Changes In Growth Rate Research Articles

Course‐based Undergraduate Research Linked Across Two Core Biology Courses

Authentic mentored undergraduate research is known to improve student learning and engagement. Course‐based undergraduate research experiences (CUREs) allow more students to participate in research early in their academic careers. We are expanding the CURE concept by linking research projects across two distinct yet interdependent courses required for the Biology major, Cell Biology and Intermediate Genetics. Each course enrolls 130‐150 students per year and may be taken in either order. To support successful projects, we first mentored upper level students in the development of protocols and generation of strains that could be employed to explore metabolic strategies in the aquatic ciliate Tetrahymena thermophila. In a pilot of a linked CURE, students investigated whether exogenous addition of oleate, an unsaturated fatty acid, alters the phenotype of T. thermophila.Students in Cell Biology examined changes in growth rate, metabolism, and lipid storage using light and fluorescent microscopy, thin layer chromatography, and spectrophotometry. Students in Intermediate Genetics examined changes in gene expression with both qualitative and quantitative RT‐PCR. Students in our linked CUREs responded to their lab experience with enthusiasm for participation in novel research, and curiosity about the research results gathered in the other of the linked courses. Future offerings of linked CUREs will expand the number of students that engage with a year‐long research project using multiple approaches to address a single question. Importantly, this approach is adaptable to different questions and model organisms, providing a template for sustainable research opportunities.

Spatial variability of microzooplankton grazing on phytoplankton in coastal southern Florida, USA.

Microzooplankton are considered the primary consumers of phytoplankton in marine environments. Microzooplankton grazing rates on phytoplankton have been studied across the globe, but there are still large regions of the ocean that are understudied, such as sub-tropical coastal oceans. One of these regions is the coastal area around south Florida, USA. We measured microzooplankton grazing rates in two distinct environments around south Florida; the oligotrophic Florida Keys and the mesotrophic outflow from the Everglades. For 2-years from January 2018 to January 2020, we set up 55 dilution and light-dark bottle experiments at five stations to estimate the microzooplankton community grazing rate, instantaneous phytoplankton growth rate, and primary production. Our results suggest that microzooplankton are consuming a higher proportion of the primary production near the Everglades outflow compared to the Florida Keys. We also found that changes in phytoplankton growth rates are disconnected from changes in the microzooplankton grazing rates in the Florida Keys. Overall, the data from the Everglades outflow is what would be expected based on global patterns, but factors other than microzooplankton grazing are more important in controlling phytoplankton biomass in the Florida Keys.

Nutrient and salt depletion synergistically boosts glucose metabolism in individual Escherichia coli cells

The interaction between a cell and its environment shapes fundamental intracellular processes such as cellular metabolism. In most cases growth rate is treated as a proximal metric for understanding the cellular metabolic status. However, changes in growth rate might not reflect metabolic variations in individuals responding to environmental fluctuations. Here we use single-cell microfluidics-microscopy combined with transcriptomics, proteomics and mathematical modelling to quantify the accumulation of glucose within Escherichia coli cells. In contrast to the current consensus, we reveal that environmental conditions which are comparatively unfavourable for growth, where both nutrients and salinity are depleted, increase glucose accumulation rates in individual bacteria and population subsets. We find that these changes in metabolic function are underpinned by variations at the translational and posttranslational level but not at the transcriptional level and are not dictated by changes in cell size. The metabolic response-characteristics identified greatly advance our fundamental understanding of the interactions between bacteria and their environment and have important ramifications when investigating cellular processes where salinity plays an important role.

Ontogeny of the American alligator (Alligator mississippiensis) prenatal head: A morphometric approach.

Variation in vertebrate cranial morphology is both extensive and functionally significant. Morphometric analysis attempts to explain such variation in form in evolutionary and functional contexts. Developmental morphometric analyses of vertebrate crania are less common, and many taxa are underrepresented. For example, the published morphometric studies of crocodilian cranial development focus mainly on posthatchling head development, with few, incomplete morphometric analyses of prehatchling heads. To further explore ontogenetic changes in the alligator head, we recorded and analyzed six linear cranial measurements in 77 preserved embryonic and hatchling American alligators (Alligator mississippiensis) representing 20 different stages. Examination of individual measurements revealed nonlinear changes in growth rate during development, suggesting a level of dynamic complexity worthy of further analysis. Using principal components analysis,we identified three distinct phases in prenatal alligator head growth. The second (intermediate) phase disrupts an otherwise monotonic developmental trajectory and represents a phase of reduced snout growth. Although this is a detailed description of prehatchling ontogenetic trajectory of the alligator head, further studies in other crocodilians are needed to assess evolutionary patterns among crocodilians.

