Evolutionary ecology of specialization: insights from phylogenetic analysis

In this Special feature, we assemble studies that illustrate phylogenetic approaches to studying salient questions regarding the effect of specialization on lineage diversification. The studies use an array of techniques involving a wide-ranging collection of biological systems (plants, butterflies, fish and amphibians are all represented). Their results reveal that macroevolutionary examination of specialization provides insight into the patterns of trade-offs in specialized systems; in particular, the genetic mechanisms of trade-offs appear to extend to very different aspects of life history in different groups. In turn, because a species may be a specialist from one perspective and a generalist in others, these trade-offs influence whether we perceive specialization to have effects on the evolutionary success of a lineage when we examine specialization only along a single axis. Finally, how geographical range influences speciation and extinction of specialist lineages remains a question offering much potential for further insight.     

Versatility and specialization in labrid fishes: ecomorphological implications

Summary The term specialized has been used to describe species that possess unique functional attributes and/or a narrow, stereotyped range of attributes, but there are few comparative functional analyses of specialists and generalists. If species with functional morphological specializations are capable of functioning over a broad range, the link between morphology and ecology may be relaxed under certain environmental conditions. In this study, high-speed films of jaw movements during prey capture were compared statistically for three coexisting coral reef fish species in the family Labridae, one trophic specialist and two trophic generalists. The trophic specialist possessed a unique functional feature related to the movement of the hyoid in the floor of the mouth, while the trophic generalists were not observed to possess any functional specializations. All three species showed functional versatility in that they were able to adjust their prey capture mechanism in response to the evasive potential of the prey. The functional versatility of trophic specialists has implications for ecomorphological studies, since species characterized as possessing unique functional or morphological features may demonstrate marked flexibility in ecological variables such as diet or foraging behavior, decreasing the likelihood of identifying correlations between morphology and ecology.     

The behavioral ecology of sympatric African apes: implications for understanding fossil hominoid ecology

The behavioral ecology of the great apes is key evidence used in the reconstruction of the behavior of extinct ape and hominid taxa. Chimpanzees and gorillas have been studied in detail in the wild, and some studies of their behavioral ecology in sympatry have also been been carried out. Although the two ape species have divergent behavior and ecology in important respects, recent studies have shown that the interspecific differences are not as stark as previously thought and subsequently urge new consideration of how they share forest resources when sympatric. These new data require re-examination of assumptions about key aspects of chimpanzee-gorilla ecological divergence, such as diet, ranging and nesting patterns, and the mating system. Diet is a key component of the species adaptive complexes that facilitates avoidance of direct competition from the other. While the nutritional basis for chimpanzee food choice remains unclear and no doubt varies from site to site, this species is a ripe fruit specialist and ranges farther during periods of ripe fruit scarcity. Gorillas in the same habitat also feed on ripe fruit when widely available, but fall back onto fibrous plant foods during lean periods. The inclusion of animal protein in the diet of the chimpanzees and its absence in that of the gorillas also distinguish the species ecologically. It may also offer clues to aspects of ecological divergence among early members of the hominid phylogeny. The paper concludes by suggesting likely characteristics of sympatric associations of Pliocene hominids, based on field data from extant sympatric apes.     

Weed macaques: The evolutionary implications of macaque feeding ecology

Patterns of feeding ecology among the living macaques conform poorly with recognized phyletic distinctions within the genus because there is an important ecological division which cross-cuts phyletic groupings. This division, between weed species and non-weed species, is based on the differing abilities of macaques to tolerate and even prosper in close association with human settlements. Based on available information about their ecology in the wild, we tentatively assign macaque species to these two categories. Finally, we consider the implications of our argument for scenarios of the initial spread of the macaques.     

Using functional morphology to examine the ecology and evolution of specialization

Researchers strive to understand what makes species different,and what allows them to survive in the time and space that theydo. Many models have been advanced which encompass an arrayof ecological, evolutionary, mathematical, and logical principles.The goal has been to develop ecological theories that can, amongother things, make specific and robust predictions about howand where organisms should live and what organisms should utilize.The role of functional morphology is often an under-appreciatedparameter of these models. A more complete understanding ofhow anatomical features work to allow the organism to accomplishcertain tasks has allowed us to revisit some of these ideaswith a new perspective. We illustrate our view of this rolefor functional morphology in ecology by considering the issueof specialization: we attempt to align several definitions ofspecialization based upon shared ecological and evolutionaryprinciples, and we summarize theoretical predictions regardingwhy an organism might specialize. Kinematic studies of preycapture in several types of fishes are explored with regardto the potential ecological and evolutionary consequences ofspecialization, most notably in the area of trade-offs. We suggestthat a functional morphological perspective can increase ourunderstanding of the ecological concepts of specialization andit consequences. The kinds of data that functional morphologistscollect can help us to quantify organismal performance associatedwith specialization and the union of functional morphology withecology can help us to better understand not just how but whyorganisms interact in the manner that they do.     

