We review here factors that control the excitability of the giant neuron-mediated tail-flip escape behavior in crayfish, focusing especially on recent findings concerning serotonergic modulation. Serotonin can either facilitate or inhibit escape depending on concentration and pattern of application. Low concentrations facilitate while high ones inhibit; however, if high concentrations arise gradually they facilitate instead of inhibiting. The effects of serotonin can also be altered by social experience, with application regimens that cause facilitation in social isolates coming to produce inhibition after an extended period of living as a subordinate. Attempts to understand both the possible physiological basis of some of these complexities and their possible function are discussed. Neuroethological investigations indicate that giant neuron-mediated escape is inhibited during the initial fights that establish social relationships and is facilitated in their immediate aftermath. Once the relationship of a pair is well-established, the presence of the dominant tends to suppress giant neuron-mediated escape (but not tail-flip escape mediated by non-giant circuitry) in the subordinate, but the presence of the subordinate has relatively little effect on the dominant. These patterns of modulation can be seen as consistent with the known variations in serotonin's effect as a function of concentration and social experience and may provide a biological reason for these variations.

Previous models of behavioral choice have described two types of hierarchy, a decision hierarchy, in which different classes of decisions are made at each level (Tinbergen, 1951), and a behavioral hierarchy, in which one behavior will take precedence over others (Davis, 1985). Most experimental work on the neuronal basis of decision-making has focussed on the latter of these: a behavioral hierarchy is described for an animal, and the neuronal basis for this hierarchy, hypothesized to depend on inhibitory interactions, is investigated. Although the concept of “dedicated command neurons” has been useful for guiding these studies, it appears that such neurons are rare. We present evidence that in the leech, most neurons, including high-level decision neurons, are active in more than one behavior. We include data from one newly-identified neuron that elicits both swimming and crawling motor patterns. We suggest that decisions are made by a “combinatorial code”: what behavior is produced depends on the specific combination of decision neurons that are active at a particular time. Finally, we discuss how decision neurons may be arranged into a decision hierarchy, with neurons at each sequential level responsible for choosing between a narrower range of behaviors. We suggest additional sensory information is incorporated at each level to inform the decision.

Serotonin (5HT) induces short-term and long-term synaptic facilitation (STF and LTF, respectively) at sensory neuron to motor neuron (SN-MN) synapses in Aplysia, and these forms of plasticity are thought to contribute to short-term and long-term memory for behavioral sensitization. Recent evidence in Aplysia has identified a third phase of synaptic facilitation—intermediate-term facilitation (ITF)—that is temporally and mechanistically distinct from STF and LTF. Here, we review the findings of recent studies that have examined this unique intermediate-term phase at molecular, cellular, and behavioral levels. The results indicate that, at tail SN-MN synapses, multiple forms of ITF can be distinguished; they are induced via distinct mechanisms and use parallel molecular pathways for their expression. Moreover, we have incorporated the temporal and molecular features of these different forms of ITF at tail SN-MN synapses into behavioral analyses, and found that they accurately predict distinct forms of intermediate-term memory for sensitization of the tail-elicited siphon withdrawal reflex. These findings indicate that different types of experiences engage distinct molecular pathways in the service of memory retention over the same time domain.

Long-term facilitation (LTF) of Aplysia tail sensory neuron–motor neuron (SN–MN) synapses provides a synaptic correlate of memory for long-term behavioral sensitization of the tail-siphon withdrawal reflex. LTF can be induced by repeated exposures of serotonin (5HT) in the isolated pleural-pedal ganglion preparation. In addition, we have shown previously (Sherff and Carew, 1999) that LTF can also be induced by coincident 5HT exposure comprised of a single 25-min exposure of 5HT at the SN cell body and a 5 min pulse of 5HT at the SN-MN synapses. If synaptic 5HT is applied either 15 min before or after somatic 5HT, LTF is significantly reduced or is not induced at all. These results show that two anatomically remote cellular compartments can functionally interact within a surprisingly short time period. In this chapter, we discuss some of the mechanistic implications of this temporal constraint. We also find that coincident LTF and LTF induced by repeated pulses of 5HT differ (1) in whether they induce another temporal phase of facilitation (intermediate-term facilitation, ITF, expressed up to 1.5 hr after 5HT), and (2) in their requirements for protein synthesis. The results described both in this paper and in the preceding companion paper show that there are multiple forms of both ITF and LTF that differ in their induction and expression requirements, and at least in some instances, the different temporal phases of facilitation, and perhaps comparable phases of memory, can be induced independently of each other.

