Five palaeobiological laws needed to understand the evolution of the living biota.

Dictated by limited resource availability for land acquisition, a central question in conservation biology is the ability of areas of different size to maintain species diversity. The selected reserves should not only be species rich at the moment, but should also maintain species diversity in the long run. We used two sets of data on vascular plant species in boreal lakes collected in 1933/34 and 1996 to test the relationships between lake area and the extinction, immigration and turnover rates of the species. Moreover, we investigated, whether the number of species in 1933/34 or water connection between lakes was related to extinction, immigration and turnover rates of species. We found that lake area or shoreline length was not correlated with immigration or turnover rate. But extinction rate was slightly negatively correlated with shoreline length. The original number of species was positively related to the number of species extinctions and to the absolute turnover rate in the lakes, which indicates that species richness does not create stability in these communities. Species number was not correlated with immigration rate. Upstream water connections in the lakes did not affect immigration, extinction or turnover rates. We conclude that length of the shoreline is a better measure of suitable area for water plants than the lake area, and that because the correlation between shoreline length and extinction rate was slight, also small lakes can be valuable for conservation.

Relationships between local annual immigration and extinction rates of plant species and total species richness were determined from long-term data in permanent plots in tallgrass and shortgrass prairies in Kansas. Combining plots resulted in higher equilibrium numbers of species as predicted from immigration and extinction rates. Immigration and extinction rates also increased with scale. Extinction rates are higher because the regional scale supports more rare species which, in turn, have high probabilities of extinction. We also tested the hypotheses that extinction rates would be higher on burned versus unburned grasslands, and that immigration rates would be higher on grazed versus ungrazed grasslands. Extinction rates were positively correlated with the number of species at a site, and this relationship was not altered by burning or grazing. Immigration rates were variable, but were sometimes positively correlated with growing season precipitation. Immigration rates decreased in years sites were burned. Therefore, after fire, the number of species going locally extinct was still dependent on earlier species richness, but the number of species added to the site was reduced. Variances in immigration and extinction rates were high, therefore, confident predictions regarding the effects of burning or grazing regimes on species richness could not be made. Variance in rates of immigration and extinction results in a range of values within which the equlibrium number of species fluctuates randomly.