Temporal stability of individual feeding specialization may promote speciation

1.  Inter-individual differences in trophic behaviour are considered important in the disruptive selection process for resource specialization and may represent an early phase in the evolution of polymorphism and adaptive radiation. Here, we provide evidence of high stability of individual trophic niches of a fish predator from a 15-year study.
2.  Individual resource specialization was investigated by combining data from analyses of stomach contents (recent trophic niche), trophically transmitted parasites (long-term niche) and trophic morphology (niche adaptations) from single specimens of a postglacial fish (Arctic charr) population sampled from contrasting pelagic and littoral habitats.
3.  Based on the relationships between morphology, parasites and diet, high inter-individual temporal consistency of narrow niches (zooplanktivorous vs . benthivorous) was evident through the ontogeny of the charr, indicating low degree of switching both in habitat utilization and feeding strategy of individual fish. Co-occurrence of differently specialized behavioural phenotypes was sustained over multiple generations.
4.  The stable long-term habitat and feeding specializations may represent an important initial step in an adaptive radiation process, and our findings suggest a case of sympatric speciation into two incipient forms diverging along the littoral–pelagic resource axis.     

The evolutionary ecology of individual phenotypic plasticity in wild populations

The ability of individual organisms to alter morphological and life-history traits in response to the conditions they experience is an example of phenotypic plasticity which is fundamental to any population's ability to deal with short-term environmental change. We currently know little about the prevalence, and evolutionary and ecological causes and consequences of variation in life history plasticity in the wild. Here we outline an analytical framework, utilizing the reaction norm concept and random regression statistical models, to assess the between-individual variation in life history plasticity that may underlie population level responses to the environment at both phenotypic and genetic levels. We discuss applications of this framework to date in wild vertebrate populations, and illustrate how natural selection and ecological constraint may alter a population's response to the environment through their effects at the individual level. Finally, we present future directions and challenges for research into individual plasticity.     

Density-dependent changes in individual foraging specialization of largemouth bass

 Individual foraging specializations are an important source of intraspecific variability in feeding strategies, but little is known about what ecological factors affect their intensity or development. We evaluated stomach contents in marked individual largemouth bass (Micropterus salmoides) and tested the hypothesis that diet specialization is most pronounced during periods with high conspecific densities. We collected diet data over 10 years from an unexploited population of largemouth bass that displayed a greater than threefold variation in density. Although diet composition of the aggregate bass population did not change during the study, bass body condition was inversely correlated with population size. Individual marked bass exhibited high diet consistency (diet overlap between successive captures) during years with high population densities. Diet overlap between randomly assigned pairs of bass was not correlated with population size. We did not detect the expected positive relationship between diet breadth and population size. Our analyses demonstrate that population responses to density changes may represent the sum of many unique individual foraging responses and would be obscured by pooled sampling programs. Behavioral flexibility of individuals may contribute to the ability of largemouth bass to function as a keystone predator in many aquatic communities. Received: 29 March 1996 / Accepted: 8 January 1997     

Foraging for light: photosensory ecology and agricultural implications

This mini-review is concerned with one of the facets of the sensory physiology of plants that, in the last decade, has been intensively studied using genetically altered plants and eco-physiological techniques – the perception of the proximity of neighbouring plants through specific informational photoreceptors. We focus on the signalling mechanisms that allow individual shoots to ‘forage’ for light in patchy and highly dynamic canopy environments. We present evidence from recent experiments suggesting that the fitness of each individual plant in the population, the growth of the population as a whole, and the degree of growth inequality among neighbours are all strongly dependent on the timing and precision of foraging mechanisms controlled, at least partially, by phytochrome-B-like phytochromes. This evidence is discussed in the context of potential impacts on yield of agricultural crops resulting from the artificial alteration of plant sensitivity to proximity photo-signals. Directed overexpression of phytochrome genes appears to be an interesting avenue to explore in order to alter the photomorphogenesis of specific organs (or developmental stages) without affecting the overall ability of the plants to forage for light.     

Behavioral implications of mechanistic ecology

Summary Mechanistic principles from engineering, meteorology, and soil physics are integrated with ecology and physiology to develop models for prediction of animal behavior. The Mojave Desert biome and the desert iguana are used to illustrate these principles.A transient energy balance model for animals in an outdoor environment is presented. The concepts and relationships have been tested in a wind tunnel, in a simulated desert, and in the field. The animal model requires anatomical information and knowledge of the thermoregulatory responses of the animal. The micrometeorological model requires only basic meteorological parameters and two soil physical properties as inputs. Tests of the model in the field show agreement between predicted and measured temperatures above and below the surface of about 2 to 3°C.The animal and micrometeorological models are combined to predict daily and seasonal activity patterns, available times for predator-prey interaction, and daily, seasonal and annual requirements for food and water. It is shown that food, water and the thermal environment can limit animal activity, and furthermore, the controlling limit changes with season. Actual observations of activity patterns and our predictions show close agreement, in many cases, and pose intriguing questions in those situations where agreement does not exist. This type of modeling can be used to further study predator-prey interactions, to study how changes in the environment might affect animal behavior, and to answer other important ecological and physiological questions.     

