Shifts In Resource Use Research Articles

Electricity supply and demand scenarios for the Southern African power pool

The study presents long-term electricity supply and demand scenarios for the twelve countries in the Southern African Power Pool, based on detailed bottom-up demand analysis for all countries and a set of internally consistent development scenarios. Total regional electricity demand and supply increase by eight to fourteen times from 2010 to 2070, with major shifts in both the sectoral composition of demand and the geography of demand, with South Africa becoming a much smaller share. On the supply side, the fuel mix shifts from coal and toward hydro in the medium term, but towards other renewables, such as solar, in the longer term, particularly in the scenarios with the fastest decline in capital costs for renewables. This leads to declining unit carbon dioxide emissions in the more aggressive scenarios, even though total power sector emissions still increase. The unit cost of generation for the entire region is stable across all scenarios. The potential transformation of the supply sector would require a fundamental shift in resource use, grid management and infrastructure development in the region, as well as greater regional integration. This also implies significant institutional capacity development in the SAPP Coordination Centre or similar structures for cooperative management of resources.

Exploitation of marine resources by wolves in southwestern Alaska

Predation by large carnivores is a dominant factor shaping wildlife communities and an understanding of local foraging strategies of predators is central to the management of wildlife populations. Information on local foraging strategies is particularly important where carnivores might exploit alternate resources that could influence predator–prey interactions, carnivore population dynamics, and a variety of interactions at lower trophic levels. We used carbon (δ13C) and nitrogen (δ15N) values in serially sampled wolf ( Canis lupus ) vibrissae to quantify relative resource use and dietary variation among wolves ( n = 115) from 4 areas in southwestern Alaska that differed in the availability of terrestrial and marine resources. Mean vibrissae isotope values varied by ~8‰ for δ13C and ~12‰ for δ15N and showed high levels of spatial, seasonal, and individual variation. While results showed that ungulates were the principal prey for wolves in all 4 areas, wolves also exploited a variety of alternate marine resources that represented an important component of wolf diets in some areas. Estimated dietary contributions from marine resources ranged from 28% to 56% among areas and use of these resources varied both spatially and seasonally. Dietary variation and use of marine resources increased from northeast to southwest along the Alaska Peninsula with increasing access to coastal areas and decreasing ungulate abundance. Seasonal shifts in resource use were also evident with dietary variation being highest during summer and fall when wolves consumed more alternate resources than during winter. Our findings suggest that use of marine resources and local variation in foraging strategies of wolves might, through a variety of pathways, have broad implications for the management of wolf–ungulate communities in southwestern Alaska.

State-dependent capital and income breeding: a novel approach to evaluating individual strategies with stable isotopes.

BackgroundSpecies-specific strategies for financing the costs of reproduction are well understood, forming a continuum ranging from high to low reliance on stored nutrients. Animals relying mostly on stored reserves are termed ‘capital breeders’, whereas ‘income breeders’ rely mostly on concurrent intake when financing the costs of reproduction. The role and adaptive value of individual variation in these strategies remain elusive. Life-history theory posits that capital breeding should be favoured when offspring reproductive value peaks, typically occurring early in the season, and that current income should increasingly be used with progressing season. Because resource limitation may hamper flexible resource allocation, a corollary prediction is that only good-condition individuals may show the expected seasonal shift in resource use. To test this prediction, we examined stable isotopes (δ13C and δ15N) in blood and lipid-free egg yolk of breeding eider females (Somateria mollissima) from the Baltic Sea to assess the role of individual variation in the use of proteins from local diet vs. stored reserves.ResultsWe show for the first time that individuals from a single population differ in their utilization of stored reserves and concurrent intake to finance the costs of reproduction. Consistent with our prediction, heavy females predominantly used stored reserves for producing egg yolks early in the season, increasingly relying on local feeding with later onset of breeding, whereas light females showed no seasonal change in allocation strategy.ConclusionsStable isotope profiling at the individual level is a powerful tool for monitoring relative changes in investment strategies through time, showing promise as an early warning indicator of ecological change in food webs.