Four major questions can be asked about vertebrate brain evolution: 1) What major changes have occurred in neural organization and function? 2) When did these changes occur? 3) By what mechanisms did these changes occur? 4) Why did these changes occur? Comparative neurobiologists have been very successful in recognizing major changes in brain structure. They have also made progress in understanding the functional significance of these changes, although this understanding is primarily limited to sensory centers, rather than integrative or motor centers, because of the relative ease of manipulating the relevant stimuli. Although neuropaleontology continues to provide important insights into when changes occurred, this approach is generally limited to recognizing variation in overall brain size, and sometimes brain regions, as interpreted from the surface of an endocranial cast. In recent years, most new information regarding when neural changes occurred has been based on cladistical analysis of neural features in extant taxa. Historically, neurobiologists have made little progress in understanding how and why brains evolve. The emerging field of evolutionary developmental biology appears to be the most promising approach for revealing how changes in development and its processes produce neural changes, including the emergence of novel features. Why neural changes have occurred is the most difficult question and one that has been the most ignored, in large part because its investigation requires a broad interdisciplinary approach involving both behavior and ecology.

The span of complexity in brains, between the simplest flatworms and the most advanced mammals is exceedingly great, measured by the number of different anatomical parts, physiological processes, sensory discriminations, and behavioral alternatives in the repertoire. Most evolution of brains has been adaptive radiation within the same grade of complexity. Distinct grades of complexity have appeared a dozen or more times and quite often in the retrograde direction. Advancement has not been inevitable or obviously advantageous in survival value but has happened—long before primates or mammals or vertebrates. Compare cuttlefish and the most advanced gastropods, bees and the best brine shrimp, primates and the most advanced reptiles known—all twigs with common branches. This repeated achievement of evolution has had all too little study in respect of the detailed listing of differences between major taxa of distinct grades of complexity. Connectivity at the level now known for the mammalian cortex is much needed in other classes, with estimates of reciprocity, intrinsic differentiation, dendritic parcellation and afferent and efferent connections, both locally and projecting to other centers, each done quantitatively to permit comparison. Physiological system organization, personality properties of neurons and circuits, proclivities and emergent phenomena at several integrative levels are sketchily known only for parts of a few systems. Examples are given of opportunities for new research that can more adequately characterize grades of brains.

In animals, muscles are the most common effectors that translate neuronal activity into behavior. Nowhere is behavior more restricted by the limits of muscle performance than at the upper range of high-frequency movements. Here, we see new and multiple designs to cope with the demands for speed. Extremely rapid oscillations in force are required to power cyclic activities such as flight in insects or to produce vibrations for sound. Such behaviors are seen in a variety of invertebrates and vertebrates, and are powered by both synchronous and asynchronous muscles. In synchronous muscles, each contraction/relaxation cycle is accompanied by membrane depolarization and subsequent repolarization, release of activator calcium, attachment of cross-bridges and muscle shortening, then removal of activator calcium and cross-bridge detachment. To enable all of these to occur at extremely high frequencies a suite of modifications are required, including precise neural control, hypertrophy of the calcium handling machinery, innovative mechanisms to bind calcium, and molecular modification of the cross-bridges and regulatory proteins. Side effects are low force and power output and low efficiency, but the benefit of direct, neural control is maintained. Asynchronous muscles, in which there is not a 1:1 correspondence between neural activation and contraction, are a radically different design. Rather than rapid calcium cycling, they rely on delayed activation and deactivation, and the resonant characteristics of the wings and exoskeleton to guide their extremely high-frequency contractions. They thus avoid many of the modifications and attendant trade-offs mentioned above, are more powerful and more efficient than high-frequency synchronous muscles, but are considerably more restricted in their application.

The rocky intertidal zone is among the most physically harsh environments on earth. Marine invertebrates and algae living in this habitat are alternatively pounded by waves and exposed to thermal extremes during low tide periods (Denny and Wethey, 2001). Additionally, they must deal with strong selective pressures related to predation and competition for space (Connell, 1961). As a result, the steep physical gradient and spatially condensed community has made the rocky intertidal zone an ideal “natural laboratory” to study the coupled role of physical and biological factors in determining the abundance and distribution of organisms in nature (Connell, 1961; Paine, 1966, 1994).