We critically examine Wilcox's recent study which purports to prove dynamic equilibrium theory by demonstrating a species diversity-age relationship for lizard faunas on seventeen Baja California 'supersaturated' islands. We show both conceptual and technical problems with his analysis and propose an alternative explanation for his results. The proposition that species diversity results from balanced rates of species immigrations and extinctions was popularized by Preston (1962) and MacArthur & Wilson (1963, 1967). The experiments of Simberloff & Wilson (1970) and subsequently many others (see references in Simberloff, 1974) have been construed as conclusive support of this hypothesis. For several years, the hypothesis received little criticism. This 'dynamic equilibrium theory' states that species number remains constant because of observable but balanced species extinctions and immigrations, while species composition constantly changes. The existence of immigration, extinction, and 'turnover' (changes in species composition in the absence of changes in species number) is crucial to this theory. Lynch & Johnson (1974) criticized Diamond's (1969) conclusion that species 'turnover' is significant. Subsequently, Smith (1975) suggested that the high apparent rate of turnover was a problem of scale, and that as 'extinction' and 'immigration' has been defined, the equilibrium hypothesis was trivial. Simberloff (1976) recalculated his estimates of turnover for mangrove island arthropods and concluded that although turnover consisting of population extinctions occurred, far more of the original estimates represented either transient intra-population movement or death of individuals which never produced populations in the first place. Thus, the very experiments cited as the foundation for the dynamic equilibrium hypothesis were found not to evidence much turnover. Recently, Wilcox (1978) has contended that if 'non-equilibrium, supersaturated' island faunas are 'relaxing' (decreasing in species numbers), this can be construed as support for dynamic equilibrium theory. Were he to demonstrate such a relationship, it could be taken as support for Diamond's (1972) and Terborgh's (1975) ideas of long relaxation times. However, it has no bearing on dynamic equilibrium theory, since, as mentioned above, the critical requirement for dynamic equilibrium is observable, balanced rates of species immigrations and extinctions with species composition changes in the absence of changes in species number. Not only are Wilcox's (1978) conclusions irrelevant to the controversy involving dynamic equilibrium theory, but his analysis of the island agediversity relationship for lizard faunas on the islands in the Baja California region is beset with conceptual and technical problems that undermine its implication of long relaxation times. Given the omnipresent species-area relationship (Connor & McCoy, 1979) one would expect changes in island area resulting from sea level fluctuations to affect island 0305-0270/79/1200-0311 $02.00 ? 1979 Blackwell Scientific Publications 311 20 This content downloaded from 207.46.13.134 on Sun, 25 Sep 2016 05:00:36 UTC All use subject to http://about.jstor.org/terms 312 Stanley H. Faeth and Edward F. Connor species numbers. Diamond (1972), Terborgh (1975), Simpson (1974), and now Wilcox (1978) suggest that changes in species numbers resulting from such events do not occur instantaneously, but lag several thousand years behind changes in an island's physiographic characteristics, particularly area. Relaxation curves showing this trajectory of species loss over time (Terborgh, 1975) are usually a virtual mirror image of the familiar colonization curve (MacArthur & Wilson, 1963; Simberloff & Wilson, 1970). However, relaxation times are said to be extremely protracted, unlike those for colonization. Relaxing islands are thus supersaturated with species and are losing species in an inexorable return to the 'proper' number of species for a given island's area, and in Wilcox's example (1978), latitude. Wilcox presumes the islands in the Baja California region to be supersaturated, since when the islands were connected to the mainland the resident numbers of lizard species would have been some larger subset of the large mainland pool. Now isolated, the islands presumably retain more species than they 'should' have for their size and latitude. Specifically, Wilcox relates lizard species diversity to island age on seventeen Baja California land bridge islands, as well as to island area, elevation, isolation, distance from mainland, and latitude. He reasons that the observation of an inverse relationship between island age and diversity implies that young islands are still supersaturated and relaxing. He explores this relationship in three ways: (1) simple correlation between island area and diversity, (2) stepwise multiple regression techniques using species diversity as the dependent variable with island age and other physical parameters as explanatory variables, and (3) a type of partial correlation analysis where, after the effects of area and latitude are 'factored out,' residual species diversity is plotted against age. He then construes the plot of residual species diversity versus age as proof that species diversity is 'relaxing' toward an equilibrium value consistent with the present size and latitude of the island.

As humans alter habitats worldwide, developing reliable methods of assessing biodiversity and community attributes of interest (e.g., species richness, turnover, and extinction rates) is important. Frequently, estimates of community‐level attributes are biased because the estimators make assumptions of the data that are violated; many published studies assume equal detectability across species, sites, or time. The accuracy of estimators of species richness and community‐level vital rates (e.g., extinction and colonization) can be increased by using probabilistic estimation methods, which do not assume that all species are detected, or that the data assume a particular statistical distribution.Using these estimation methods, we examined avian community dynamics in a fragmented tropical landscape using data from five years of a mark–release–recapture study. For the resident understory avifauna in each of five small (∼0.3–20 ha), isolated forest fragments in southern Costa Rica, we estimated species richness, rate of change in species richness, extinction and turnover rates of species, and the number of colonizing species over temporal scales of one month, one year, and two years. We expected that community dynamics would be higher in smaller fragments than in larger fragments, reflecting greater temporal variability of avian communities in relatively small habitat patches. Additionally, a selective logging operation was conducted at one of our sites during the midpoint of this study, which gave us the opportunity to examine how community‐level vital rates may reflect the effects of that perturbation.Our results demonstrate that avian communities in the larger fragments were more stable than those in the smaller fragments, and that the selectively logged fragment was the most unstable of all. We found that extinction rates were more similar across our sites than were colonization rates, and that the higher instability of the small fragments was due primarily to higher levels of colonization. Although our sample size (n = 5) precludes strong inference, our findings are consistent with the prediction of higher local dynamics within small fragments and after logging. Taken together, these findings suggest that smaller fragments are more dynamic over time, and that ecological processes and multitrophic relationships at these dynamic sites may be in a constant state of flux.

