfall and temperature in a particular period, while the spatial variability in survival and recruitment was explained by within‐population (patch) habitat quality. Although R. myconi is able to withstand repeated periods of drought, water availability seems to be the most important factor affecting plant performance in all the study populations. These findings suggest that the long‐term persistence of species showing remnant population dynamics in habitats under the influence of Mediterranean climate might be threatened by increased aridity as a result of climate change.     

Population dynamics of Echinops gmelinii Turcz. at different successional stages of biological soil crusts in a temperate desert in China

• The effects of biological soil crusts (BSC) on vascular plant growth can be positive, neutral or negative, and little information is available on the impacts of different BSC successional stages on vascular plant population dynamics.
• We analysed seedling emergence, survival, plant growth and reproduction in response to different BSC successional stages (i.e. habitats: bare soil, cyanobacteria, lichen and moss crusts) in natural populations of Echinops gmelinii Turcz. in the Tengger Desert of northwest China. The winter annual E. gmelinii is a dominant pioneer herb after sand stabilisation.
• During the early stages of BSC succession, the studied populations of E. gmelinii were characterised by high density, plant growth and fecundity. As the BSC succession proceeded beyond moss crusts, the fecundity decreased sharply, which limited seedling recruitment. Differences in seedling survival among the successional stages were not evident, indicating that BSC have little effect on survival in arid desert regions. Moreover, E. gmelinii biomass allocation exhibited low plasticity, and only reproductive allocation was sensitive to the various habitats. Our results further suggest that the negative effects of BSC succession on population dynamics are primarily driven by increasing topsoil water‐holding capacity and decreasing rain water infiltration into deeper soil.
• We conclude that BSC succession drives population dynamics of E. gmelinii, primarily via its effect on soil moisture. The primary cause for E. gmelinii population decline during the moss‐dominated stage of BSC succession is decreased fecundity of individual plants, with declining seed mass possibly reducing the success of seedling establishment.

     

Offspring performance and recruitment of the pioneer tree Acacia caven (Fabaceae) in a fragmented subtropical dry forest

The process of habitat fragmentation results in the breaking apart of originally continuous habitats, causing multiple changes in biotic and abiotic interactions. Alterations in resource availability and in mutualistic and antagonistic plant–animal interactions may impact plant offspring quantity and quality. Currently, several old fragmented systems evidence a process of flora homogenization, where shade‐tolerant species are replaced by pioneer light‐demanding species. Notably, the relationship between quantity and quality parameters of plant offspring production and the successful recruitment of pioneer species in fragmented forests has been poorly explored. Here, we assess population size, sapling recruitment and offspring performance of one of the most widespread tree species of subtropical South America, the native pioneer Acacia caven (Fabaceae). Population size of adults and saplings increased from small to continuous forests, whereas the sapling recruitment per adult tree (sapling/adult ratio) showed no significant differences among forests of different size. Seedling performance was negatively related to forest area and population size, implying potential superior competitive ability of seedlings produced in smaller populations compared to larger ones. Our results show that A. caven is resilient to habitat fragmentation effects, which may be ascribed to a set of advantageous ecological traits such as outcrossing, massive flowering, generalist pollination, drought resistance, rapid growth and re‐sprouting. Thus, this pioneer tree benefits from the availability of vacant sites and resources released by declining plant populations of other species, eventually becoming the dominant species in fragmented habitats. Pioneer native plant species with ecological traits such as A. caven may represent the silent successful survivors and new colonizers of fragmented habitats, the ubiquitous landscapes of the future.     

Comparative demography of two giant caulescent rosettes (Espeletia timotensis and E. spicata) from the high tropical Andes

Using field data from previous studies we built matrix models for two populations of giant rosettes, Espeletia timotensis Cuatrec. and E. spicata Sch. Bip. Wedd., from the Andes Cordillera in Mérida, Venezuela. We analysed the models and calculated population growth rate (λ), sensitivities, elasticities and the sensitivity of the elasticities to changes in the vital rates. The analysis showed that the two species behave alike in general demographic terms. In both models, population growth rate is positive and sensitivities of λ to changes in vital rates decrease markedly in this order: plant establishment, progression of juvenile–adult, germination and survival. The relative contributions of vital rates to λ (elasticities) are very similar to those of other woody plant species: a higher contribution of survival and a very low contribution of fecundity. Transition from seedling to juvenile is most important and the younger established stages (juveniles and young adults) play a predominant demographic role in both populations. Seed banks and older adults are playing a relatively minor role in the dynamics of both populations. However, they may be important in relation to unpredictable, favourable or detrimental events. Perturbation analysis of elasticities showed that increasing the rate of plant establishment will decrease the relative importance of stasis. We conclude that both species are demographically very close, and similar to other long‐lived woody plant species. However, the two species differ in the role of the seed bank, which seems more important in the demography of E. spicata than in E. timotensis.     

