Age Resources Research Articles

The National Institute on Aging's Resource Centers for Minority Aging Research: Development, Evolution, and Impact.

Spanning nearly 30 of the 50 years in which the National Institute on Aging (NIA) has existed, the Resource Centers for Minority Aging Research (RCMAR) program represents one of the most successful initiatives for advancing minority aging research and diversifying the scientific workforce within the Institute and across the National Institutes of Health. This article celebrates the genesis of the RCMAR program, beginning with the need to enhance this work, ranging from theories underlying the then-nascent field of health disparities research to study design, measurement, and analytic procedures. It describes the companion focus on preparing, expanding, and diversifying generations of future scholars/scientists to carry forward these advances. RCMAR's emphasis on promoting a comprehensive approach to research career development and building supportive learning communities heralded a more holistic approach to training than was previously the case. The discussion describes the evolution of the structure and emphases of the RCMAR program as it has responded to the frequently changing political, funding, and research environments. The article concludes by highlighting the major successes of this initiative, the challenges it faces, and opportunities afforded future growth as individual centers, the program at large, and NIA as a whole continue to innovate as they collectively address the original goals which remain relevant today and in the near future.

Distance From Nest and Climate Explain Geographical Trends of Harvester Ant's Food Resource Use: A Multi‐Species Approach

ABSTRACTMainAnimals not only forage for abundant and nearby resources, but their diets can also be influenced by abiotic and geographic factors. This often results in non‐random interactions among species. We investigate how seed density, distance from nest, abiotic (e.g., climate stability, temperature, precipitation) and geographic factors (e.g., latitude, elevation and continental hemisphere) influence the removal of food items (i.e., seeds and dead arthropods) by Pogonomyrmex species.LocationSouth and North America, from Patagonia to the Rocky Mountains.TaxonGenus Pogonomyrmex (Formicidae: Hymenoptera).MethodsConducting standardised experiments, we performed a seed removal experiment and an assessment of the items retrieved by ant workers of 160 nests from eight Pogonomyrmex spp. at 16 sites extending the American continent.ResultsPogonomyrmex ants native to North America removed more seeds than their South American counterpart. In general, results align with optimal foraging theory, indicating a higher probability of seed removal near ant nests. High climate stability correlated with lower seed predation rates, emphasising seed consumption's significance in historically arid environments. Increased precipitation and temperature led to reduced removal of food resources, suggesting reduced water availability and lower mean temperatures increases the consumption of seeds by harvester ants.ConclusionsOverall, Pogonomyrmex ants' food resource use is influenced by a combination of factors such as region, distance from the nest and climate. This study underscores harvester ants' potential impact on plant distribution over large spatial scales consuming seeds from the immediate proximity of their nest and preventing establishment.

Patterns of deep fine root and water utilization amongst trees, shrubs and herbs in subtropical pine plantations with seasonal droughts.

Seasonal droughts will become more severe and frequent under the context of global climate change, this would result in significant variations in the root distribution and water utilization patterns of plants. However, research on the determining factors of deep fine root and water utilization is limited. We measured the fine root biomass and water utilization of trees, shrubs and herbs, and soil properties, light transmission, and community structure parameters in subtropical pine plantations with seasonal droughts. We found that the proportion of deep fine roots (below 1 m depth) is only 0.2-5.1%, but that of deep soil water utilization can reach 20.9-38.6% during the dry season. Trees improve deep soil water capture capacity by enhancing their dominance in occupying deep soil volume, and enhance their deep resource foraging by increasing their branching capacity of absorptive roots. Shrubs and herbs showed different strategies for deep water competition: shrubs tend to exhibit a "conservative" strategy and tend to increase individual competitiveness, while herbs exhibited an "opportunistic" strategy and tend to increase variety and quantity to adapt to competitions. Our results improve our understanding of different deep fine root distribution and water use strategies between overstory trees and understory vegetations, and emphasize the importance of deep fine root in drought resistance as well as the roles of deep soil water utilization in shaping community assembly.