We discuss the patterns of introduction and extinction of the species of land birds (passeriforms and columbiforms) introduced to the Hawaiian Islands over the last century. The data are consistent with the idea that rising extinction rates will eventually match immigration rates leading to a dynamic equilibrium. Turnover in species composition is a prominent feature of the introduced Hawaiian avifauna with extinctions common even among populations that had persisted for decades. We could not detect an effect of island size on extinction rate. However, the per species extinction rates do increase with the number of species on the island. This suggests that the species mutually affect each other's chances of extinction. Other explanations for an increasing per-species extinction rate do not seem to be consistent with our data. Thus, interspecific competition seems to have been an important process in determining extinction rate and, by extension, the equilibrium number of species on these islands.

Habitat fragmentation is one of the most important threats to biodiversity. Decreasing patch size may lead to a reduction in the size of populations and to an increased extinction risk of remnant populations. Furthermore, colonization rates may be reduced in isolated patches. To investigate the effects of isolation and patch size on extinction and colonization rates of plant species, calcareous grasslands at three sites in the Swiss Jura Mountains were experimentally fragmented into patches of 0.25, 2.25, and 20.25 m2 by frequent mowing of the surrounding area from 1993 to 1999. Species richness in the fragment plots and adjacent control plots of the same sizes was recorded during these 7 years. In agreement with the theory of island biogeography, colonization rate was reduced by 30% in fragments versus non-isolated controls, and extinction increased in small versus large plots. Habitat specialists, in contrast to generalists, were less likely to invade fragments. In the last 4 years of the experiment, extinction rates tended to be higher in fragment than in control plots at two of the three sites. Despite reduced colonization rates and a tendency of increased extinction rates in fragments, fragmented plots had only marginally fewer species than control plots after 7 years. Hence, rates were a more sensitive measure for community change than changes in species richness per se. From a conservation point of view, the detected reduced colonization rates are particularly problematic in small fragments, which are more likely to suffer from high extinction rates in the long run.

Plant-diversity hotspots on a global scale are well established, but smaller local hotspots within these must be identified for effective conservation of plants at the global and local scales. We used the distributions of endemic and endemic-threatened species of Myrtaceae to indicate areas of plant diversity and conservation importance within the Atlantic coastal forests (Mata Atlântica) of Brazil. We applied 3 simple, inexpensive geographic information system (GIS) techniques to a herbarium specimen database: predictive species-distribution modeling (Maxent); complementarity analysis (DIVA-GIS); and mapping of herbarium specimen collection locations. We also considered collecting intensity, which is an inherent limitation of use of natural history records for biodiversity studies. Two separate areas of endemism were evident: the Serra do Mar mountain range from Paraná to Rio de Janeiro and the coastal forests of northern Espírito Santo and southern Bahia. We identified 12 areas of approximately 35 km(2) each as priority areas for conservation. These areas had the highest species richness and were highly threatened by urban and agricultural expansion. Observed species occurrences, species occurrences predicted from the model, and results of our complementarity analysis were congruent in identifying those areas with the most endemic species. These areas were then prioritized for conservation importance by comparing ecological data for each.

Are polyploids really evolutionary dead-ends (again)? A critical reappraisal of Mayrose etal. ().

AimBiodiversity hotspots are regions with the highest species richness, and the most threatened species. Previous studies have shown that the extinction risk may be more related to evolutionary history than to species' traits. However, there is a knowledge gap on the relationship between evolutionary history and species extinction risk in biodiversity hotspots. Here, we link evolutionary history to species extinction risk for flowering plants (angiosperms) in global biodiversity hotspots.LocationGlobal biodiversity hotspots.MethodsWe calculated historical evolutionary measures (family species richness, family age, family diversification rate and the ratio of crown age to stem age) of angiosperms from 36 global biodiversity hotspots, which were grouped into 27 regions. Bayesian binomial‐logit univariate and multivariable regression models in conjunction with phylogenetic control and null models were used to identify the evolutionary history predictors of extinction risk for the 27 regions as a whole and for each of the regions.ResultsFamily species richness, family age and family diversification rate are all good indicators for predicting extinction risk. Specifically, when all the 27 regions were considered as a whole, families with higher species richness, older age and/or faster diversification rates have a higher risk of species extinction. However, high extinction risk in some regions, especially in temperate regions, tends to occur in families with low species richness and low diversification rates.Main conclusionsGeographic origin and evolutionary history of species should be jointly taken into account in conservation planning. In general, protection priority should be given to families with high species richness, ancient origins and fast diversification rate because these families seem to be prone to higher extinction risk. Additionally, different strategies should be applied to protect biodiversity in temperate versus tropical regions given that factors affecting extinction risk are different between these regions.