Linking vital rates to invasiveness of a perennial herb

Invaders generally show better individual performance than non-invaders and, therefore, vital rates (survival, growth, fecundity) could potentially be used to predict species invasiveness outside their native range. Comparative studies have usually correlated vital rates with the invasiveness status of species, while few studies have investigated them in relation to population growth rate. Here, I examined the influence of five vital rates (plant establishment, survival, growth, flowering probability, seed production) and their variability (across geographic regions, habitat types, population sizes and population densities) on population growth rate (λ) using data from 37 populations of an invasive, iteroparous herb (Lupinus polyphyllus) in a part of its invaded range in Finland. Variation in vital rates was often related to habitat type and population density. The performance of the populations varied from declining to rapidly increasing independently of habitat type, population size or population density, but differed between regions. The population growth rate increased linearly with plant establishment, and with the survival and growth of vegetative individuals, while the survival of flowering individuals and annual seed production were not related to λ. The vital rates responsible for rapid population growth varied among populations. These findings highlight the importance of both regional and local conditions to plant population dynamics, demonstrating that individual vital rates do not necessarily correlate with λ. Therefore, to understand the role of individual vital rates in a species ability to invade, it is necessary to quantify their effect on population growth rate.     

Effects of landscape matrix on population connectivity of an arboreal mammal,Petaurus breviceps

Ongoing habitat loss and fragmentation is considered a threat to biodiversity as it can create small, isolated populations that are at increased risk of extinction. Tree‐dependent species are predicted to be highly sensitive to forest and woodland loss and fragmentation, but few studies have tested the influence of different types of landscape matrix on gene flow and population structure of arboreal species. Here, we examine the effects of landscape matrix on population structure of the sugar glider (Petaurus breviceps) in a fragmented landscape in southeastern South Australia. We collected 250 individuals across 12 native Eucalyptus forest remnants surrounded by cleared agricultural land or exotic Pinus radiata plantations and a large continuous eucalypt forest. Fifteen microsatellite loci were genotyped and analyzed to infer levels of population differentiation and dispersal. Genetic differentiation among most forest patches was evident. We found evidence for female philopatry and restricted dispersal distances for females relative to males, suggesting there is male‐biased dispersal. Among the environmental variables, spatial variables including geographic location, minimum distance to neighboring patch, and degree of isolation were the most important in explaining genetic variation. The permeability of a cleared agricultural matrix to dispersing gliders was significantly higher than that of a pine matrix, with the gliders dispersing shorter distances across the latter. Our results added to previous findings for other species of restricted dispersal and connectivity due to habitat fragmentation in the same region, providing valuable information for the development of strategies to improve the connectivity of populations in the future.     

Does long‐distance pollen dispersal preclude inbreeding in tropical trees? Fragmentation genetics of Dysoxylum malabaricum in an agro‐forest landscape

Tropical trees often display long‐distance pollen dispersal, even in highly fragmented landscapes. Understanding how patterns of spatial isolation influence pollen dispersal and interact with background patterns of fine‐scale spatial genetic structure (FSGS) is critical for evaluating the genetic consequences of habitat fragmentation. In the endangered tropical timber tree Dysoxylum malabaricum (Meliaceae), we apply eleven microsatellite markers with paternity and parentage analysis to directly estimate historic gene flow and contemporary pollen dispersal across a large area (216 km²) in a highly fragmented agro‐forest landscape. A comparison of genetic diversity and genetic structure in adult and juvenile life stages indicates an increase in differentiation and FSGS over time. Paternity analysis and parentage analysis demonstrate high genetic connectivity across the landscape by pollen dispersal. A comparison between mother trees in forest patches with low and high densities of adult trees shows that the frequency of short‐distance mating increases, as does average kinship among mates in low‐density stands. This indicates that there are potentially negative genetic consequences of low population density associated with forest fragmentation. Single isolated trees, in contrast, frequently receive heterogeneous pollen from distances exceeding 5 km. We discuss the processes leading to the observed patterns of pollen dispersal and the implications of this for conservation management of D. malabaricum and tropical trees more generally.     

Effects of forest fragmentation on the lekking behavior of White-throated Manakins in Central Amazonia

Forest fragmentation can affect various aspects of population dynamics, but few investigators have assessed possible effects on the behavior of a species. Loss of habitat may limit population recruitment and abundance, which may alter breeding dynamics in forest remnants. We examined the lekking behavior of White-throated Manakins (Corapipo gutturalis) in a fragmented landscape to determine if forest fragmentation affected the spatial distribution of display courts and male behavior at courts. We captured and observed males at 19 courts located in 11 primary forests of different sizes in forest habitats of the Biological Dynamics of Forest Fragments Project area, an experimentally fragmented landscape located in the central Brazilian Amazon, and estimated their spatial distribution as the distance to the nearest court in the landscape. We quantified habitat loss using the proportion of forest cover surrounding courts and their distances to forest edges. No courts were detected in 1-ha forest fragments, suggesting direct effects from habitat loss following fragmentation that affected connectivity and thus recruitment and persistence of courts in the smallest fragments. The spatial distribution of display courts in forests larger than 10 ha remained unaltered, compared to display courts in continuous forests, but adult males were less numerous on courts with a higher percentage of forest cover and they displayed less on courts closer to forest edges. The spatial distribution of courts also contributed to variation in male social behavior, with more juvenile males present and adult males displaying at lower rates at more isolated courts. Although White-throated Manakins are locally common, the observed behavioral changes in response to habitat loss may affect their population dynamics. Our results show the importance of assessing behavioral changes in conservation programs and, in particular, of including biologically relevant measures of habitat loss in addressing its possible effects on species persistence in fragmented landscapes.     