A comparative perspective on the ecology of morphological diversification in complex societies: nesting ecology and soldier evolution in the turtle ants

This work uses a comparative framework to address the adaptive evolutionary relationship between nesting ecology and the morphological diversification of the soldier caste in turtle ants (Cephalotes). Turtle ant colonies nest in pre-existing arboreal cavities, and soldiers specialize in colony defense by blocking cavity entrances with their armored heads. Analyses were focused on three major axes of soldier morphological diversification: discrete morphotype, head size, and head-size range (i.e., soldier polymorphism). The analyses showed that while all species use some entrances small enough to fit the head of one soldier, specialization on entrances that tightly fit the head of one soldier was only seen in species with the most specialized soldier morphotype. They also showed that the degree of soldier polymorphism was only positively correlated with the typical range of entrances in species with the most specialized morphotype. Overall, these findings indicated that a tight 1:1 size-matching between available soldier head sizes and selected entrance sizes is limited to species with the most specialized soldier morphotype, while species with less specialized morphotypes use a broader range of larger entrances. Together, these findings suggest a new general hypothesis for the adaptive diversification of caste systems: major shifts in ecological specialization drive the evolution of novel caste morphotypes, while minor expansions and contractions of an existing resource range shape the evolution of the size distribution of an existing caste. Broadly, these findings highlight the possibility for complex coupling and decoupling between different axes of caste diversification in lineages with complex social phenotypes. One key way in which complex "organismal societies" have diversified in form and function is via the evolution of morphologically distinct "castes" that specialize on particular social roles. Nevertheless, how ecological interactions shape caste diversification within social lineages remains poorly understood. Using a comparative framework, this work addresses how nesting ecology has shaped the diversification of an elaborate soldier caste in the turtle ants. The evolution of more specialized soldier types was associated with substantial shifts in nest-entrance specialization, while in species with the most specialized soldier type, there was also a match between head sizes and entrance sizes within and across species. These findings suggest the general hypothesis that the evolution of novel caste types is driven by major shifts in ecological specialization, while the size distribution of existing castes tracks minor shifts in resource use.

Stable isotope characterization of Rainy River, Ontario, lake sturgeon diet and trophic position

Abstract Lake sturgeon ( Acipenser fulvescens ) are considered threatened and many populations have declined since the early 1890s. Limited food web studies have been conducted with lacustrine lake sturgeon populations while similar studies do not exist for riverine populations. We use stable isotope analysis to study the diet composition of lake sturgeon captured in the Rainy River, Ontario. Historical reports of lake sturgeon consumption of fish and fish eggs exist, but both prey have largely been considered as a minor contribution to the overall diet of lake sturgeon. More recent dietary studies have focused on juvenile sturgeon and report low or no incidence of fish or fish eggs in lake sturgeon diets. The results of the stable isotope studies of Rainy River lake sturgeon suggest they obtain a large portion of their energy from organic material derived directly or indirectly from fish. Results parallel those recently reported for adult sturgeon in Lake Winnebago, Wisconsin, and are important in the context of contributing modern technical verification to earlier historical reports of fish and fish eggs in lake sturgeon diets. The results of this study provide evidence of potential seasonal or temporal shifts in lake sturgeon diet and further evidence to the potential shift in resource use based on life stage. Estimates of isotopic niches for the Rainy River sturgeon establish an important baseline for future changes in food web structure that might accompany the introduction of invasive species or the addition of anthropogenic stressors that could have implications for lake sturgeon conservation.

Dietary overlap and seasonality in three species of mormoopid bats from a tropical dry forest.

Competing hypotheses explaining species' use of resources have been advanced. Resource limitations in habitat and/or food are factors that affect assemblages of species. These limitations could drive the evolution of morphological and/or behavioural specialization, permitting the coexistence of closely related species through resource partitioning and niche differentiation. Alternatively, when resources are unlimited, fluctuations in resources availability will cause concomitant shifts in resource use regardless of species identity. Here, we used next-generation sequencing to test these hypotheses and characterize the diversity, overlap and seasonal variation in the diet of three species of insectivorous bats of the genus Pteronotus. We identified 465 prey (MOTUs) in the guano of 192 individuals. Lepidoptera and Diptera represented the most consumed insect orders. Diet of bats exhibited a moderate level of overlap, with the highest value between Pteronotus parnellii and Pteronotus personatus in the wet season. We found higher dietary overlap between species during the same seasons than within any single species across seasons. This suggests that diets of the three species are driven more by prey availability than by any particular predator-specific characteristic. P.davyi and P.personatus increased their dietary breadth during the dry season, whereas P.parnellii diet was broader and had the highest effective number of prey species in all seasons. This supports the existence of dietary flexibility in generalist bats and dietary niche overlapping among groups of closely related species in highly seasonal ecosystems. Moreover, the abundance and availability of insect prey may drive the diet of insectivores.