Rock fragment content in soils shift root foraging behavior in xerophytic species

Root traits associated with resource foraging, including fine-root branching intensity, root hair, and mycorrhiza, may change in soils that vary in rock fragment content (RFC), while how these traits covary at the level of individual root branching order is largely unknown. We subjected two xerophytic species, Artemisia vestita (subshrub) and Bauhinia brachycarpa (shrub), to increasing RFC gradients (0%, 25%, 50%, and 75%, v v− 1) in an arid environment and measured fine-root traits related to resource foraging. Root hair density and mycorrhizal colonization of both species decreased with increasing root order, but increased in third- or fourth-order roots at high RFCs (50% or 75%) compared to low RFCs. The two species tend to produce more root hairs than mycorrhizas under the high RFCs. For both species, root hair density and mycorrhizal colonization intensity were negatively correlated with root length and root diameter across root order and RFCs. Rockiness reduced root branching intensity in both species comparing with rock-free soil. At the same level of RFC, A. vestita had thicker roots and lower branching intensity than B. brachycarpa and tended to produce more root hairs. Our results suggest the high RFC soil conditions stimulated greater foraging functions in higher root orders. We found evidence for a greater investment in root hairs and mycorrhizal symbioses as opposed to building an extensive root system in rocky soils. The two species studied, A. vestita and B. brachycarpa, took different approaches to foraging in the rocky soil through distinctive trait syndromes of fine-root components.

Individual‐resource network between Xylocopa bees and plant resources: generalist species, specialist individuals?

1. The resource partitioning hypothesis states that sympatric, morphologically, and functionally similar species can coexist by temporal separation or low food overlap. Also, the interindividual variations about the use of resources, i.e. individual specialisation, can promote the resilience and stability of their populations when an environmental disturbance affects food availability.2. Two sympatric and polylectic species of carpenter bees to test both the hypotheses of food niche partitioning and the occurrence of individual specialisation were used.3. The study was conducted in two Brazilian Savanna areas and the trophic niches of Xylocopa grisescens and X. frontalis were determined by the diversity of pollen types obtained from larval food samples. Individual‐resource networks were constructed to elucidate the patterns of resource use by the individuals of each species.4. The populations of the two bee species moderately overlapped their trophic niche. Xylocopa grisescens mainly used the pollen of non‐poricidal plants, whereas X. frontalis used pollen from plants with poricidal anthers. Individual‐resource networks of both species are weakly connected, highly specialised, and modular.5. In conclusion, the results suggest that the coexistence between Xylocopa grisescens and X. frontalis probably occurs due to food resource partitioning. Furthermore, the results about individual‐resource networks of both species seem to reveal the occurrence of interindividual variations regarding food resource foraging.

Ectomycorrhizal fungal communities differ among parental and hybrid Populus cross types within a natural riparian habitat

Plant hybridization is common and important in ecological and economic contexts, however little is known about the impact of plant hybridization on ectomycorrhizal fungal (EMF) communities in natural habitats. We used a Populus hybrid system ( P. angustifolia x P. fremontii ) in a heterogeneous riparian landscape to address the hypothesis that EMF communities differ among hybrids and their parental species (cross types). Several key results emerged. (1) Cross type influenced EMF composition, with communities on hybrids being distinct from their parents. (2) Cross type influenced the composition of hyphal exploration types important for soil resource foraging, although contact and short distance exploration types were dominant on all cross types. (3) Cross type had a marginal influence on EMF colonization, with P. angustifolia highest and P. fremontii lowest. These results highlight the potential for tree hybridization to structure belowground communities in heterogeneous natural ecosystems.

Non-invasive Imaging of Rice Roots in Non-compacted and Compacted Soil.

Roots are the prime organ for nutrient and water uptake and are therefore fundamental to the growth and development of plants. However, physical challenges of a heterogeneous environment and diverse edaphic stresses affect root growth in soil. Compacted soil is a serious global problem, causing inhibition of root elongation, which reduces surface area and impacts resource foraging. Visualisation and quantification of roots in soil is difficult due to this growth substrate's opaque nature; however, non-destructive imaging technologies are now becoming more widely available to plant and soil scientists working to address this challenge. We have recently developed an integrated approach, combining X-ray Computed Tomography (X-ray CT) and confocal microscopy to image roots grown in compacted soil conditions from a plant to a cellular scale. The method is suited to visualize cellular responses of root tips grown in both non-compacted and compacted soils. This protocol presents a fully integrated workflow, including soil column preparation, creation of compaction conditions, plant growth, imaging, and quantification of root adaptive responses at a cellular scale.

