Double jeopardy and global extinction risk in corals and reef fishes.

Coral reefs are critically important ecosystems that support the food security and livelihoods of hundreds of millions of people in maritime tropical countries, yet they are increasingly threatened by overfishing, coastal pollution, climate change, and other anthropogenic impacts, leading to concerns that some species may be threatened with local or even global extinction. The concept of double jeopardy proposes that the risk of species extinction is elevated if species that are endemic (small range) are also scarce (low local abundance). Traditionally, marine macroecology has been founded on patterns of species richness and presence-absence data, which provide no information on species abundances or on the prevalence of double jeopardy.

Is regional species diversity bounded or unbounded?

Two conflicting hypotheses have been proposed to explain large-scale species diversity patterns and dynamics. The unbounded hypothesis proposes that regional diversity depends only on time and diversification rate and increases without limit. The bounded hypothesis proposes that ecological constraints place upper limits on regional diversity and that diversity is usually close to its limit.

Disentangling the drivers of β diversity along latitudinal and elevational gradients.

Understanding spatial variation in biodiversity along environmental gradients is a central theme in ecology. Differences in species compositional turnover among sites (β diversity) occurring along gradients are often used to infer variation in the processes structuring communities. Here, we show that sampling alone predicts changes in β diversity caused simply by changes in the sizes of species pools.

Navigating the multiple meanings of β diversity: a roadmap for the practicing ecologist.

A recent increase in studies of β diversity has yielded a confusing array of concepts, measures and methods. Here, we provide a roadmap of the most widely used and ecologically relevant approaches for analysis through a series of mission statements. We distinguish two types of β diversity: directional turnover along a gradient vs.

Spatial niches and coexistence: testing theory with tarweeds.

Competitive coexistence in a spatially heterogeneous environment is traditionally attributed to niche differences, but several recent theories have proposed important additional roles for propagule limitation and chance (e.g., neutral theory, stochastic niche theory, spatial storage effect).

Niche conservatism as an emerging principle in ecology and conservation biology.

The diversity of life is ultimately generated by evolution, and much attention has focused on the rapid evolution of ecological traits. Yet, the tendency for many ecological traits to instead remain similar over time [niche conservatism (NC)] has many consequences for the fundamental patterns and processes studied in ecology and conservation biology. Here, we describe the mounting evidence for the importance of NC to major topics in ecology (e.

Phylogeny, niche conservatism and the latitudinal diversity gradient in mammals.

Biologists have long searched for mechanisms responsible for the increase in species richness with decreasing latitude. The strong correlation between species richness and climate is frequently interpreted as reflecting a causal link via processes linked to energy or evolutionary rates. Here, we investigate how the aggregation of clades, as dictated by phylogeny, can give rise to significant climate-richness gradients without gradients in diversification or environmental carrying capacity.

Toward a better understanding of the regional causes of local community richness.

Despite widespread acknowledgement that local ecological communities are profoundly shaped by regional-scale influences, including evolutionary and biogeographic processes, this perspective has yet to be widely incorporated into ecological research. Drawing on recent research, we propose four steps towards making regional influences a stronger part of research on the richness of local communities: (1) identifying the regional-scale causes of variation in species richness in the systems ecologists study; (2) testing for effects of regional richness on local richness, using improved observational and experimental analyses to overcome earlier problems; (3) simultaneously analysing environmental influences on regional and local species richness as well as the influence of regional richness on local richness and (4) considering the potential reciprocal effects of local processes on regional richness. In conclusion, we suggest some ways that similar approaches could be applied to other aspects of community structure beyond species richness.

Cultural diversity, economic development and societal instability.

Background: Social scientists have suggested that cultural diversity in a nation leads to societal instability. However, societal instability may be affected not only by within-nation or alpha diversity, but also diversity between a nation and its neighbours or beta diversity. It is also necessary to distinguish different domains of diversity, namely linguistic, ethnic and religious, and to distinguish between the direct effects of diversity on societal instability, and effects that are mediated by economic conditions.

Scale-dependent variation in coral community similarity across sites, islands, and island groups.

Community similarity is the proportion of species richness in a region that is shared on average among communities within that region. The slope of local richness (alpha diversity) regressed on regional richness (gamma diversity) can serve as an index of community similarity across regions with different regional richness. We examined community similarity in corals at three spatial scales (among transects at a site, sites on an island, and islands within an island group) across a 10 000-km longitudinal diversity gradient in the west-central Pacific Ocean.

Metacommunity models predict the local-regional species richness relationship in a natural system.

Many natural communities exhibit positive relationships between local and regional species richness (LSR-RSR relationships), which can be either linear or curvilinear. Previous models have shown that the form of this relationship depends on the relative rates of colonization and extinction and the sensitivity of these rates to competition. We use simple models to show that the LSR-RSR relationship also depends on the type of metacommunity structure (Levins-like or mainland-island), and our models generate a wider range of realistic forms than do most previous models.

Aggregation influences coral species richness at multiple spatial scales.

The spatial dispersion of individuals across multiple spatial scales can significantly influence biodiversity patterns. Here we characterize the dispersion of corals in reef assemblages distributed across a 10000-km longitudinal biodiversity gradient from Indonesia to the Society Islands, using a multiscale sampling design. Our results indicate that most coral species were aggregated among 10-m transect samples across this vast distance.

Invasion in a heterogeneous world: resistance, coexistence or hostile takeover?

We review and synthesize recent developments in the study of the invasion of communities in heterogeneous environments, considering both the invasibility of the community and impacts to the community. We consider both empirical and theoretical studies. For each of three major kinds of environmental heterogeneity (temporal, spatial and invader-driven), we find evidence that heterogeneity is critical to the invasibility of the community, the rate of spread, and the impacts on the community following invasion.

Coral communities are regionally enriched along an oceanic biodiversity gradient.

Ecological communities are influenced by processes operating at multiple scales. Thus, a better understanding of how broad- as well as local-scale processes affect species diversity and richness is increasingly becoming a central focus in modern community ecology. Here, in a study of unprecedented geographical scope, we show significant regional and local variation in the species richness of coral assemblages across an oceanic biodiversity gradient.

Herbivore responses to plant secondary compounds: a test of phytochemical coevolution theory.

Literature data were collected on the floristic distribution and toxicity of phytochemicals to herbivores and on herbivore specialization in order to test phytochemical coevolution theory. The theory makes four predictions that can be tested with this information. Herbivores can adapt to novel, more toxic chemicals by becoming specialists, or they can become generalists but at the cost of lower feeding success on any particular host.

Adult movement of the native holly leafminer, Phytomyza ilicicola Loew (Diptera: Agromyzidae): consequences for host choice within and between habitats.

Phytomyza ilicicola is a specialist herbivore, the larvae of which mine, and the adults of which feed and oviposit on the developing leaves of American Holly, Ilex opaca. Adult Phytomyza have been shown to discriminate among host plants on the basis of several host and habitat factors. Such discrimination may explain, in part, the observed density variation of larval Phytomyza among individual trees and between forest and suburban habitats.

The notion of minimum distance or why rare species are clumped.

The prevalence of statistical clumping in natural populations can sometimes obscure mutual avoidance behavior and the adaptive role of spacing out among population members. The problem is particularly severe in rare species where the inverse square relationship between expected nearest neighbor distance and population density demands mean distances between individuals be excessively large to maintain randomness or overdispersion. Realistically, individuals dispersing from a central nucleus might be expected to establish a minimum distance from neighbors to obtain a substantial gain in fitness but further dispersal would be undesirable due to increasing costs and decreasing gains.