Intertidal zonation, observed from earliest studies of the marine littoral zone, was first studied in the U.S. by ecologists with a botanical orientation. Using the physiological methods favored by Cowles, Clements, and Shelford, these early studies sought causal and deterministic explanations. By the 1930s, the limitations of these studies became apparent and ecologists returned to more descriptive approaches. With the creation of year round research laboratories on the west coast, ecologists soon shed the botanical orientation and began to adopt more stochastic and non-deterministic approaches to intertidal ecology, approaches that still characterize the research tradition.

Temperature's pervasive effects on physiological systems are reflected in the suite of temperature-adaptive differences observed among species from different thermal niches, such as species with different vertical distributions (zonations) along the subtidal to intertidal gradient. Among the physiological traits that exhibit adaptive variation related to vertical zonation are whole organism thermal tolerance, heart function, mitochondrial respiration, membrane static order (fluidity), action potential generation, protein synthesis, heat-shock protein expression, and protein thermal stability. For some, but not all, of these thermally sensitive traits acclimatization leads to adaptive shifts in thermal optima and limits. The costs associated with repairing thermal damage and adapting systems through acclimatization may contribute importantly to energy budgets. These costs arise from such sources as: (i) activation and operation of the heat-shock response, (ii) replacement of denatured proteins that have been removed through proteolysis, (iii) restructuring of cellular membranes (“homeoviscous” adaptation), and (iv) pervasive shifts in gene expression (as gauged by using DNA microarray techniques). The vertical zonation observed in rocky intertidal habitats thus may reflect two distinct yet closely related aspects of thermal physiology: (i) intrinsic interspecific differences in temperature sensitivities of physiological systems, which establish thermal optima and tolerance limits for species; and (ii) ‘cost of living’ considerations arising from sub-lethal perturbation of these physiological systems, which may establish an energetics-based limitation to the maximal height at which a species can occur. Quantifying the energetic costs arising from heat stress represents an important challenge for future investigations.

Vertical zonation of intertidal organisms, from the shallow subtidal to the supralittoral zones, is a ubiquitous feature of temperate and tropical rocky shores. Organisms that live higher on the shore experience larger daily and seasonal fluctuations in microhabitat conditions, due to their greater exposure to terrestrial conditions during emersion. Comparative analyses of the adaptive linkage between physiological tolerance limits and vertical distribution are the most powerful when the study species are closely related and occur in discrete vertical zones throughout the intertidal range. Here, I summarize work on the physiological tolerance limits of rocky intertidal zone porcelain crab species of the genus Petrolisthes to emersion-related heat stress. In the eastern Pacific, Petrolisthes species live throughout temperate and tropical regions, and are found in discrete vertical intertidal zones in each region. Whole organism thermal tolerance limits of Petrolisthes species, and thermal limits of heart and nerve function reflect microhabitat conditions. Species living higher in the intertidal zone are more eurythermal than low-intertidal congeners, tropical species have the highest thermal limits, and the differences in thermal tolerance between low- and high-intertidal species is greatest for temperate crabs. Acclimation of thermal limits of high-intertidal species is restricted as compared to low-intertidal species. Thus, because thermal limits of high-intertidal species are near current habitat temperature maxima, global warming could most strongly impact intertidal species.

The enhanced synthesis of heat-shock proteins (hsps), called the heat-shock (or stress) response, is activated when environmental stress denatures proteins. Hsp synthesis is activated at the upper temperatures of an organism's thermal range and is therefore thought to be critical for enhancing thermal tolerance limits in ectothermic animals. Here I show that the two temperate sister species T. brunnea and T. montereyi that occupy the subtidal and low-intertidal zone differ from the low- to mid-intertidal T. funebralis (and the subtropical mid-intertidal T. rugosa) in (i) heat tolerance, (ii) the onset temperature of their main hsp, hsp70 (70 kDa), (iii) the temperature of maximal hsp70 synthesis, (iv) the upper temperature of hsp synthesis, and (v) the recovery from a thermal stress typical for the mid-intertidal zone. A regulatory model in which hsps themselves regulate their own transcription and synthesis through a negative autoregulatory feedback mechanism can explain acclimation-induced but not interspecific variation in the onset temperature of hsp70 synthesis. Transplanting species across their vertical distribution limits showed that interspecific differences in the stress response are likely to prevent species occurring lower from inhabiting sites higher in the rocky intertidal zone. Endogenous levels of a hsp of a molecular mass of 72 kDa, hsp72, changed little with heat stress in a species' native thermal environment. The results therefore confirm the importance of interspecific differences in the stress response for setting limits to an organism's thermal environment. However, the role of hsps as short-term indicators of sublethal heat stress within a species' native thermal environment may be limited without a better understanding of their functional and regulatory characteristics.

