Non-linearities, synergisms and plant extinctions in South African fynbos and Australian kwongan

This paper explores the determinants of extinction of endemic plant taxa in mediterranean-climate regions in South Africa and southwestern Australia. Major threats to biodiversity in these areas include agriculture, deforestation, fragmentation, invasive alien organisms and urbanization. Case studies from the two regions show that synergisms between factors can lead to discontinuous, or non-linear, responses that have increased extinction rates (or threaten to) beyond predictions based on simple deterministic processes.     

Two key challenges for biodiversity: discontinuities and synergisms

The survival outlook for biodiversity is being profoundly and adversely influenced by the twin phenomena of discontinuities and synergisms. So potent are their impacts that they may well cause the mass extinction to overtake us more swiftly and extensively than is often expected. Despite their importance, however, we know all too little about these phenomena. They remain almost entirely a black hole of research. This paper, being an introduction to the special issue, presents a short selection of both phenomena, with an evaluation of their impacts on biodiversity. It concludes with an overview of the human enterprise and its probable future repercussions for biodiversity.     

How to resolve the SLOSS debate: Lessons from species-diversity models

The SLOSS debate - whether a single large reserve will conserve more species than several small - of the 1970s and 1980s never came to a resolution. The first rule of reserve design states that one large reserve will conserve the most species, a rule which has been heavily contested. Empirical data seem to undermine the reliance on general rules, indicating that the best strategy varies from case to case. Modeling has also been deployed in this debate. We may divide the modeling approaches to the SLOSS enigma into dynamic and static approaches. Dynamic approaches, covered by the fields of island equilibrium theory of island biogeography and metapopulation theory, look at immigration, emigration, and extinction. Static approaches, such as the one in this paper, illustrate how several factors affect the number of reserves that will save the most species.This article approaches the effect of different factors by the application of species-diversity models. These models combine species-area curves for two or more reserves, correcting for the species overlap between them. Such models generate several predictions on how different factors affect the optimal number of reserves. The main predictions are: Fewer and larger reserves are favored by increased species overlap between reserves, by faster growth in number of species with reserve area increase, by higher minimum-area requirements, by spatial aggregation and by uneven species abundances. The effect of increased distance between smaller reserves depends on the two counteracting factors: decreased species density caused by isolation (which enhances minimum-area effect) and decreased overlap between isolates. The first decreases the optimal number of reserves; the second increases the optimal number. The effect of total reserve-system area depends both on the shape of the species-area curve and on whether overlap between reserves changes with scale.The approach to modeling presented here has several implications for conservational strategies. It illustrates well how the SLOSS enigma can be reduced to a question of the shape of the species-area curve that is expected or generated from reserves of different sizes and a question of overlap between isolates (or reserves).     

Lessons from a great developmental biologist

The announcement that Sir John Gurdon had been awarded the 2012 Nobel Prize for Medicine or Physiology was received with great joy by developmental biologists. It was a very special occasion because of his total dedication to science and turning the Golden Rule of western civilization – love your neighbor as yourself – into a reality in our field. This essay attempts to explain how John became such a great scientific benefactor, and to review some of his discoveries that are less well known than the nuclear transplantation experiments. A few personal anecdotes are also included to illustrate the profound goodness of this unique man of science.     

Population genetic structure of two rare tree species (Colubrina oppositifolia and Alphitonia ponderosa,Rhamnaceae) from Hawaiian dry and mesic forests using random amplified polymorphic DNA markers