Ontogenetic shifts in resource use by the sea urchin Evechinus chloroticus across an ecotone

Ontogenetic shifts in resource use by the sea urchin Evechinus chloroticus across an ecotone

Interaction patterns within a multi-herbivore assemblage derived from stable isotopes

The ecological effects of consumer guilds are strongly driven by the relative resource use of included species. Here we use stable isotopes in faecal samples from 6 co-occurring mammalian herbivores in an African savanna to identify species-specific trophic niches and detect patterns of interactions between herbivores and their feeding resources. Species-specific foraging strategies were reflected in the faecal δ13C values, with species aligning along both a browser-grazer gradient and a niche breadth gradient. Within the broad foraging strategies outlined by δ13C, δ15N indicated a seasonal shift in resource use for some herbivores. We expected that 13C isotope niches would overlap in a nested fashion, with the niches of grazers and browsers being included in those of mixed feeders, and that 15N niches would separate into discrete modules reflecting leguminous and protein content of respective diets. However, the observed structure was more complex, with combined modular and nested patterns of interactions between herbivores and 13C isotopes. We identified an isolated module comprising eland and its exclusive δ13C values, and a series of nested structures with a set of specialist herbivores (hartebeest and sable) which δ13C values were nested within those of more generalist herbivores (impala, waterbuck and zebra). Networks based on δ15N, however, reflected a higher level of overlap in resource use with random patterns in herbivore interactions with resources, and only a significant modular interaction pattern during the dry season. We suggest that the combined modular and nested pattern of δ13C interactions reflect the simultaneous mutualistic and antagonistic characteristics of plant–herbivore interactions. We argue that such interaction patterns could stabilize ecosystems by constraining effects of perturbations to specific modules and by increasing functional redundancy through nested interactions.

A colourful youth: ontogenetic colour change is habitat specific in the invasive Nile perch

External body colour is an important trait contributing to phenotypic diversity and individual fitness in fish species. In this study, we use a combination of experimental techniques and field observations to examine patterns of colour divergence in the introduced Nile perch population of Lake Nabugabo, Uganda. We aim to determine whether the proportion of black–brown body colouration of Nile perch differs over a number of size classes, across ecologically distinct wetland edge and forest edge habitats, and whether these differences are the result of rapid (physiological) or ontogenetic (morphological) colour change. We found substantial colour differences in Nile perch between habitats, but trends were not consistent across size classes. Small Nile perch ( 40 cm SL) Nile perch. Inter-habitat differences in colour in the small size class, and shifts in colour from juvenile to adult appear to be the result of morphological colour change associated with distinct ontogenetic shifts in resource use.

Habitat partitioning and morphological differentiation: the Southeast Asian Draco lizards and Caribbean Anolis lizards compared

Sympatric species that initially overlap in resource use are expected to partition the environment in ways that will minimize interspecific competition. This shift in resource use can in turn prompt evolutionary changes in morphology. A classic example of habitat partitioning and morphological differentiation are the Caribbean Anolis lizards. Less well studied, but nevertheless striking analogues to the Anolis are the Southeast Asian Draco lizards. Draco and Anolis have evolved independently of each other for at least 80 million years. Their comparison subsequently offers a special opportunity to examine mechanisms of phenotypic differentiation between two ecologically diverse, but phylogenetically distinct groups. We tested whether Draco shared ecological axes of differentiation with Anolis (e.g., habitat use), whether this differentiation reflected interspecific competition, and to what extent adaptive change in morphology has occurred along these ecological axes. Using existing data on Anolis, we compared the habitat use and morphology of Draco in a field study of allopatric and sympatric species on the Malay Peninsula, Borneo and in the Philippines. Sympatric Draco lizards partitioned the environment along common resource axes to the Anolis lizards, especially in perch use. Furthermore, the morphology of Draco was correlated with perch use in the same way as it was in Anolis: species that used wider perches exhibited longer limb lengths. These results provide an important illustration of how interspecific competition can occur along common ecological axes in different animal groups, and how natural selection along these axes can generate the same type of adaptive change in morphology.