The intertidal zone has historically functioned as an important natural laboratory for testing ideas about how physical factors such as temperature influence organismal physiology and in turn influence the distribution patterns of organisms. Key to our understanding of how the physical environment helps structure organismal distribution is the identification of physiological processes that have ecological relevance. We have focused on biochemical- and molecular-level physiology that would contribute to thermal tolerance and maintenance of a functional intracellular protein pool in the face of extreme and fluctuating environmental temperatures. Past research has addressed processes central to protein homeostasis (e.g., protein ubiquitination) and the molecular ecology of molecular chaperones, a.k.a. heat shock proteins (Hsps), in ectothermic animals. In this presentation, we focus on two new developments regarding the biology of heat shock proteins as molecular chaperones in intertidal organisms. First, we present data on the functional characteristics of the transcriptional factor, HSF1 and discuss how these data relate to the plasticity of Hsp gene expression observed in intertidal organisms in nature. Second, we present data on the biochemical function of heat shock proteins purified from our non-model study organisms and discuss the temperature relationships of these molecules as they assist in protein folding in situ.

An important step in connecting the organismal response to thermal stress to patterns of community structure is determining at what scale discernable levels of variation are manifested. The temperature signal to which organisms may potentially respond varies at many spatial scales including microhabitat, tidal height, site and latitude. A number of studies have taken physiological assessment of the heat shock response (HSR) into the intertidal both as a tool for examining the HSR in nature and for examining the utility of HSR molecules as population or community level indicators. Most commonly, immunodetection of the total pool of the Hsp70 family of isoforms is used. Here we present data on levels of Hsp70 in intertidal organisms from microhabitat to the mesoscale. Our data and previously published work show that Hsp70 levels vary at all scales examined, similar to other physical and biological variables of interest. This demonstrates both the potential utility of Hsp70 detection as a molecular tool for field biologists and to the care that must be taken in assessing scale of variation when looking for potential bioindicator molecules.

Different allozyme genotypes at the mannose phosphate isomerase (Mpi) locus in the northern acorn barnacle (Semibalanus balanoides) show a strong association with distinct intertidal microhabitats. In estuaries along the Maine Coast, the FF homozygote has higher fitness in exposed, high-tide level microhabitats while the SS homozygote has higher fitness under algal cover or at low-tide microhabitats. These patterns are consistent with a Levene (1953) model of balancing selection. In these same samples, polymorphisms at the glucose phosphate isomerase locus (Gpi) and mitochondrial DNA (mtDNA) show no fitness differences among microhabitats, providing intra-genomic controls supporting selection at or near Mpi. Here we report a similar analysis of genotype-by-microhabitat associations at sites in Narragansett Bay, Rhode Island, close to the southern range limit of S. balanoides. Genotype zonation at Mpi between high- and low-tide microhabitats is significantly different between Maine and Narragansett Bay due to opposite zonation patterns for the SF and FF genotypes. Enzyme activity data are consistent with this “reverse” zonation. At Gpi, there is significant microhabitat zonation in Narragansett Bay, while this locus behaves as a neutral marker in Maine. Mt DNA shows no significant microhabitat zonation in either Rhode Island or Maine. The Mpi data suggest that Levene-type selection for alternative genotypes in alternative habitats may operate at scales of both 10's of meters and 100's of kilometers. The Gpi data show how an apparently neutral locus can exhibit non-neutral variation under different environmental conditions. We argue that both Mpi and Gpi provide important genetic variation for adaptation to environmental heterogeneity that is recruited under distinct conditions of stress and carbohydrate substrate availability.

Recent advances in quantifying biochemical and cellular-level responses to thermal stress have facilitated a new exploration of the role of climate and climate change in driving intertidal community and population ecology. To fruitfully connect these disciplines, we first need to understand what the body temperatures of intertidal organisms are under field conditions, and how they change in space and time. Newly available data logger technology makes such an exploration possible, but several potential pitfalls must be avoided. Body temperature during aerial exposure is driven by multiple, interacting climatic factors, and extremes during low tide far exceed those during submersion. Moreover, because of effects of body size and morphology, two organisms exposed to identical climatic conditions can display very different body temperatures, which can also be substantially different from the temperature of the surrounding air. These same factors drive the temperature recorded by data loggers, and one logger type is unlikely to serve as an effective proxy for all organisms at a site. Here I describe the difficulties involved in quantifying patterns of body temperature in intertidal organisms, and explore the implications of this complexity for intertidal physiological ecology. I do so using data from temperature loggers designed to mimic the thermal characteristics of the mussel Mytilus californianus, and deployed at multiple sites along the West Coast of the United States. Results indicate a highly intricate pattern of thermal stress, where the interaction of climate with the dynamics of the tidal cycle determines the timing and magnitude of temperature extremes, creating a unique “thermal signal” at each site.