Species differ in worker body size effects on critical thermal limits in seed-harvesting desert ants (Messor ebeninus and M. arenarius)

Extreme temperatures can constrain foraging behavior, and individual differences in thermal tolerances may affect foraging performance within and among species. Ambient temperatures may thus mediate competitive interactions among species that share resources. Different species of desert seed-harvesting ants (genus Messor) forage for similar food resources, and colonies can overlap in foraging areas. Because Messor species differ in body size distributions, and thermal tolerance is often size related in ants, we hypothesized that body size differences within and between Messor species would predict individual variation in worker thermal tolerances. Body size effects on thermal physiology could have implications for interspecific competition. We measured tolerances of extreme high (maximum critical temperature or CTmax) and low temperatures (CTmin) in two Messor species simultaneously at the same study site, smaller bodied M. ebeninus and larger bodied M. arenarius. Although the species did not differ significantly in CTmin or CTmax, tolerance of high temperatures was significantly size dependent for M. ebeninus: worker tolerances of high temperatures decreased with body size in this species. The patterns suggest the foraging activity of the smallest workers of smaller bodied species could be more constrained by high ambient temperatures, which could impact the division of labor within colonies as well as interspecific interactions.

Climate and soil nutrients differentially drive multidimensional fine root traits in ectomycorrhizal‐dominated alpine coniferous forests

Abstract Fine root traits vary greatly with environmental changes, but the understanding of root trait variation and its drivers is limited over broad geographical scales, especially for ectomycorrhizal (ECM)‐dominated conifers in alpine forests. Herein, the covariation patterns of and environmental controls for fine root traits among ECM‐dominated conifers were examined to test whether and how climate and soil nutrients differentially affect fine root trait variations. Eight traits of first‐ and second‐order roots were measured, that is, root diameter (RD), specific root length (SRL), branching intensity (BRI), root tissue density (RTD), mycorrhizal colonization rate (MCR) and concentrations of carbon (C), nitrogen (N) and phosphorus (P), across 76 alpine coniferous populations on the eastern Tibetan Plateau, China. Our results showed that variations of the fine root traits fell into two major dimensions: the first dimension (32.39% of the total variance) was mainly represented by RD and SRL, potentially conveying a trade‐off between root life span and efficiency of resource foraging; the second dimension (23.70% of the variance) represented coordinated variation for root nutrients (i.e. N and P) and RTD, which depicts the conservation‐acquisition trade‐off in resource uptake, that is, root economic spectrum. Variations in RD and SRL were mainly driven by climatic variables, characterized by a significant increase in RD and a decrease in SRL with increasing mean annual precipitation. In contrast, variations in fine root nutrients (i.e. N and P) and RTD were primarily driven by soil fertility, showing a significant increase in root N and P concentrations but a decrease in RTD with increasing soil resource levels. Synthesis. Our study clearly shows two distinct dimensions of the variation of fine root traits in ECM‐dominated alpine coniferous forests, providing further evidence of the inherent multidimensionality of root traits. Moreover, our findings highlight different roles of climatic and soil variables in driving the variation of fine root traits, potentially leading to the multidimensionality of root traits. This study provides new insights for understanding and predicting shifts in plant belowground strategies in climate‐sensitive alpine forests world‐wide.

Spine and dine: A key defensive trait promotes ecological success in spiny ants.

A key focus of ecologists is explaining the origin and maintenance of morphological diversity and its association with ecological success. We investigate potential benefits and costs of a common and varied morphological trait, cuticular spines, for foraging behavior, interspecific competition, and predator–prey interactions in naturally co‐occurring spiny ants (Hymenoptera: Formicidae: Polyrhachis) in an experimental setting. We expect that a defensive trait like spines might be associated with more conspicuous foraging, a greater number of workers sent out to forage, and potentially increased competitive ability. Alternatively, consistent with the ecological trade‐off hypothesis, we expect that investment in spines for antipredator defense might be negatively correlated with these other ecological traits. We find little evidence for any costs to ecological traits, instead finding that species with longer spines either outperform or do not differ from species with shorter spines for all tested metrics, including resource discovery rate and foraging effort as well as competitive ability and antipredator defense. Spines appear to confer broad antipredator benefits and serve as a form of defense with undetectable costs to key ecological abilities like resource foraging and competitive ability, providing an explanation for both the ecological success of the study genus and the large number of evolutionary origins of this trait across all ants. This study also provides a rare quantitative empirical test of ecological effects related to a morphological trait in ants.