A preliminary population viability analysis of the critically endangered blue‐eyed black lemur (Eulemur flavifrons)

Population viability analysis is an important tool to assess the extinction risk in small populations of highly specialized primates. The blue‐eyed black lemur (Eulemur flavifrons) is critically endangered with a restricted range in the north‐western dry deciduous forest of Madagascar, where habitat fragmentation and loss of forest connectivity threaten its survival. We performed a population viability analysis (PVA) of this lemur in Ankarafa Forest in the Sahamalaza Peninsula National Park, north‐western Madagascar, to determine the demographic parameters most influential for population persistence and to assess extinction probabilities. We conducted PVA analyses using different demographic parameters which characterize the species including reproduction, lifespan and population size using the software VORTEX for six scenarios with 100 iterations and simulated over 100 years. The simulations suggested the first extinction within 13 years when the percentage of habitat destruction increased up to 12%. Severe habitat destruction such as fire and logging was the major cause which led to the risk of population extinction. Conservation strategies, in particular measures to reduce habitat destruction, are proposed to ensure the survival of this critically endangered lemur.     

Metapopulation dynamics in a changing climate: Increasing spatial synchrony in weather conditions drives metapopulation synchrony of a butterfly inhabiting a fragmented landscape

Habitat fragmentation and climate change are both prominent manifestations of global change, but there is little knowledge on the specific mechanisms of how climate change may modify the effects of habitat fragmentation, for example, by altering dynamics of spatially structured populations. The long‐term viability of metapopulations is dependent on independent dynamics of local populations, because it mitigates fluctuations in the size of the metapopulation as a whole. Metapopulation viability will be compromised if climate change increases spatial synchrony in weather conditions associated with population growth rates. We studied a recently reported increase in metapopulation synchrony of the Glanville fritillary butterfly (Melitaea cinxia) in the Finnish archipelago, to see if it could be explained by an increase in synchrony of weather conditions. For this, we used 23 years of butterfly survey data together with monthly weather records for the same period. We first examined the associations between population growth rates within different regions of the metapopulation and weather conditions during different life‐history stages of the butterfly. We then examined the association between the trends in the synchrony of the weather conditions and the synchrony of the butterfly metapopulation dynamics. We found that precipitation from spring to late summer are associated with the M. cinxia per capita growth rate, with early summer conditions being most important. We further found that the increase in metapopulation synchrony is paralleled by an increase in the synchrony of weather conditions. Alternative explanations for spatial synchrony, such as increased dispersal or trophic interactions with a specialist parasitoid, did not show paralleled trends and are not supported. The climate driven increase in M. cinxia metapopulation synchrony suggests that climate change can increase extinction risk of spatially structured populations living in fragmented landscapes by altering their dynamics.     

Population stage structure,survival and recruitment in the endangered East African forest herb <Emphasis Type="Italic">Saintpaulia</Emphasis>

Climatic seasonality, local habitat quality, and edge effects created by forest fragmentation due to human activity may affect the performance of endangered rain forest understory herbs. Viability and seasonal dynamics of the populations of the endangered Saintpaulia confusa, S. difficilis, and S. grotei were studied in a protected seasonal submontane forest in NE Tanzania by examining plant life-history traits, population stage structure, and the effects of habitat quality on plant performance. The population stage structures were of the dynamic type. There was a lower frequency of seedlings (57.9%) and higher frequency of juvenile (13.3%) and adult plants (28.8%) in S. confusa than in S. difficilis (74%, 10.7% and 15.3%, respectively). Seedling recruitment occurred from May to August with an average of 54, 103 and 38 emerged seedlings per 1 m² study plot (S. confusa, S. difficilis, and S. grotei, respectively). Presence of the seed bank was also an indication of the regeneration potential of the populations. Mortality was high during the dry and hot season from December to March. Survival was lowest in juvenile plants, higher in sterile adult plants and the highest in fertile adult plants. Because survival was the lowest on dry substrates under open canopy, our data suggest that forest fragmentation, by reducing shade and humidity, will increase mortality in Saintpaulia. Furthermore, since the mortality was highest in seedlings and juveniles, forest fragmentation is likely to impede the regeneration of the Saintpaulia populations.