Joan Roughgarden

A LATITUDINAL GRADIENT IN RECRUITMENT OF INTERTIDAL INVERTEBRATES IN THE NORTHEAST PACIFIC OCEAN

A latitudinal gradient in the recruitment rates of intertidal mussels and barnacles was detected in the Northeast Pacific during 1996 and 1997. This gradient was approximately a stepcline: annual recruitment, on average, was 1-2 orders of magnitude higher in central and northern Oregon than in central and northern California. In contrast to the regional differences, large-scale gradients in recruitment within California were small: correlations of recruitment with latitude were weak, and, in all but one case, statistically insignificant. Nonetheless, trends in the data suggest that recruitment within central and northern California was highest between San Francisco and Monterey Bay, where larvae may be retained more nearshore than to the north or south. If so, apparently conflicting claims about latitudinal gradients in recruitment within California can be reconciled. The large scale transition in recruitment rates supports the hypothesis that a marked shift in the intensity of upwelling near Cape Blanco in southern Oregon is a major cause of a coincident transition in community structure. Stronger upwelling (and thus offshore flow) to the south has been hypothesized to transport larvae further offshore and thereby reduce larval supply to nearshore benthic communities. This study confirms that the predicted differences in recruitment exist, and that these differences are large. Preliminary calculations indicate that regional differences in offshore flow are likely to make a larger contribution to the recruitment transitions than several other plausible causes. In addition, recruitment transitions are larger, more abrupt, and more consistent across species than corresponding shifts in percentage cover, which favor competitive dominants. This supports model predictions that competition for space is more intense where recruitment is high. However, the absence of strong, large-scale recruitment gradients within California suggests that mesoscale processes are relatively more important than latitudinal trends in upwelling as determinants of community structure patterns at smaller scales.

No-take Reserve Networks: Sustaining Fishery Populations and Marine Ecosystems

Abstract Improved management approaches are needed to reduce the rate at which humans are depleting exploited marine populations and degrading marine ecosystems. Networks of no-take marine reserves are promising management tools because of their potential to (1) protect coastal ecosystem structure and functioning, (2) benefit exploited populations and fisheries, (3) improve scientific understanding of marine ecosystems, and (4) provide enriched opportunities for non-extractive human activities. By protecting marine ecosystems and their populations, no-take reserve networks can reduce risk by providing important insurance for fishery managers against overexploitation of individual populations. Replicated reserves also foster strong scientific testing of fishery and conservation management strategies. Reserve networks will require social acceptance, adequate enforcement, and effective scientific evaluation to be successful. Processes for reserve establishment should accommodate adaptive management so bounda...

THEORY OF MARINE COMMUNITIES: COMPETITION, PREDATION, AND RECRUITMENT‐DEPENDENT INTERACTION STRENGTH

Of the marine animals that spend their adult lives inhabiting benthic communities, most have a planktonic larval phase. In this paper, we derive the relationship between the physical oceanographic processes that transport these larvae and the strength of species interactions in the benthic habitat. We review a model of hierarchical competition for space between two species with planktonic larvae and develop a model for predator–prey dynamics in which prey are space-limited. Lotka-Volterra approximations to these models are developed. The approximations provide per capita interaction strength (the effect of an individual of one species on the per capita growth rate of another) and population interaction strength (the effect of a population of one species on the per capita growth rate of another) as functions of parameters in the original model. Per capita and population interaction strengths of dominant competitors on subordinates decrease in magnitude as offshore advection of larvae increases. The per cap...

The Impact of Directed versus Random Movement on Population Dynamics and Biodiversity Patterns

An improved understanding of dispersal behavior is needed to predict how populations and communities respond to habitat fragmentation. Most spatial dynamic theory concentrates on random dispersal, in which movement rates depend neither on the state of an individual nor its environment and movement directions are unbiased. We examine the neglected dispersal component of directed movement in which dispersal is a conditional and directional response of individuals to varying environmental conditions. Specifically, we assume that individuals bias their movements along local gradients in fitness. Random movers, unable to track heterogeneous environmental conditions, face source‐sink dynamics, which can result in deterministic extinction or increase their vulnerability to stochastic extinction. Directed movers track environmental conditions closely. In fluctuating environments, random movers “spread their bets” across patches, while directed movers invest offspring in habitats currently enjoying propitious conditions. The autocorrelation in the environment determines each strategy’s success. Random movers permeate entire landscapes, but directed movers are more geographically constrained. Local information constraints limit the ranges of directed movers and introduce a role for historical contingency in determining their ultimate distribution. These geographic differences have implications for biodiversity. Random movement maintains biodiversity through local coexistence, but directed movement favors a spatial partitioning of species.