Bacterial foraging facilitates aggregation of Chlamydomonas microsphaera in an organic carbon source-limited aquatic environment

Microalgal aggregation is a key to many ecosystem functions in aquatic environments. Yet mechanistic understanding of microalgae aggregation, especially the interactions with ubiquitous bacteria populations, remains elusive. We reported an experimental study illustrating how the emerging bacterial populations interacted with a model microalga (Chlamydomonas microsphaera) cells and the consequent aggregation patterns. Results showed that the emergence of bacterial populations significantly stimulated C. microsphaera aggregation. Both bacterial and C. microsphaera motilities were remarkably excited upon coculturing, with the mean cell velocity being up to 2.67 and 1.80 times of those of separate bacterial and C. microsphaera cultures, respectively. The stimulated bacterial and C. microsphaera cell velocity upon coculturing would likely provide a mechanism for enhanced probability of cell-cell collisions that led to amplified aggregation of C. microsphaera population. Correlation analysis revealed that bacterial resource foraging (for polysaccharides) was likely a candidate mechanism for stimulated cell motility in an organic carbon source-limited environment, whereby C. microsphaera-derived polysaccharides serve as the sole organic carbon source for heterotrophic bacteria which in turns facilitates bacteria-C. microsphaera aggregation. Additional analysis showed that bacterial populations capable of successive decomposing algal-derived organic matters dominated the cocultures, with the top five abundant genera of Brevundimonas (24.78%), Shinella (17.94%), Sphingopyxis (11.62%), Dongia (5.82%) and Hyphomicrobium (5.45%). These findings provide new insights into full understanding of microalgae-bacteria interactions and consequent microbial aggregation characteristics in aquatic ecosystems.

THE STRENGTH OF WEAKER TIES: HAVE WE BEEN IGNORING A RESOURCE FOR AGING ADULTS?

The purpose of this study was to examine links between changes in social ties (close ties and weaker ties) and changes in positive and depressed affect across three waves in a large, representative sample of U.S. adults aged 40 and over (N = 802). Using trivariate dual-change score models, we found that a greater number of weaker ties was associated with higher numbers of close ties over time, and that the number of weaker ties was more strongly predictive of positive age-related changes in both aspects of well-being (i.e., less depressed affect and more positive affect) than the number of close ties. Our findings imply that focusing investment on the outer circles may have the unintended benefit of compensating for losses in the inner circle, and that contrary to popular theoretical orientations, weaker ties may offer older adults an avenue for both promoting positive affect and decreasing negative affect.

Coastal resource foraging, the culture of coastal livelihoods, and human well-being in Southeastern Puerto Rico: consensus, consonance, and some implications for coastal policy

Based on 3 years of fieldwork in Southeastern Puerto Rico (SE PR), we report on data showing that Puerto Rican coastal resource foragers (CR foragers) have a distinct cultural model of well-being, when compared with their non-foraging neighbors. The CR foragers’ cultural model of well-being is directly related to the foraging lifestyle. It emphasizes independence, investment in social relationships, and enjoyment of the natural environment over the more stable access to higher income available in the formal economy. As such, we view this cultural model as an alternative to the individualistic/capitalistic model of continual growth and wealth accumulation. Building on previous analysis in which we found higher subjective well-being for coastal resource foragers compared with non-foraging neighbors as reported by Garcia-Quijano et al. (J Anthropol Res 71 (2):145–167 2015), we find that the higher well-being of CR foragers compared with their non-foraging neighbors is consistent with Dressler’s (2018) framework of cultural consonance, in this case between what they value in life and what they are able to obtain through their occupation and lifestyle as CR foragers. We discuss the implication of our findings for coastal policy in CR foraging dependent locales such as SE PR.