One aspect of the physiological ecology of intertidal organisms is their mechanical design, which can be explored at many hierarchical levels, from molecules to ecosystems. Mechanical structures, as with any other physiological feature, require energy to construct and maintain, are subject to manufacturing and evolutionary constraints, and influence ecological performance. This contribution focuses on the ecomechanics of mussel attachment, which contributes to the competitive dominance of mussels on many wave-swept shores. Examples are presented to illustrate the hierarchical nature of mussel attachment, how levels of the hierarchy are interrelated, and where gaps in our knowledge remain. For example, water motion generates forces that mechanically deform byssal threads, but may also enhance the rate at which threads subsequently restore their original toughness. Furthermore, the ability of mussels to sense and respond to changes in their flow environment by producing a stronger attachment may be subject to physiological constraints, which in turn may have important consequences for the ecological response of mussels to shifts in wave climate. Thus an integrative approach to the study of byssal attachment is needed to fully understand this important aspect of the physiological ecology of mussels on rocky intertidal shores.

Populations of marine benthic organisms occupy habitats with a range of physical and biological characteristics. In the intertidal zone, energetic costs increase with temperature and aerial exposure, and prey intake increases with immersion time, generating size gradients with small individuals often found at upper limits of distribution. Wave action can have similar effects, limiting feeding time or success, although certain species benefit from wave dislodgment of their prey; this also results in gradients of size and morphology. The difference between energy intake and metabolic (and/or behavioral) costs can be used to determine an energetic optimal size for individuals in such populations. Comparisons of the energetic optimal size to the maximum predicted size based on mechanical constraints, and the ensuing mortality schedule, provides a mechanism to study and explain organism size gradients in intertidal and subtidal habitats. For species where the energetic optimal size is well below the maximum size that could persist under a certain set of wave/flow conditions, it is probable that energetic constraints dominate. When the opposite is true, populations of small individuals can dominate habitats with strong dislodgment or damage probability. When the maximum size of individuals is far below either energetic optima or mechanical limits, other sources of mortality (e.g., predation) may favor energy allocation to early reproduction rather than to continued growth. Predictions based on optimal size models have been tested for a variety of intertidal and subtidal invertebrates including sea anemones, corals, and octocorals. This paper provides a review of the optimal size concept, and employs a combination of the optimal energetic size model and life history modeling approach to explore energy allocation to growth or reproduction as the optimal size is approached.

Rocky intertidal invertebrates live in heterogeneous habitats characterized by steep gradients in wave activity, tidal flux, temperature, food quality and food availability. These environmental factors impact metabolic activity via changes in energy input and stress-induced alteration of energetic demands. For keystone species, small environmentally induced shifts in metabolic activity may lead to disproportionately large impacts on community structure via changes in growth or survival of these key species. Here we use biochemical indicators to assess how natural differences in wave exposure, temperature and food availability may affect metabolic activity of mussels, barnacles, whelks and sea stars living at rocky intertidal sites with different physical and oceanographic characteristics. We show that oxygen consumption rate is correlated with the activity of key metabolic enzymes (e.g., citrate synthase and malate dehydrogenase) for some intertidal species, and concentrations of these enzymes in certain tissues are lower for starved individuals than for those that are well fed. We also show that the ratio of RNA to DNA (an index of protein synthetic capacity) is highly variable in nature and correlates with short-term changes in food availability. We also observed striking patterns in enzyme activity and RNA/DNA in nature, which are related to differences in rocky intertidal community structure. Differences among species and habitats are most pronounced in summer and are linked to high nearshore productivity at sites favored by suspension feeders and to exposure to stressful low-tide air temperatures in areas of low wave splash. These studies illustrate the great promise of using biochemical indicators to test ecological models, which predict changes in community structure along environmental gradients. Our results also suggest that biochemical indices must be carefully validated with laboratory studies, so that the indicator selected is likely to respond to the environmental variables of interest.