Synchronized peak-rate years of global resources use

Many separate studies have estimated the year of peak, or maximum, rate of using an individual resource such as oil. However, no study has estimated the year of peak rate for multiple resources and investigated the relationships among them. We exploit time series on the appropriation of 27 global renewable and nonrenewable resources. We found 21 resources experienced a peak-rate year, and for 20 resources the peak-rate years occurred between 1960-2010, a narrow time window in the long human history. Whereas 4 of 7 nonrenewable resources show no peak-rate year, conversion to cropland and 18 of the 20 renewable resources have passed their peak rate of appropriation. To test the hypothesis that peak-rate years are synchronized, i.e., occur at approximately the same time, we analyzed 20 statistically independent time series of resources, of which 16 presented a peak-rate year centered on 2006 (1989-2008). We discuss potential causal mechanisms including change in demand, innovation and adaptation, interdependent use of resources, physical limitation, and simultaneous scarcity. The synchrony of peak-rate years of multiple resources poses a greater adaptation challenge for society than previously recognized, suggesting the need for a paradigm shift in resource use toward a sustainable path in the Anthropocene.

Ontogenetic changes in shell preferences and resource partitioning by the hermit crabs Pagurus hirsutiusculus and P. granosimanus

Ontogenetic shifts in resource use can serve to reduce mortality and intraspecific competition, but can also increase a population's likelihood of extinction. We examined the ontogeny of shell type (i.e. snail species) preferences as well as shell type usage in the field in 2 sympatric species of intertidal hermit crabs, Pagurus hirsutiusculus and P. granosimanus, on Vancouver Island, Canada. An experiment examining shell type preferences by 4 hermit crab size classes, spanning a broad range of juvenile and adult sizes, found that both species have well-defined shell type preferences throughout benthic life; shell type occupancy at 7 field sites was largely consistent with shell type preferences. In addition, shell type preferences in both species changed during ontogeny, in terms of the preferred shell types but also in the diversity of shell types that were used, which decreased with increasing crab size. Thus, as a cohort of hermit crabs grows from newly settled juveniles to full-sized adults, the availability of suitable shells will depend on different snail species; shell availability at different stages of ontogeny would thus be controlled by independent mechanisms. In addition, similar-sized hermit crabs of the 2 species mostly ignored the shell types used by the other species, a resource partitioning that would facilitate coexistence. If shell availability limits the local abundance of these hermit crab species, as previously suggested, our findings indicate they would be limited by different resources (i.e. shells produced by different snail species). The lack of correlation between the abundance estimates of the 2 species at our 7 field sites supports the hypothesis that the local abundance of P. hirsutiusculus and P. granosimanus is controlled by independent factors.

Becoming a Patient-Centered Medical Home: A 9-Year Transition for a Network of Federally Qualified Health Centers

The patient-centered medical home (PCMH) model has great potential for optimizing the care of chronically ill patients, yet there is much to be learned about various implementations of this model and their impact on patient care processes and outcomes. We examined changes in patterns of health care use in a network of Federally Qualified Health Centers throughout a 9-year period of practice transformation that included recognition of all centers by the National Committee for Quality Assurance (NCQA) as Level 3 PCMH practices. We analyzed deidentified data from electronic health records for the period 2003 to 2011 to identify patterns of service use for all 4,595 patients with diabetes. We also examined a subsample of 545 patients who were in care throughout the study period to track improvement in glycated hemoglobin levels as a clinical measure over time. Through the transition to a PCMH, the mean number of encounters with outreach, diabetes educators, and psychosocial services increased for all diabetic patients; virtually all patients had visits with a primary care clinician, but the mean number of visits decreased slightly. Among patients in the subsample, mean annual levels of glycated hemoglobin decreased steadily during the 9-year study period, mainly driven by a reduction in patients having baseline levels exceeding 9%. This retrospective study conducted in a real-world setting using electronic health record data demonstrates a shift in resource use by diabetic patients from the primary care clinician to other members of the care team. The findings suggest that PCMH implementation has the potential to alter processes of care and improve outcomes of care, especially among those with higher disease burden.

Does shade cover availability limit nest-site choice in two populations of a turtle with temperature-dependent sex determination?

Shifts in resource use may be an important mechanism by which organisms can adjust to novel environmental conditions, such as those imposed by climate change. However, for such shifts to be possible, environmental space must exist into which organisms can move. Habitat that ensures successful survival and reproduction is one such critical resource. We studied resource selection of shade cover over nest sites by painted turtles in populations in Illinois (center of range) and New Mexico (southern edge of range). We targeted this habitat feature because shade can influence hatching success and offspring phenotype (including sex in the study species) by affecting nest microenvironments. We found that while turtles in both populations selected nest sites that were shadier than average available sites, overall resource selection differed between the populations. This disparity may have been due to differences in structure of vegetation that provides shade at each site, because areas with high shade cover in New Mexico (low dense thickets) were much more difficult for turtles to access than those in Illinois (dense tree canopy cover). Further, shade cover predicted different parameters of incubation regime at each site, suggesting that turtles must assess dissimilar components of shade cover in order to choose nest sites and predict their future incubation regimes. Our results suggest that shade cover within nesting areas is a key component of painted turtle habitat, and that accessible, highly-shaded nest sites may be limited at the New Mexico site. Maintaining a range of shade cover from which turtles can select nest sites would permit plasticity in nest-site choice to be expressed, which may be important in preventing sex ratio skews due to climate change.