A comparative morphometric study of sensory capacity in geometrid moths

Diet breadth and the degree of capital breeding have been established as major determinants of species-specific ecology of herbivorous insects. Both of these variables are related to resource foraging and therefore can be expected to have effects on sensory capacity. However, such effects have remained poorly studied, let alone in phylogenetically explicit multi-species comparisons. We contribute to filling this gap in a study of 60 species of geometrid moths (Lepidoptera: Geometridae), using adult head measures (eye size, antennal length and shape, forehead width) as indices of sensory capacity. When controlled for body size, eyes of the more capital breeding species (i.e. those with low contribution of adult feeding to reproduction) were found to be smaller, and female antennae shorter, than in income breeders. Feathery (vs simple filiform) male antennae were more frequently present in the capital breeders and in larger species. Regarding diet breadth, generalist species were found to have relatively wider male foreheads than specialists. The results suggest that (a) breeding strategy rather than diet breadth predicts sensory capacity in geometrids, (b) capital breeding (vs income breeding) is related to low sensory capacity in females, and (c) in contrast, males of the capital breeding species have evolved towards elevated olfactory capacity.

SIMULASI PRODUKSI HIJAUAN PADA TIPE UNIT SISTEM TIGA STRATA YANG BERBEDA

Nowadays, availability of forage for cattle and other animal protein resources getting less and less due to land changing functions. This will lead to increase in land price, decrease in animal productivities the will end on sustainability of the animal husbandry business. In Bali, farmers applied a Three Strata Forage System to provide forage along dry and rainy seasons. This study purpose was to find out forage production from four types but similar size of land (1 ha) which applied in that system, that were Type A (rectangle: 200 m x 50 m), Type B (L Form: 4 x (50 x 50 m), Type C (rectangle: 125 m x 80 m) and Type D (squares: 100 m x 100 m). This simulation showed that the forage production of the land was 14.533,805 ton DM/year for type A and B; 14.301,434 ton DM/year for Type C : and 14.276,171 ton/DM/year for Type D. It can be concluded that the land in similar size but differ in shape or type produce different quantity of forages. And addition forage production and carrying capacity were estimated below of recommended the three strata forage system.
 Keywords: Forages, production, three strata forage system

Soil multifunctionality and drought resistance are determined by plant structural traits in restoring grassland.

It is increasingly recognized that belowground responses to vegetation change are closely linked to plant functional traits. However, our understanding is limited concerning the relative importance of different plant traits for soil functions and of the mechanisms by which traits influence soil properties in the real world. Here we test the hypothesis that taller species, or those with complex rooting structures, are associated with high rates of nutrient and carbon (C) cycling in grassland. We further hypothesized that communities dominated by species with deeper roots may be more resilient to drought. These hypotheses were tested in a 3‐yr grassland restoration experiment on degraded ex‐arable land in southern England. We sowed three trait‐based plant functional groups, assembled using database derived values of plant traits, and their combinations into bare soil. This formed a range of plant trait syndromes onto which we superimposed a simulated drought 2 yr after initial establishment. We found strong evidence that community weighted mean (CWM) of plant height is negatively associated with soil nitrogen cycling and availability and soil multifunctionality. We propose that this was due to an exploitative resource capture strategy that was inappropriate in shallow chalk soils. Further, complexity of root architecture was positively related to soil multifunctionality throughout the season, with fine fibrous roots being associated with greater rates of nutrient cycling. Drought resistance of soil functions including ecosystem respiration, mineralization, and nitrification were positively related to functional divergence of rooting depth, indicating that, in shallow chalk soils, a range of water capture strategies is necessary to maintain functions. Finally, after 3 yr of the experiment, we did not detect any links between the plant traits and microbial communities, supporting the finding that traits based on plant structure and resource foraging capacity are the main variables driving soil function in the early years of grassland conversion. We suggest that screening recently restored grassland communities for potential soil multifunctionality and drought resilience may be possible based on rooting architecture and plant height. These results indicate that informed assembly of plant communities based on plant traits could aid in the restoration of functioning in degraded soil.

A synaptic threshold mechanism for computing escape decisions.