REVIVING THE KLANG VALLEY ECONOMY DURING PANDEMIC THROUGH DIGITALISATION OF THE MARITIME LOGISTICS INDUSTRY

The maritime logistics industry is an international business ecosystem and backbone of Malaysia’s economic development. Due to the COVID-19 pandemic, we have witnessed a drastic decline of industries all over the world, which may take a very long time to recover. This paper discusses the digital transformation of the maritime logistics industry based in the Klang Valley of Peninsular Malaysia as a strategic plan to improve existing business processes and make it resilient in face of the challenges brought on by the pandemic. We evaluated the digitalisation practices of maritime logistics companies to identify enablers that can help restore the economy as the industry tries to move on under the shadow of COVID-19. The Fuzzy Delphi (FD) method is used to collect and analyse data based on the response of 18 experts with more than five years of industry experience. A total of 15 key enablers were determined and ranked in terms of priority, with the top three being changes in the long-term industry growth rate, marketing innovation and implementation of digital platforms. These key enablers may then be used to develop good strategies to enhance competitiveness and build the resilience of this sector against the disruptions brought on by the pandemic.

An attenuating, isotropic and heterogeneous uppermost inner core: evidence from global PKiKP-PKIKP amplitude ratio tomography

SUMMARY The Earth's inner core is solidifying from the liquid outer core, where convection currents power the geodynamo. Constraining properties of the inner core is fundamentally important, yet seismic models do not reconcile body wave and normal mode attenuation properties. Here, we analyse high signal-to-noise ratio core-refracted (PKIKP) and core-reflected (PKiKP) waves generated by earthquakes recorded globally between 1987 and 2021. These phases are excellent indicators of uppermost inner core (UIC) properties due to their low angular separation at the core–mantle boundary and similar ray paths. We analyse their amplitude ratios (ARs) and time delays (DTs) relative to synthetic waveforms and estimate the required attenuation perturbations in a linearized attenuation tomography. The UIC is cylindrically isotropic and heterogeneous in both seismic velocity and attenuation. Contrary to the paradigm that the inner core is seismically hemispherical, we find more complex patterns of attenuation that correlate with seismic velocities, according to both Akaike criterion and Student's t-test. The UIC beneath NE Asia is weakly attenuating and seismically slower, in contrast to the expected properties associated with the quasi-Eastern Hemisphere. Beneath South America, where the core is thought to grow fastest, AR values are more diverse, possibly reflecting interdendritic melt inclusions, and DTs show an E–W gradient. The UIC is seismically slow and weakly attenuating beneath the Atlantic, but strong anomalies emerge near West Africa. Attenuation slightly changes with depth conceivably implying an increase in melt degree or a change in inner core growth rate with time. These 3-D heterogeneities are inconsistent with simple models of core translation or lopsided growth, indicating that more intricate processes are needed to explain inner core structure and evolution.

The Components of Change in Population Growth Rates.

The demographic balance equation relates the population growth rate with crude rates of fertility, mortality, and net migration. All these rates refer to changes occurring between two time points, say, t and t + h. However, this fundamental balance equation overlooks the contribution of historical fertility, mortality, and migration in explaining these population counts. Because of this, the balance equation only partially explains a change in growth rate between time t and t + h as it does not include the contribution of historical population trends in shaping the population at time t. The overall population growth rate can also be expressed as the weighted average of age-specific growth rates. In this article, we develop a method to decompose the historical drivers of current population growth by recursively employing the variable-r method on the population's average age-specific growth rates. We illustrate our method by identifying the unique contributions of survival progress, migration change, and fertility decline for current population growth in Denmark, England and Wales, France, and the United States. Our results show that survival progress is mainly having an effect on population growth at older ages, although accounting for indirect historical effects illuminates additional contributions at younger ages. Migration is particularly important in Denmark and England and Wales. Finally, we find that across all populations studied, historical fertility decline plays the largest role in shaping recent reductions in population growth rates.