According to when they attained high diversity, major taxa of marine animals have been clustered into three groups, the Cambrian, Paleozoic, and Modern Faunas. Because the Cambrian Fauna was a relatively minor component of the total fauna after mid-Ordovician time, the Phanerozoic history of marine animal diversity is largely a matter of the fates of the Paleozoic and Modern Faunas. The fact that most late Cenozoic genera belong to taxa that have been radiating for tens of millions of years indicates that the post-Paleozoic increase in diversity indicated by fossil data is real, rather than an artifact of improvement of the fossil record toward the present.Assuming that ecological crowding produced the so-called Paleozoic plateau for family diversity, various workers have used the logistic equation of ecology to model marine animal diversification as damped exponential increase. Several lines of evidence indicate that this procedure is inappropriate. A plot of the diversity of marine animal genera through time provides better resolution than the plot for families and has a more jagged appearance. Generic diversity generally increased rapidly during the Paleozoic, except when set back by pulses of mass extinction. In fact, an analysis of the history of the Paleozoic Fauna during the Paleozoic Era reveals no general correlation between rate of increase for this fauna and total marine animal diversity. Furthermore, realistically scaled logistic simulations do not mimic the empirical pattern. In addition, it is difficult to imagine how some fixed limit for diversity could have persisted throughout the Paleozoic Era, when the ecological structure of the marine ecosystem was constantly changing. More fundamentally, the basic idea that competition can set a limit for marine animal diversity is incompatible with basic tenets of marine ecology: predation, disturbance, and vagaries of recruitment determine local population sizes for most marine species. Sparseness of predators probably played a larger role than weak competition in elevating rates of diversification during the initial (Ordovician) radiation of marine animals and during recoveries from mass extinctions. A plot of diversification against total diversity for these intervals yields a band of points above the one representing background intervals, and yet this band also displays no significant trend (if the two earliest intervals of the initial Ordovician are excluded as times of exceptional evolutionary innovation). Thus, a distinctive structure characterized the marine ecosystem during intervals of evolutionary radiation—one in which rates of diversification were exceptionally high and yet increases in diversity did not depress rates of diversification.Particular marine taxa exhibit background rates of origination and extinction that rank similarly when compared with those of other taxa. Rates are correlated in this way because certain heritable traits influence probability of speciation and probability of extinction in similar ways. Background rates of origination and extinction were depressed during the late Paleozoic ice age for all major marine invertebrate taxa, but remained correlated. Also, taxa with relatively high background rates of extinction experienced exceptionally heavy losses during biotic crises because background rates of extinction were intensified in a multiplicative manner; decimation of a large group of taxa of this kind in the two Permian mass extinctions established their collective identity as the Paleozoic Fauna.Characteristic rates of origination and extinction for major taxa persisted from Paleozoic into post-Paleozoic time. Because of the causal linkage between rates of origination and extinction, pulses of extinction tended to drag down overall rates of origination as well as overall rates of extinction by preferentially eliminating higher taxa having relatively high background rates of extinction. This extinction/origination ratchet depressed turnover rates for the residual Paleozoic Fauna during the Mesozoic Era. A decline of this fauna's extinction rate to approximately that of the Modern Fauna accounts for the nearly equal fractional losses experienced by the two faunas in the terminal Cretaceous mass extinction.Viewed arithmetically, the fossil record indicates slow diversification for the Modern Fauna during Paleozoic time, followed by much more rapid expansion during Mesozoic and Cenozoic time. When viewed more appropriately as depicting geometric—or exponential—increase, however, the empirical pattern exhibits no fundamental secular change: the background rate of increase for the Modern Fauna—the fauna that dominated post-Paleozoic marine diversity—simply persisted, reflecting the intrinsic origination and extinction rates of constituent taxa. Persistence of this overall background rate supports other evidence that the empirical record of diversification for marine animal life since Paleozoic time represents actual exponential increase. This enduring rate makes it unnecessary to invoke environmental change to explain the post-Paleozoic increase of marine diversity.Because of the resilience of intrinsic rates, an empirically based simulation that entails intervals of exponential increase for the Paleozoic and Modern Faunas, punctuated by mass extinctions, yields a pattern that is remarkably similar to the empirical pattern. It follows that marine animal genera and species will continue to diversify exponentially long into the future, barring disruption of the marine ecosystem by human-induced or natural environmental changes.