A FRAMEWORK FOR ASSESSING THE RELATIVE VULNERABILITY OF SPECIES TO LAND‐USE CHANGE

Conversion of native habitat to human-dominated uses is the main driver of global biodiversity loss, yet which species will be most impacted, and why, remain poorly known. There is thus an urgent need to develop frameworks for understanding, and pre- dicting, the effect of habitat alteration on biodiversity. We develop an approach with three components: a demographic model, a regional database of life-history traits, and a sensitivity analysis of the model predictions. We use a spatially explicit model that predicts the fate of individual species in a human-dominated landscape. The model takes as parameters habitat affinity, population growth rate, annual dispersal, and dispersal behavior at the habitat edges. The model predicts the minimum area of native habitat that allows for persistence of a species. We apply the model to a regional community of species, the avifauna of Costa Rica. We gather life-history data (body mass, clutch size, breeding season length, number of broods per year, age at first breeding, life span, and dispersal distance) for Costa Rican birds. When data are not available for Costa Rican species, inferences are made from North American and European birds. We use these data to estimate the model parameters for each species. Minimum patch sizes predicted by the model are used to specify the relative degree of threat faced by each species. We perform a sensitivity analysis of patch size and relative vulnerability predictions to model assumptions and gaps in the data. Our predictions of relative vulnerability are robust to changes in model assumptions and agree with an independently derived empirical assessment. Our framework thus appears to be useful for understanding, and influencing, the fates of neotropical birds and possibly other taxa worldwide.

WHAT IS AN INDIVIDUAL ORGANISM? A MULTILEVEL SELECTION PERSPECTIVE

Most biologists implicitly define an individual organism as “one genome in one body.” This definition is based on physiological and genetic criteria, but it is problematic for colonial organisms. We propose a definition based instead on the evolutionary criteria of alignment of fitness, export of fitness by germ‐soma specialization, and adaptive functional organization. We consider how these concepts apply to various putative individual organisms. We conclude that complex multicellular organisms and colonies of eusocial insects satisfy these three criteria, but that, in most cases (with at least one notable exception), colonies of modular organisms and genetic chimeras do not. While species do not meet these criteria, they may meet the criteria for a broader concept—that of an evolutionary individual—and sexual reproduction may be a species‐level exaptation for enhancing evolvability. We also review the costs and benefits of internal genetic heterogeneity within putative individuals, demonstrating that high relatedness is neither a necessary nor a sufficient condition for individuality, and that, in some cases, genetic variability may have adaptive benefits at the level of the whole.

Biodiversity conservation: Effects of changes in climate and land use

Arising from: C. D. Thomas et al. 427, 145–148 (2004)); see also communication from Thuiller et al. and communication from Harte et al.; Thomas et al. replyThomas et al. argue, contrary to Sala et al., that climate change poses an equal or greater threat to global biodiversity than land-use change. We contest this claim, however, on the grounds that Thomas et al. incorrectly apply species–area relationships.

The economic value of ecological stability

Seemingly intangible ecosystem characteristics that preoccupy ecologists, like ecosystem stability and the responsiveness of populations to environmental variation, have quantifiable economic values. We show how to derive these values, and how their consideration should change environmental decision making. To illustrate these concepts, we use a simple reserve design model. When resource managers choose a particular landscape configuration, their decision affects both the mean abundance of species and the temporal variation in abundances. Population stability and related phenomena have economic value, because management actions affect the variance of ecosystem components. In our example, a larger reserve size is recommended when accounting for the stability of the managed ecosystem.

An invitation to ecological economics.

The emerging interdisciplinary field of ecological economics should be a recognized research priority. Only through a combination of sound ecology and good economics can we hope to manage our exploitation of the biosphere in a manner that is both sustainable and efficient. This article is an invitation to ecologists to use economic tools and to participate in ecological economic debate. To this end, we review basic ecological economic concepts and discuss how the field has arisen, what benefits it offers, and what challenges it must overcome.

Do we need a Sexual Selection 2.0

Sexual selection is one of Darwin’s major contributions to evolutionary biology. However, it has been subjected to repeated controversy, including our own recent challenge (Roughgarden et al. 2006), which has provoked lively debate (Kavanagh 2006; Clutton-Brock 2007). In response, Clutton-Brock (2009) proposes to extend the theory of sexual selection to females in a manner parallel to that for males, and Carranza (2009) proposes to redefine sexual selection theory. We refer to both of these proposals collectively as ‘Sexual Selection 2.0’. In this paper we show that Clutton-Brock’s extension of the theory to females exacerbates the problems with standard sexualselection theory, compounding the errors already present when the theory is applied specifically to males.We also show that Carranza’s redefinition of sexual selection violates the basic canon of science that once a hypothesis has been falsified, it shall not be redefined to render it true in light of new data, a process that, if allowed, would render any hypothesis infinitely malleable and thus untestable. Overall, we find that replacing the standard theory of sexual selection with some updated version 2.0 is inadvisable. Instead, we note that our proposal for an altogether new theory to replace sexual selection avoids compounding existing errors, is testable, and is possibly correct. Below, we consider the two papers separately.