Antecedents and Consequences of Interest Rate Spread: Case of Pakistan

Interest rate spread plays a crucial role in the monetary policies of the government and has a substantial impact on the economy. This article examines the bank-specific determinants of interest rate spread which include capital adequacy ratio, non-performing loans, and overhead expenses. To analyze the impact of Interest Rate Spread (IRS) on the economy, specifically, change in GDP growth rate, change in the inflation rate, change in industrial growth rate, change in foreign exchange reserves, and change in the stock market index, while ROA, ROE, and NIM are used as profitability measures of the banking sector. Data from 2011-2020 is collected and analyzed through a linear regression model, which gives significant results as twenty-two out of twenty-four hypotheses are accepted. These results will help policymakers to better formulate monetary policies and will provide the basis for new insight into IRS.

Growth curve of early-weaned Hereford calves in a semidesert temperate zone (Patagonia, Argentina)

In semi desert environments, prone to droughts, beef cow performance can be improved by early weaning. This study aimed to evaluate the growth curve of early weaned calves in a semidesert temperate area such as Patagonia, Argentina, using a classical growth curve model. Hereford and crossbred (3/4 Hereford x 1/4 Aberdeen Angus) calves (n = 56), born in spring (September - November), from multiparous cows (4 to 8 years old), were weaned at 45–145 d of age, with 43–156 kg live weight and placed in a feedlot. After a period of adaptation, the calves were fed ad libitum with a diet of corn (48%), soybean expellers (12%) and alfalfa (40%), which was adjusted weekly for the previous week's intake. The animals were weighed weekly. The growth curve was defined by a Bayesian stepwise model selection process based on Richards’ growth curve. The resulting model is a Gompertz-like curve (near-zero shape parameter), in which females experience a change in growth rate at about 62.7 kg, from where their r increases from 0.0065 to 0.0121 becoming similar to that of males. The whole model had a high fit, with a generalized r2 of 0.8782. The average daily gain (ADG) was 0.804 kg/day for female calves and 0.934 kg/day for male calves. Female calves weighing less than 80 kg had an ADG of 0.672 kg/day, and those weighing more had an ADG of 0.847 kg/day. The current growth curve shows that it is possible to achieve high ADG in early weaned calves, confirming that early weaning is a viable alternative to make production systems more efficient in semi desert environments like Patagonia. Knowing the relationship between concentrate feeds and livestock prices, farmers will be able to decide whether early weaning is a profitable alternative or not is a profitable alternative. However, special care must be taken when weaning heifers that weigh less than 80 kg to achieve high ADG.

Investigation And Development Of Anti Polymicrobial Biofilm From Several Essential Oils: A Review

A biofilm is a group of microbes covered with extracellular polymeric substances (EPS) matrix and attached irreversibly to any surface. Biofilm can protect microbe, so microbe could resist the antimicrobial agent and spare from the host immune system. The development of biofilm could be spurred with the occurrence of serum and saliva. Biofilm developed along with increasing clinical infection, so that biofilm also acts as virulence and resistance factors. Furthermore, there are changes in phenotype such as growth rate and gene transcription change in free cell and planktonic cells. Biofilm is involved in many contagious diseases and resistance to various drugs, so it is essential to search and discover a new antibiofilm agent that could inhibit and eradicate biofilm formation. Some discovery a few years ago found that compound from the natural product has chemopreventive and antimicrobial activity in the modulation of biofilm formation. This review summarizes several current research studies related to infection of polymicrobial biofilm and searches for natural polymicrobial antibiofilm with a precise mechanism. The current antibiofilm agents listed here are promising candidates and could give a new approach to managing the infectious disease with polymicrobial biofilm.

Tropical methane emissions explain large fraction of recent changes in global atmospheric methane growth rate

Large variations in the growth of atmospheric methane, a prominent greenhouse gas, are driven by a diverse range of anthropogenic and natural emissions and by loss from oxidation by the hydroxyl radical. We used a decade-long dataset (2010–2019) of satellite observations of methane to show that tropical terrestrial emissions explain more than 80% of the observed changes in the global atmospheric methane growth rate over this period. Using correlative meteorological analyses, we show strong seasonal correlations (r = 0.6–0.8) between large-scale changes in sea surface temperature over the tropical oceans and regional variations in methane emissions (via changes in rainfall and temperature) over tropical South America and tropical Africa. Existing predictive skill for sea surface temperature variations could therefore be used to help forecast variations in global atmospheric methane.