The community of an individual: implications for the community concept

The concept of the ecological community is examined from the perspective of its criteria and domain. The multiple definitions and uses of this concept indicate a variety of scales and approaches. In this paper, a core definition of the minimal criteria and domain is proposed. Using those criteria, a model of the ecological community is developed based on a focal individual and its interactions with other individuals. In order to increase the scale of the domain of this approach, additional criteria are required. This model is used to explore characteristics of the minimum domain and larger scales of the community concept. The structure that emerges emphasizes context dependency and the potential for indeterminacy for most types of interactions. A prominent historical argument, the nature of boundaries between communities, has no relevance in this model.     

On the concept of individual in ecology and evolution

Part of the art of theory building is to construct effective basic concepts, with a large reach and yet powerful as tools for getting at conclusions. The most basic concept of population biology is that of individual. An appropriately reengineered form of this concept has become the basis for the theories of structured populations and adaptive dynamics. By appropriately delimiting individuals, followed by defining their states as well as their environment, it become possible to construct the general population equations that were introduced and studied by Odo Diekmann and his collaborators. In this essay I argue for taking the properties that led to these successes as the defining characteristics of the concept of individual, delegating the properties classically invoked by philosophers to the secondary role of possible empirical indicators for the presence of those characteristics. The essay starts with putting in place as rule for effective concept engineering that one should go for relations that can be used as basis for deductive structure building rather than for perceived ontological essence. By analysing how we want to use it in the mathematical arguments I then build up a concept of individual, first for use in population dynamical considerations and then for use in evolutionary ones. These two concepts do not coincide, and neither do they on all occasions agree with common intuition-based usage.     

The community ecology of Aedes egg hatching: implications for a mosquito invasion

Abstract. 1. A recently introduced treehole mosquito from Asia, Aedes albopictus , is spreading throughout eastern North America, especially in tyre-refuse piles. Previous studies have identified inhibitory effects of larvae on egg hatch as a potential population regulatory mechanism within Aedes. Larva-egg interactions may also occur between species. This experiment assesses the ability of larvae of A. albopictus and two possible competitors in North America, A.triseriatus and A.aegypti , to suppress hatching of conspecific and congeneric eggs.
2. We exposed eggs of each species to varying combinations of larval species and density for 24h and assessed subsequent hatch rates. Aedes albopictus eggs exhibited the lowest level of inhibition when exposed to high larval densities; moreover, at the lowest larval density they imposed the most intense interspecific hatch inhibition.
3. Discretionary hatching in response to larval density may influence community composition by promoting the spread of A.albopictus , perhaps even leading to its dominance within North American Aedes communities.     

Understanding complex reproductive ecology in fishes: the importance of individual and population-scale information

Many riverine cyprinids native to the Great Plains of North America are members of a reproductive guild that broadcast spawns pelagic, semi-buoyant ova. The task of fully understanding and appreciating the complexity of the reproductive ecology of this guild has been difficult. Although various efforts to understand their reproductive ecology have been conducted over the last 60 years, the results of these studies and the conclusions drawn from them have been inconsistent and oftentimes seemingly contradictory. The result has been varied and ill-informed conservation and management strategies based on an incomplete understanding of the reproductive ecology of these fish. We used gonadosomatic index, oocyte development, oocyte size distribution, and histological techniques to assess the reproductive ecology of sharpnose shiner Notropis oxyrhynchus in the upper Brazos River, Texas, between April 2003 and March 2005. Histological analyses of ovarian tissue revealed that reproduction occurred over a six-month period between April and September during which individual fish spawned multiple times. Patterns in gonadosomatic index, oocyte development, and oocyte size distribution indicated that sharpnose shiner spawn asynchronously except during periods of increased streamflow when spawning is synchronized within populations. Reproductive ecology of the sharpnose shiner reported in this study appears to be nearly identical to that recently reported for two other broadcast spawning cyprinids in the Great Plains, indicating that a more complete and consistent understanding of their reproductive ecology is beginning to emerge. We attribute this to the inclusion of both individual and population-scale analyses used in the most recent studies.     

Some implications of paleoecology for contemporary ecology

The paleoecological record allows contemporary ecologists to put current phenomena into the context of a longer time-frame, thereby providing the opportunity to evaluate the importance of slowly operating processes, past cyclic or unusual events, disturbance regimes, and historically constrained phenomena. We briefly outline the environmental history of the Quaternary, discuss the spatial and temporal resolution of the paleoecological evidence for biotic change, and summarize data relevant to such current issues as the nature of the biotic community, the role of disturbance, stability versus rapid change, evolutionary theory, explanations of species diversity, and refugia theory. Finally, we offer examples of the utility of paleoecological techniques for ecologists and environmental scientists.