The origin and patterns of species diversity are fundamental themes in ecology and evolutionary biology. Insular systems play an important role in biogeography, and the species richness within an insular system has classically been considered as determined by the balance between the rate of speciation plus net migration and the rate of species extinction. A recent wave of studies integrating comprehensive phenotypic, phylogenetic, and environmental data is accumulating additional macroevolutionary insights at unprecedented scales. In this review, I summarize and discuss the hypothesis that intermediate dispersal ability leads to clades with high species diversity by recurrent speciation events (referred to as the intermediate dispersal hypothesis, IDH). Although some recent empirical and theoretical studies have supported the IDH, further integration of other ecological and evolutionary concepts spanning different timescales is needed to resolve long‐standing debates about the non‐linear relationship between diversification and organismal dispersal ability. This paper presents a framework for future studies that intend to test the IDH; I organize the factors that should be taken into account, including the indices for quantifying dispersal ability and species diversification, and methods of taxon sampling. The IDH requires more attention and could be used to unveil the diversity of extant species and how dispersal ability affects rates of speciation and extinction.

The Main Karoo Basin of South Africa contains a near-continuous sequence of continental deposition spanning ~80 Myr from the mid-Permian to the Early Jurassic. The terrestrial vertebrates of this sequence provide a high-resolution stratigraphic record of regional origination and extinction, especially for the mid–late Permian. Until now, data have only been surveyed at coarse stratigraphic resolution using methods that are biased by nonuniform sampling rates, limiting our understanding of the dynamics of diversification through this important time period. Here, we apply robust methods (gap-filler and modified gap-filler rates) for the inference of patterns of species richness, origination rates, and extinction rates to a subset of 1321 reliably-identified fossil occurrences resolved to approximately 50 m stratigraphic intervals. This data set provides an approximate time resolution of 0.3–0.6 Myr and shows that extinction rates increased considerably in the upper 100 m of the mid-Permian Abrahamskraal Formation, corresponding to the latest part of theTapinocephalusAssemblage Zone (AZ). Origination rates were only weakly elevated in the same interval and were not sufficient to compensate for these extinctions. Subsampled species richness estimates for the lower part of the overlying Teekloof Formation (corresponding to thePristerognathusandTropidostomaAZs) are low, showing that species richness remained low for at least 1.5–3 million years after the main extinction pulse. A high unevenness of the taxon abundance–frequency distribution, which is classically associated with trophically unstable postextinction faunas, in fact developed shortly before the acme of elevated extinction rates due to the appearance and proliferation of the dicynodontDiictodon. Our findings provide strong support for a Capitanian (“end-Guadalupian”) extinction event among terrestrial vertebrates and suggest that further high-resolution quantitative studies may help resolve the lack of consensus among paleobiologists regarding this event.