Basics of surface reconstruction during selective area metalorganic chemical vapour-phase epitaxy of GaAs films in the stripe-type ultra-wide window

The evolution of the surface morphology and growth steps of the GaAs film during selective area epitaxy has been studied. It has been shown that during the selective area epitaxy three regions with different growth mode and the atomic-height step orientation can be formed. A correlation between the local misorientation and the specific features of these areas has been identified. The layer surface’ local misorientation angle causes the transition between growth modes. A simulation model of the change in the growth steps’ front in the window area is proposed. It is shown that the local rotation angle of the growth steps’ front is governed by the growth rate change across the window. It was experimentally and theoretically shown that a small change in the orientation of the growth steps in the central area of the window and a rotation of the front by nearly 90°for the outermost window areas are specific features due to the symmetric mask, whereas the size of the central area decreases sharply with increasing layer thickness.

Characterization of volumetric growth of intracranial meningiomas in Māori and Pasifika populations in New Zealand.

Māori and Pasifika populations in New Zealand have a higher incidence and prevalence of intracranial meningioma (IM). We sought to evaluate the volumetric growth rate of meningiomas under surveillance in these populations. From July 2002 to October 2020, 336 patients with a total of 408 IM underwent conservative management with serial radiological surveillance at Auckland City Hospital and met the criteria for the study. Inclusion criteria included: age >16 at diagnosis, ≥2 appropriate scans one or more years apart. Exclusion criteria included previous cranial irradiation, a diagnosis of Neurofibromatosis and prior treatment of meningioma. Demographic and clinical data were obtained from the electronic medical records. Imaging data were recorded from the first and last scans. We utilized open-source image processing software (3D Slicer) for semi-automated segmentation and volume calculation. Consistent with previous literature, we calculated the relative growth rate (RGR, %/year) and annual volume change (AVC, cm3 /year) over time. Four hundred and eight meningiomas were volumetrically characterized for a mean duration of 6.2 years. The Māori and Pasifika populations (n= 134/393) demonstrated a higher RGR (31.41 versus 14.33%/year) (P= 0.026) and AVC (2.05 versus 0.95 cm3 ) (P= 0.025) compared to the control population. They also presented at a younger age and had a higher rate of tumour multiplicity. Males represented only 17.6% of the cohort but exhibited a higher growth rate (AVC=2.52 cm3 /year) than females (AVC=0.99 cm3 /year) (P= 0034). Māori and Pasifika populations in New Zealand have a higher incidence and volumetric growth rate of IM compared to a control population. This warrants further clinical, histopathological and genomic analysis.

Population Dynamics of a Two Phages-One Host Infection System Using Escherichia coli Strain ECOR57 and Phages vB_EcoP_SU10 and vB_EcoD_SU57.

In this study, we looked at the population dynamics of a two phages-one host system using phages vB_EcoP_SU10 (SU10) and vB_EcoD_SU57 (SU57) and the bacteria Escherichia coli, strain ECOR57. Phage-specific growth curves were observed where infections by SU10 resulted in a moderate production of phages and infections by SU57 resulted in a fast and extensive production of phage progeny. Sequentially adding SU10 followed by SU57 did not produce a significant change in growth rates, whereas adding SU57 followed by SU10 resulted in a decrease in SU10 titer The efficiency of the plating assays showed that ECOR57 exhibited a resistance spectrum after infection by both the single and combined phages. Phage-resistant bacteria exhibited four different morphotypes (i.e., normal, slimy, edgy, and pointy). The normal and edgy morphotypes had a high frequency of developing resistance. Bacterial growth and biofilm assays indicated that the edgy and pointy morphotypes reached a stationary phase faster and produced more biofilm compared to the wild type. These findings suggest that the dynamic structure of phage–bacteria communities dictate resistance evolution and development. Understanding when and how resistances arise and phage(s)–hosts interactions could aid in the design of phage therapy treatments.

Ecological impact of changes in intrinsic growth rates of species at different trophic levels

Decreased and increased intrinsic growth rate and abundance of a single species can severely and negatively impact other species in the same food web. Here we compare the wider system effects of decreased and increased intrinsic growth rates of species occupying different trophic levels. Specifically, we derive the change in growth rate of a single (focal) species necessary to cause a 90% reduction in the abundance – a quasi‐extinction – of another species in model communities. We find that even relatively small changes, negative as well as positive, in the growth rate of the focal species can cause quasi‐extinctions of others. Furthermore, the magnitude of change needed to cause a quasi‐extinction depends on the trophic level of the perturbed species. The potential ecosystem impact of such ‘negative' and ‘positive' changes is largely unknown. We argue that such a targeted decrease or increase could be induced by human interference, such as hunting or harvesting, but also by an outbreak or fade‐out of an infectious disease. As ecosystems maintain many and diverse infectious agents, these results suggest that these agents may play an important role in the structure and balance of ecosystems.