Hawaiian dry and mesic forests contain an increasingly rare assemblage of species due to habitat destruction, invasive alien weeds and exotic pests. Two rare Rhamnaceae species in these ecosystems, Colubrina oppositifolia and Alphitonia ponderosa, were examined using random amplified polymorphic DNA (RAPD) markers to determine the genetic structure of the populations and the amount of variation relative to other native Hawaiian species. Relative variation is lower than with other Hawaiian species, although this is probably not a consequence of genetic bottleneck. Larger populations of both species contain the highest levels of genetic diversity and smaller populations generally the least as determined by number of polymorphic loci, estimated heterozygosity, and Shannon's index of genetic diversity. Populations on separate islands were readily discernible for both species as were two populations of C. oppositifolia on Hawai'i island (North and South Kona populations). Substructure among Kaua'i subpopulations of A. ponderosa that were ecologically separated was also evident. Although population diversity is thought to have remained at predisturbance levels, population size continues to decline as recruitment is either absent or does not keep pace with senescence of mature plants. Recovery efforts must focus on control of alien species if these and other endemic dry and mesic forest species are to persist.     

Landslides significantly alter land cover and the distribution of biomass: an example from the Ninole ridges of Hawai'i

In the Ninole ridges of Hawai'i we investigated how landslides influence ecosystem development and modify land cover and the distribution of biomass. We estimated above and below-ground biomass, and N and P concentration in leaves (Metrosideros polymorpha) and very fine roots (all species), for vegetation developing on landslides of three age classes (young, < 18 yr; intermediate, 42 yr; and old ca. 124 yr) and on undisturbed soils (ca. 430 yr). The undisturbed soils were derived from ash underlain by basalt. To quantify changes in land cover and the distribution of biomass we combined our estimates of biomass with estimates of the area covered by each vegetation class. The latter estimates were obtained from the analysis and classification of color-infrared aerial photographs. Average above- and below-ground biomass for the herbaceous vegetation (young landslides) was 10.4 and 3.2 t/ha, whereas for the ohia-non ash forest (intermediate and old landslides) was 37.5 and 5.2 t/ha, respectively. For the ohia-ash forest (undisturbed sites), average above and below-ground biomass was 354.6 and 9.5 t/ha, respectively. Average foliar N for the herbaceous and ohia-non ash forest ranged between 0.80–0.84%, whereas root P between 0.056–0.040%, respectively. For the ohia-ash forest, average foliar and root P was 0.918% and 0.036%, respectively. Based on changes in vegetation cover during the last 430 yr, we estimated rate of disturbance at 15% per century or equivalently that 53 t/ha biomass per century exited through the system. The removal of ash-derived soils by landslides significantly alters successional trajectories and by doing so may be transforming the Ninole ecosystems in irreversible ways.     

Population structure of island-associated dolphins: Evidence from photo-identification of common bottlenose dolphins (Tursiops truncatus) in the main Hawaiian Islands

Management agencies often use geopolitical boundaries as proxies for biological boundaries. In Hawaiian waters a single stock is recognized of common bottlenose dolphins, Tursiops truncatus , a species that is found both in open water and near-shore among the main Hawaiian Islands. To assess population structure, we photo-identified 336 distinctive individuals from the main Hawaiian Islands, from 2000 to 2006. Their generally shallow-water distribution, and numerous within-year and between-year resightings within island areas suggest that individuals are resident to the islands, rather than part of an offshore population moving through the area. Comparisons of identifications obtained from Kaua'i/Ni'ihau, O'ahu, the "4-island area," and the island of Hawai'i showed no evidence of movements among these island groups, although movements from Kaua'i to Ni'ihau and among the "4-islands" were documented. A Bayesian analysis examining the probability of missing movements among island groups, given our sample sizes for different areas, indicates that interisland movement rates are less than 1% per year with 95% probability. Our results suggest the existence of multiple demographically independent populations of island-associated common bottlenose dolphins around the main Hawaiian islands.     

Lessons from 1950

Second-trimester maternal serum screening is a noninvasive means of identifying pregnant women at an increased risk for various conditions including a fetus with open spina bifida, fetal Down syndrome, trisomy 18, multiple gestation, and adverse pregnancy outcome. Combinations of several different markers are available for screening. These include alpha-fetoprotein, human chorionic gonadotropin, and unconjugated estriol. In this review, we discuss the benefits and limitations of the screening tests and the suggested protocols for the care of patients.