Escaping from imminent danger is an instinctive behaviour fundamental for survival that requires classifying sensory stimuli as harmless or threatening. The absence of threat allows animals to forage for essential resources, but as the level of threat and potential for harm increases, they have to decide whether or not to seek safety1. Despite previous work on instinctive defensive behaviours in rodents2–11, little is known about how the brain computes the threat level for initiating escape. Here we show that the probability and vigour of escape in mice scale with the saliency of innate threats, and are well described by a model that computes the distance between threat level and an escape threshold. Calcium imaging and optogenetics in the midbrain of freely behaving mice show that the activity of excitatory neurons in the deep layers of the medial superior colliculus (mSC) represents the threat stimulus saliency and is predictive of escape, whereas dorsal periaqueductal gray (dPAG) glutamatergic neurons encode exclusively the escape choice and control escape vigour. We demonstrate a feed-forward monosynaptic excitatory connection from mSC to dPAG neurons that is weak and unreliable – yet necessary for escape behaviour – which provides a synaptic threshold for dPAG activation and the initiation of escape. This threshold can be overcome by high mSC network activity because of short-term synaptic facilitation and recurrent excitation within the mSC, which amplifies and sustains synaptic drive to the dPAG. Thus, dPAG glutamatergic neurons compute escape decisions and vigour using a synaptic mechanism to threshold threat information received from the mSC, and provide a biophysical model of how the brain performs a critical behavioural computation.

Adaptive variation in vein placement underpins diversity in a major Neotropical plant radiation

Vein placement has been hypothesised to control leaf hydraulic properties, but the ecophysiological significance of variation in vein placement in the angiosperms has remained poorly understood. The highly diverse Neotropical Bromeliaceae offers an excellent system for exploring understudied relationships between leaf vein placement, physiological functions, and species ecology. To test key hypotheses regarding the links between vein placement, functional type divergences, and ecological diversity in the Bromeliaceae, I characterised the ratio of interveinal distance (IVD) to vein-epidermis distance (VED) in 376 species, representing all major functional types and 10% of the species diversity in the family, as well as bioclimatic properties and key leaf traits for subsets of species. There were significant differences in vein placement parameters in species of contrasting functional type, habitat association, and bioclimatic distribution. In many C3 tank-epiphytes, a greater ratio between interveinal distance and the depth of veins within the mesophyll reflects optimisation for resource foraging in shady, humid habitats. In succulent terrestrials, overinvestment in veins probably facilitates rapid recharge of water storage tissue, as well as restricting water loss. These results highlight how divergences in vein placement relate to distinctive ecophysiological strategies between and within bromeliad functional types, and provide timely insights into how structural–functional innovation has impacted the evolution of ecological diversity in a major radiation of tropical herbaceous angiosperms.

Social resource foraging is guided by the principles of the Marginal Value Theorem

Optimality principles guide how animals adapt to changing environments. During foraging for nonsocial resources such as food and water, species across taxa obey a strategy that maximizes resource harvest rate. However, it remains unknown whether foraging for social resources also obeys such a strategic principle. We investigated how primates forage for social information conveyed by conspecific facial expressions using the framework of optimal foraging theory. We found that the canonical principle of Marginal Value Theorem (MVT) also applies to social resources. Consistent with MVT, rhesus macaques (Macaca mulatta) spent more time foraging for social information when alternative sources of information were farther away compared to when they were closer by. A comparison of four models of patch-leaving behavior confirmed that the MVT framework provided the best fit to the observed foraging behavior. This analysis further demonstrated that patch-leaving decisions were not driven simply by the declining value of the images in the patch, but instead were dependent upon both the instantaneous social value intake rate and current time in the patch.

Edaphic resource foraging by Zostera marina (Linnaeus) patches

Clonal foraging in response to heterogeneously distributed water, light or mineral resources has been demonstrated for a number of terrestrial plant species. The existence of similar behavior in seagrasses and the cross-scale effects of clonal foraging on patch development, however, have not fully been explored. Our objective was to test whether spatial exploration by independent ramet clusters could generate emergent patch behavior consistent with clonal foraging theory. We also examined the effect of nutrient amendment on reproductive effort and seedling recruitment. Working in Shinnecock Bay, New York, USA, with the clonal marine angiosperm, Zostera marina, we attempted to stimulate directional growth along ten patch edges over a two-year period using subterranean fertilizer. Changes in ramet demography, patch expansion, seedling emergence and reproductive effort were quantified through repeated shoot censusing. We found that nutrient addition accelerated patch expansion. Enriched edges exhibited significantly higher shoot densities, indicating that a ramet proliferation, selective ramet placement or a combination of the two responses had occurred. The seasonality of this effect was different between treatments and consistent among years, representing a fundamental shift in the pattern and phenology of seagrass growth. Within patches, no detectable differences in per capita branching rates or reproductive effort were observed. This study provides the first evidence of foraging behavior by patches of Z. marina, and offers new insight into its seasonal growth patterns during the as yet poorly understood colonization period.