High variability in spatial and temporal size-based trophodynamics of deep-sea fishes from the Mid-Atlantic Ridge elucidated by stable isotopes

Demersal fish play an important role in the deep-sea ecosystem by acting as a link to mobile food in the water column, consuming benthic fauna, breaking down large food parcels and dispersing organic matter over large areas. Poor diet resolution from stomach content analysis often impairs the ability to assess differences in inter- and intra-population trophodynamics and therefore understand resource partitioning among deep-sea fishes. Antimora rostrata (predator–scavenger), Coryphaenoides armatus (predator–scavenger), Coryphaenoides brevibarbis (predator) and Halosauropsis macrochir (predator) were collected from 3 stations on the Mid-Atlantic Ridge (MAR) in 2007 and 2009 to investigate trophic ecology using δ13C and δ15N. Variability in lipid-normalised δ13C (δ13Cn) and δ15N was explained by body length in all species but slope and significance of the isotope–length relationships varied both temporally and spatially. δ15N increases with length were observed in A. rostrata at all stations, C. brevibarbis and H. macrochir at one or more stations but were absent in C. armatus. δ13Cn increased with length in A. rostrata but the slope of δ13Cn–length relationships varied spatially and temporally in C. armatus and C. brevibarbis. The co-occurring δ13Cn and δ15N size-based trends in A. rostrata and H. macrochir suggested that size-based trends were a result of increasing trophic position. In C. armatus and C. brevibarbis the isotope-length trends were difficult to distinguish among trophic position increases, shifts in resource use i.e. benthic to pelagic or internal physiology. However, the overall strength, direction and significance of isotope-length trends varied temporally and spatially which suggested varying degrees of overlap in trophic ecology and feeding plasticity among these species.

Host conservatism, host shifts and diversification across three trophic levels in two Neotropical forests

Host-parasite systems have been models for understanding the connection between shifts in resource use and diversification. Despite theoretical expectations, ambiguity remains regarding the frequency and importance of host switches as drivers of speciation in herbivorous insects and their parasitoids. We examine phylogenetic patterns with multiple genetic markers across three trophic levels using a diverse lineage of geometrid moths (Eois), specialist braconid parasitoids (Parapanteles) and plants in the genus Piper. Host-parasite associations are mapped onto phylogenies, and levels of cospeciation are assessed. We find nonrandom patterns of host use within both the moth and wasp phylogenies. The moth-plant associations in particular are characterized by small radiations of moths associated with unique host plants in the same geographic area (i.e. closely related moths using the same host plant species). We suggest a model of diversification that emphasizes an interplay of factors including host shifts, vicariance and adaptation to intraspecific variation within hosts.

Differing perspectives of major oil firms on future energy developments: An illustrative framework

This study develops a framework to analyse the perspectives of major oil firms in terms of their perceptions of current energy developments and projections of future energy potentials, and illustrates their views on the possibility of a paradigm shift in fuel use. The three A's themes—availability of resource (AV), applicability of technology (AP) and acceptability by society (AC)—make up the analytical framework. Divergence in oil firms’ behaviour and perspectives are captured by the 3-A triangle that illustrates how the four largest oil firms in the world balance their stakes among the three A's. ExxonMobil's position is markedly skewed towards the theme of AV, whilst BP has the most balanced approach among the four. Shell and Total both share a similarly shaped 3-A triangle with more stakes placed on the theme of AP. The results would imply that a paradigm shift in resource use or a full-scale transition to a backstop technology is unlikely in the coming decades.