Changes in the species richness of (meta-)communities emerge from changes in the relative species abundance distribution (SAD), the total density of individuals, and the amount of spatial aggregation of individuals from the same species. Yet, how human disturbance affects these underlying diversity components at different spatial scales and how this interacts with important species traits, like dispersal capacity, remain poorly understood. Using data of carabid beetle communities along a highly replicated urbanization gradient, we reveal that species richness in urban sites was reduced due to a decline in individual density as well as changes in the SAD at both small and large spatial scales. Changes in these components of species richness were linked to differential responses of groups of species that differ in dispersal capacity. The individual density effect on species richness was due to a drastic 90% reduction of low-dispersal individuals in more urban sites. Conversely, the decrease in species richness due to changes in the SAD at large (i.e., loss of species from the regional pool) and small (i.e., decreased evenness) spatial scales were driven by species with intermediate and high dispersal ability, respectively. These patterns coincide with the expected responses of these dispersal-type assemblages toward human disturbance, namely, (i) loss of low-dispersal species by local extinction processes, (ii) loss of higher-dispersal species from the regional species pool due to decreased habitat diversity, and (iii) dominance of a few highly dispersive species resulting in a decreased evenness. Our results demonstrate that dispersal capacity plays an essential role in determining scale-dependent changes in species richness patterns. Incorporating this information improves our mechanistic insight into how environmental change affects species diversity at different spatial scales, allowing us to better forecast how human disturbance will drive local and regional changes in biodiversity patterns.

AimMacArthur and Wilson's theory of island biogeography was revolutionary, and also inspired the more recent unified neutral theory of biodiversity and biogeography. The unified neutral theory has the potential to make predictions about island biogeography that are not well studied. Here we aim to unify the two theories by using an ecological neutral model to study immigration and extinction rates on islands – the cornerstone of MacArthur and Wilson's theory.MethodsWe conduct simulations of a spatially implicit neutral model and measure species abundances, immigration rates and extinction rates. We study the behaviour of the model at dynamic equilibrium and on approach to dynamic equilibrium both from volcanic origin (low initial diversity) and from land bridge origin (high initial diversity). We extend the model to study the effects of clustered immigration and to explicitly account for the distinction between immigration and colonization.ResultsOur model, in accord with the simplest version of MacArthur and Wilson's theory, predicts linear immigration and extinction rates as functions of species richness at dynamic equilibrium. In contrast, the approach to dynamic equilibrium produces rich and unexpected behaviour where immigration and extinction rates are non‐monotonic functions of species richness, at odds with other theory. Once examined, however, this behaviour makes biological sense and results from the influence of the species abundance distribution over immigration and extinction rates. The turnover predicted by our first model appears high, but can be lowered to realistic levels with an alternative model of clustered immigration or by accounting for the difference between the immigration of a new species and its true colonization of the island.Main conclusionsMacArthur and Wilson's theory of island biogeography and ecological neutral theory are different, but there are strong similarities in their assumptions and predictions that should not be overlooked when evaluating them. Our results highlight the importance of species abundances as indicators of immigration and extinction rates; species richness alone is insufficient. In particular, extinction rate and species abundances are unavoidably linked, as rarity usually precedes extinction.

Traditionally, community ecologists assumed that spe-cies differ in some aspects of their traits or responsesto the environment (i.e. their niches), which allow themto coexist in the same habitat (Hutchinson 1957, 1959).Recently, Hubbell (2001) and others (e.g. Bell 2001,2003) have suggested that this view is inadequate toexplain the diversity often observed in speciose systems.For example, hundreds to thousands of tree species livein tropical forests, which only have a handful of limitingresources such as water, light, and a variety of macro- andmicronutrients. Such high diversity, with so few resources,they argue, cannot be explained by niche theory.As an alternative to the traditional niche theory,Hubbell (2001) developed a neutral theory of commu-nity structure (see also Caswell 1976; Hubbell 1979;Hubbell & Foster 1986; Bell 2000, 2001, 2003; Chave L Chave 2004). In the neutral theory, pat-terns of species diversity, relative abundance, andcomposition are primarily a function of the size of themetacommunity, the dispersal rate of organisms withinthe metacommunity, and the rates of generation (spe-ciation) of new species (Bell 2001; Hubbell 2001; Chave2004). Because species are assumed to be identicalecologically, Hubbell termed his a ‘neutral theory’, bydirect analogy to neutral genes in population genetics.Hubbell further termed his theory ‘unified’ in that it issimultaneously able to predict diversity and relativeabundance of organisms in a locality, as well as bioge-ographic patterns of species composition.In this essay, I overview the key assumptions (inputs)required and the insights (outputs) that can be gainedfrom each framework. While a complete discussion ofall of the assumptions and predictions of these modelsis beyond the scope of this essay (but see Chase