Potential effect of tolvaptan on polycystic liver disease for patients with ADPKD meeting the Japanese criteria of tolvaptan use.

Polycystic liver disease (PLD) is a common extrarenal complication of autosomal dominant polycystic kidney disease (ADPKD), which causes compression-related syndrome and ultimately leads to liver dysfunction. Tolvaptan, a V2 receptor antagonist, is widely used to protect kidney function in ADPKD but its effect on PLD remains unknown. An observational cohort study was conducted to evaluate tolvaptan's effect on patients with PLD due to ADPKD. After screening 902 patients, we found the 107 ADPKD patients with PLD who met the criteria of tolvaptan use in Japan. Among them, tolvaptan was prescribed for 62 patients (tolvaptan group), while the other was defined as the non-tolvaptan group. Compared with the non-tolvaptan group, the tolvaptan group had larger height-adjusted total kidney volume (median 994(range 450-4152) mL/m, 513 (405-1928) mL/m, p = 0.01), lower albumin level (mean 3.9±SD 0.4 g/dL, 4.3±0.4g/dL, p<0.01), and higher serum creatinine level (1.2±0.4 mg/dL, 0.9±0.2 mg/dL, p<0.01). Although the median change in annual growth rate of total liver volume (TLV) was not statistically different between the tolvaptan group (-0.8 (-15.9, 16.7) %/year) and the non-tolvaptan group (1.7 (-15.6-18.7) %/year)(p = 0.52), 20 (43.5%) patients in the tolvaptan group experienced a decrease in the growth rate of TLV (responders). A multivariable logistic regression model adjusting for related variables showed that older age (odds ratio 1.15 [95% CI 1.01-1.32]) and a higher growth rate of TLV in the non-tolvaptan period (odds 1.45 95% CI 1.10-1.90) were significantly associated with responders. In conclusion, the change in annual growth rate of TLV in ADPKD patients taking tolvaptan was not statistically different compared with that in ADPKD patients without taking tolvaptan. However, tolvaptan may have the potential to suppress the growth rate of TLV in some PLD patients due to ADPKD, especially in older patients or those that are rapid progressors of PLD. Several limitations were included in this study, therefore well-designed prospective studies were required to confirm the effect of tolvaptan on PLD.

The metabolomics profile of growth rate in grazing beef cattle

This study aimed to determine the relationship between the metabolome and changes in growth rate (i.e., liveweight change, LWC) and molasses-lick block supplement intake (MLB) of grazing cattle. Weaner beef cattle were fed for 220 days with a sequence of feed types and blood samples, growth rate, and supplement intake were taken on five points in time. The relative abundance (RA) of plasma metabolites were determined using proton nuclear magnetic resonance (NMR). Sixty-four per cent of the metabolites identified were associated with LWC but only 26% with MLB intake (P < 0.05). Periods with faster growth rate showed high availability of amino acids (i.e., valine, leucine, isoleucine, phenylalanine and tyrosine), acetate, and 3-hydroxybutyrate. Periods with lower growth rate were associated with high RA of lipids, choline and acetate. The metabolic profile of individual animals during a period of compensatory growth (after periods of poor performance) showed that high-performing animals were characterised by lower RA of amino acids (i.e., valine, leucine, isoleucine, methylhistidine), creatinine, creatine, pyruvate, 3-hydroxybutyrate, and acetyl groups. It is speculated that high-performing animals have faster uptake of these metabolites from the bloodstream. Cattle growth rate over time was associated with their metabolome which could be used to ensure that the availability of certain metabolites promoting growth is tailored in feed supplements to improve production.

Safety and Efficacy of Burosumab in Pediatric Patients With X-Linked Hypophosphatemia: A Phase 3/4 Open-Label Trial.