PLANT UPTAKE OF INORGANIC AND ORGANIC NITROGEN: NEIGHBOR IDENTITY MATTERS

The importance of interspecific competition as a cause of resource partitioning among species has been widely assumed but rarely tested. Using neighbor removals in combination with 15N tracer additions in the field, we examined variation among three alpine species in the uptake of 15N-NH4+, 15N-NO3-, and 15N-13C-[2]-glycine in intact neighborhoods, when paired with a specific neighbor, and when all neighbors were removed. Species varied in the capacity to take up 15N-labeled NH4+, NO3-, and glycine in intact neighborhoods and in interspecific pairs. When interspecific neighbor pairs were compared with no neighbor controls, neighbors reduced 15N uptake in target species by as much as 50%, indicating competition for N. Furthermore, neighbor identity influenced the capacity of species to take up different forms of N. Thus, competition within interspecific neighbor pairs often caused reduced uptake of a particular form of N, as well as shifts to uptake of an alternative form of N. Such shifts in resource use as a result of competition are an implicit assumption in studies of resource partitioning but have rarely been documented. Our study suggests that plasticity in the uptake of different forms of N may be a mechanism by which cooccurring plants reduce competition for N.

ECOLOGICAL OPPORTUNITY AND PHENOTYPIC PLASTICITY INTERACT TO PROMOTE CHARACTER DISPLACEMENT AND SPECIES COEXISTENCE

We investigated the roles of resource availability and phenotypic plasticity in promoting ecological character displacement (i.e., trait evolution stemming from resource competition between species). Because ecological character displacement generates new populations that differ in resource use, this process should only occur when exploitable resources are available. We tested this hypothesis in two species of spadefoot toads (Spea bombifrons and S. multiplicata) whose tadpoles use phenotypic plasticity to develop into either an omnivore morph, which specializes on detritus, or a physically distinctive carnivore morph, which specializes on shrimp. Both species grow best on shrimp, but when reared together, S. bombifrons outcompetes S. multiplicata for shrimp and S. multiplicata outcompetes S. bombifrons for detritus. We found that when each species occurred alone in the field, they produced similar proportions of omnivores and carnivores. When the two species occurred together, however, they underwent ecological character displacement in larval development, with S. multiplicata producing mostly omnivores, and S. bombifrons producing mostly carnivores. We combined observations of natural populations with experiments to evaluate whether such character displacement was only possible when both shrimp and detritus were relatively abundant. Mixed-species ponds contained abundant detritus and shrimp, in contrast with nearby pure-species ponds, which were deficient in one resource. Experiments revealed that S. multiplicata competed poorly when detritus was rare and that S. bombifrons competed poorly when shrimp was rare. In nature, when one of these two resources was scarce, one species was missing, perhaps through competitive exclusion by the species that was the superior competitor for the remaining resource. Thus, ecological character displacement and, therefore, coexistence of close competitors, was only possible when diverse resources were available. Finally, even if exploitable resources are available, character displacement is not guaranteed to transpire if species cannot utilize such resources expeditiously. Phenotypic plasticity provides a general and important mechanism for facilitating resource partitioning. Thus, by facilitating shifts in resource use, phenotypic plasticity and ecological opportunity may often interact to promote divergence and coexistence of competitors.

Biomass allocation, growth, and photosynthesis of genotypes from native and introduced ranges of the tropical shrub Clidemia hirta.

We tested the hypothesis that the tropical shrub Clidemia hirta appears more shade tolerant and is more abundant in its introduced than native range because of genetic differences in resource acquisition, allocation, and phenotypic plasticity between native and introduced genotypes. We examined growth, biomass allocation, and photosynthetic parameters of C. hirta grown in a greenhouse from seed collected from four populations in part of its native range (Costa Rica) and four populations in part of its introduced range (Hawaiian Islands). Six-month-old seedlings were placed in high (10.3-13.9 mol m(-2) day(-1)) or low (1.4-4.5 mol m(-2) day(-1)) light treatments and grown for an additional 6 months. Our study provided little evidence that Hawaiian genotypes of C. hirta differed genetically from Costa Rican genotypes in ways that would contribute to differences in habitat distribution or abundance. Some of the genetic differences that were apparent, such as greater allocation to stems and leaf area relative to whole plant biomass in Costa Rican genotypes and greater allocation to roots in Hawaiian genotypes, were contrary to predictions that genotypes from the introduced range would allocate more biomass to growth and less to storage than those from the native range. Hawaiian and Costa Rican genotypes displayed no significant differences in relative growth rates, maximal photosynthetic rates, or specific leaf areas in either light treatment. In the high light environment, however, Hawaiian genotypes allocated more biomass to reproductive parts than Costa Rican genotypes. Phenotypic plasticity for only 1 of 12 morphological and photosynthetic variables was greater for Hawaiian than Costa Rican genotypes. We conclude that genetic shifts in resource use, resource allocation, or plasticity do not contribute to differences in habitat distribution and abundance between the native and introduced ranges of C. hirta.