Geographic limits of species are commonly associated with climatic or physical boundaries, but the mechanisms of exclusion at the limits of distribution are poorly understood. In some intertidal populations, the strengths of interactions with natural enemies are mediated by microclimate, and determine geographic limits. The northern limit of the barnacle Chthamalus fragilis in New England is the south side of Cape Cod, Massachusetts. South of the cape, Chthamalus has a refuge from competition in the high intertidal, which is too hot for survival of its superior competitor Semibalanus balanoides. North of the cape, the high intertidal is cooler, and Semibalanus survives, so Chthamalus has no refuge. Thus, geographic variation in the strength of competition may determine the geographic limit of Chthamalus. Intolerance of cold by Chthamalus cannot account for the geographic limit: transplants of Chthamalus 80 km beyond its northern limit survived up to 8 yr in the absence of competition with Semibalanus. At the geographic limit of Chthamalus in the Cape Cod Canal there are two bridges, 5 km apart. On the southern bridge, Chthamalus is abundant and occupies a refuge above Semibalanus. On the northern bridge in 2001, only 7 individual Chthamalus were present. Despite the proximity of the bridges, their microclimates are very different. The southern bridge, where Chthamalus is abundant, is up to 8°C hotter than the northern bridge. This higher temperature creates a refuge in the high intertidal for Chthamalus. On the cooler northern bridge, there is no refuge for Chthamalus. Because of the difference in temperatures of the water masses that meet in the canal, heat storage in the rock of the bridge piers causes the temperatures to differ between the bridges. Thus, geographic change in microclimate alters the strength of competition, and determines the geographic limit.

Ecologists and physiologists working on rocky shores have emphasized the effects of environmental stress on the distribution of intertidal organisms. Although consumer stress models suggest that physical extremes may often reduce predation and herbivory through negative impacts on the physiological performance of consumers, few field studies have rigorously tested how environmental variation affects feeding rates. I review and analyze field experiments that quantified per capita feeding rates of a keystone predator, the sea star Pisaster ochraceus, in relation to aerial heat stress, wave forces, and water temperature at three rocky intertidal sites on the Oregon coast. Predation rates during 14-day periods were unrelated to aerial temperature, but decreased significantly with decreasing water temperature. There was suggestive but inconclusive evidence that predation rates also declined with increasing wave forces. Data-logger records suggested that thermal stress was rare in the wave-exposed habitats that I studied; sea star body temperatures likely reached warm levels (>24°C) on only 9 dates in 3 yr. In contrast, wind-driven upwelling regularly generated 3 to 5°C fluctuations in water temperature, and field and laboratory results suggest that such changes significantly alter feeding rates of Pisaster. These physiological rate effects, near the center of an organism's thermal range, may not reduce growth or fitness, and thus are distinct from the effects of environmental stress. This study underscores the need to consider organismal responses both under “normal” conditions, as well as under extreme conditions. Examining both kinds of responses is necessary to understand how different components of environmental variation regulate physiological performance and the strength of species interactions in intertidal communities.

Environmental stress and nutrient/productivity models predict the responses of community structure along gradients of physical conditions and bottom-up effects. Although both models have succeeded in helping to understand variation in ecological communities, most tests have been qualitative. Until recently, two roadblocks to more quantitative tests in marine environments have been a lack of (1) inexpensive, field-deployable technology for quantifying (e.g.) temperature, light, salinity, chlorophyll, and productivity, and (2) methods of quantifying the sub-organismal mechanisms linking environmental conditions to their ecological expression. The advent of inexpensive remote-sensing technology, adoption of molecular techniques such as quantification of heat-shock proteins and RNA:DNA ratios, and the formation of interdisciplinary alliances between ecologists and physiologists has begun to overcome these roadblocks. An integrated eco-physiological approach focuses on the determinants of: distributional limits among microhabitat patches and along (local-scale) environmental gradients (e.g., zonation); among-site (mesoscale) differences in community pattern; and geographic (macroscale) differences in ecosystem structure. These approaches promise new insights into the physiological mechanisms underlying variation in processes such as species interactions, physical disturbance, survival and growth. Here, we review two classes of models for community dynamics, and present examples of ecological studies of these models in consumer-prey systems. We illustrate the power of new molecular tools to characterize the sub-organismal responses of some of the same consumers and prey to thermal stress and food concentration. Ecological and physiological evidence tends to be consistent with model predictions, supporting our argument that we are poised to make major advances in the mechanistic understanding of community dynamics along key environmental gradients.