ObjectiveBurosumab, an anti-fibroblast growth factor 23 antibody, was recently approved for the treatment of X-linked hypophosphatemia (XLH).We evaluated the safety and efficacy of burosumab in pediatric XLH patients.MethodsThis open-label, phase 3/4 trial of ≤ 124 weeks’ duration was conducted at 4 Japanese medical centers. Fifteen children aged 1 to 12 years with XLH were included. All had previously been treated with phosphorus or vitamin D. Subcutaneous burosumab was administered every 2 weeks, starting with 0.8 mg/kg, and adjusted based on serum phosphorus levels and any safety concerns (maximum 2 mg/kg). Safety assessments included the frequency of treatment-emergent adverse events (TEAEs). Efficacy of burosumab on biochemical markers, clinical markers of rickets, motor function, and growth was also evaluated.ResultsThe average treatment duration was 121.7 weeks. Frequently reported TEAEs were nasopharyngitis (46.7%), dental caries (40.0%), and influenza (33.3%). At baseline, patients had low serum phosphorus concentrations (2.6 ± 0.3 mg/dL) and low-to-normal 1,25-dihydroxyvitamin D concentrations (24.7 ± 12.7 pg/mL), which increased with burosumab treatment and were maintained during the study period. Alkaline phosphatase decreased continuously. At baseline, the mean ± SD total Thacher Rickets Severity Score (RSS) was 1.3 ± 1.2, and 4 patients (26.7%) had an RSS ≥ 2.0. Mean Radiographic Global Impression of Change and RSS tended to improve, particularly in patients with higher baseline RSS. There was a trend toward increased 6-minute walk test distance. No apparent changes in growth rate were observed.ConclusionBurosumab has a good safety profile and is effective in pediatric patients with XLH.

Past and future radial growth and water-use efficiency of Fagus sylvatica and Quercus robur in a long-term climate refugium

The low-latitudinal range margins of many temperate and boreal tree species consist of scattered populations that persist locally in climate refugia. Recent studies have shown that such populations can be remarkably resilient, yet their past resilience does not imply that they are immune to threats from future climate change. The functioning of refugial tree populations therefore needs to be better understood if we are to anticipate their prospects correctly. We performed a detailed study of tree radial growth and vigor in a long-term climate refugial population of beech (Fagus sylvatica), comparing the observed trends with those of co-occurring pedunculate oak (Quercus robur). Annual growth rates (basal area increment, BAI) for both species were similar to those observed in range-core populations, but natural lifespan was half that in the mountains. The master chronologies spanning 1870–2015 revealed 22% (Fagus) and 20% (Quercus) increases in BAI until the 1980s and a smaller decrease (−6% for Fagus, −9% for Quercus) since then. Stable carbon isotope measurements (δ13C) revealed no effect of cambial age and an increase in water-use efficiency (iWUE) from 1870–2015 of about 50% for Fagus and 20% for Quercus. The trend continued until 2015 in Fagus, whereas Quercus reached its maximum in the 1980s. A detailed analysis of the relationship between climate and annual growth based on a 118-year meteorological record revealed a major role of water availability in the current and previous year. We used the observed climatic relationships to model future growth trends until 2100 for the IPCC scenarios RCP4.5 and RCP8.5. Most projections revealed no change in current growth rates, suggesting that this climate refugium will be able to provide suitable conditions for the persistence of Fagus and Quercus over the coming decades even under warmer and drier regional climate conditions. Overall, our study provides valuable insight into the precise climatic and biological mechanisms enhancing the persistence of refugial tree populations under ongoing climate change.

Host plant limitation of butterflies in highly fragmented landscapes

Insect herbivores can be limited by host plants in two ways: density-dependent competition for food resources or density-independent search time limitation. Our understanding of density-dependent host plant limitation is relatively well developed and well integrated into conservation plans for at-risk insects. Search time limitation, a density-independent process, is much less well developed. Here, we explore both mechanisms using empirically based models of monarch butterfly population dynamics. These mechanisms differ fundamentally in their predictions: resource competition leads to matching of herbivore densities to host plant densities, and visible competition via consumption of host plants. Search time limitation leads to changes in population growth rate that can cause herbivore numbers to decline when host plant densities are constant. Search time limitation also implies that host plants can limit herbivores, even when many individual plants are uneaten. For monarch butterflies, our calculations suggest that many parts of North America have host plant densities below the threshold for search time limitation, which contrasts with the typical assumption of resource competition. More generally, incorporating search time limitation into conservation plans is important for reframing our understanding of how host plants limit insect herbivores in highly fragmented landscapes.