Tissue type matters: selective herbivory on different life history stages of an isomorphic alga

Selective grazing by herbivores can have large effects on the population dynamics and community structure of primary producers. However, the ecological impacts of within-species herbivore preference for tissues of different phases (e.g., ploidy levels) or reproductive status remain relatively poorly known, especially among algae and other species with free-living haploid (gametophyte) and diploid (sporophyte) phases. We tested for herbivore selectivity among tissue types of the isomorphic (identical haploid and diploid free-living stages) red alga Mazzaella flaccida. Laboratory feeding assays demonstrated that the snail Tegula funebralis exhibited more than a threefold preference for gametophyte reproductive tissue over other tissue types, due to morphological differences. In contrast, the urchin Strongylocentrotus purpuratus did not distinguish as clearly between gametophytes and sporophytes; but it did prefer sporophyte reproductive to nonreproductive tissue, due to differences in water-soluble chemicals. Field surveys of grazer damage on M. flaccida blades were consistent with these laboratory preferences, with more damage found on gametophytes than sporophytes and reproductive than nonreproductive tissues. Differential fecundity can contribute to a skew in relative frequencies of phases in the field, and our results suggest that differential grazing by snails may contribute to this pattern and thus play a role in algal population biology.     

Parthenogenesis,apogamy and apospory in Alaria crassifolia (Laminariales)

In cultures of Alaria crassifolia Kjellman, unfertilized eggs developed normally into haploid sporophytes which differentiated into a holdfast, stipe and blade with a midrib. The terminal cells of a male gametophyte grew apogamously into haploid sporophytes with narrow blades which lack the midrib. Further, diploid gametophytes were formed by apospory from vegetative cells of a diploid sporophyte. They were monoecious and their fertilized eggs developed into tetraploid sporophytes. Nuclear phases of the sporophytes and gametophytes concerned were confirmed by cytological observations.This work was supported by Grant No. 38803 from the Ministry of Education of Japan.     

Climate and predation dominate juvenile and adult recruitment in a turtle with temperature-dependent sex determination

Conditions experienced early in life can influence phenotypes in ecologically important ways, as exemplified by organisms with environmental sex determination. For organisms with temperature-dependent sex determination (TSD), variation in nest temperatures induces phenotypic variation that could impact population growth rates. In environments that vary over space and time, how does this variation influence key demographic parameters (cohort sex ratio and hatchling recruitment) in early life stages of populations exhibiting TSD? We leverage a 17-year data set on a population of painted turtles, Chrysemys picta, to investigate how spatial variation in nest vegetation cover and temporal variation in climate influence early life-history demography. We found that spatial variation in nest cover strongly influenced nest temperature and sex ratio, but was not correlated with clutch size, nest predation, total nest failure, or hatching success. Temporal variation in climate influenced percentage of total nest failure and cohort sex ratio, but not depredation rate, mean clutch size, or mean hatching success. Total hatchling recruitment in a year was influenced primarily by temporal variation in climate-independent factors, number of nests constructed, and depredation rate. Recruitment of female hatchlings was determined by stochastic variation in nest depredation and annual climate and also by the total nest production. Overall population demography depends more strongly on annual variation in climate and predation than it does on the intricacies of nest-specific biology. Finally, we demonstrate that recruitment of female hatchlings translates into recruitment of breeding females into the population, thus linking climate (and other) effects on early life stages to adult demographics.     

Life-history traits and the fate of translocated populations

Attempts to identify predictors and mechanisms of invasion success have been weakened by poor data quality, mostly because monitoring does not begin immediately after introduction events. To overcome this issue, we used data from conservation translocations of threatened bird species. We analyzed information on >1200 translocation events of >150 bird species to investigate how life-history traits affect population establishment measured based on rates of survival and reproduction. Species position along the slow–fast life-history continuum was a key predictor of translocation success. Species with fast-paced life histories were less likely to survive (over both short- and mid-term) and more likely to breed successfully than species with slow life histories. The temporal partitioning of reproductive effort (number of clutches per year) also affected the probability of successful reproduction. Our results illustrate how conservation-motivated reintroduction programs can provide proxies for the initial stages of the invasion process, enabling empirical tests of predictions from life-history theory and informing management.     

Leaf herbivory and decomposability in a Malaysian tropical rain forest

There is accumulating evidence that similar suites of plant traits may affect leaf palatability and leaf litter decomposability. However, the possible association between leaf herbivory and litter decomposition rates across species in species-diverse natural ecosystems such as tropical rain forests remains unexplored, despite its importance in estimating the herbivory effects on carbon and nutrient cycling of ecosystems. We found no strong association between leaf herbivory and litter decomposition rates across 40 tree species in a Malaysian tropical rain forest, even though the leaf and litter traits were tightly correlated. This is because the leaf and litter traits related to herbivory and decomposition rates in the field were inconsistent. Leaf toughness accounted for only a small part of the variation in the herbivory rate, whereas a number of litter traits (the leaf mass per area, lignin to nitrogen ratio, and condensed tannin concentration) accurately predicted the decomposition rate across species. These results suggest that herbivory rate across species may not be strongly related to single leaf traits, probably because plant-herbivore interactions in tropical rain forests are highly diverse; on the other hand, plant-decomposer interactions are less specific and can be governed by litter chemicals. We also investigated two factors, phylogeny and tree functional types, that could affect the relationship between herbivory and decomposition across species. Phylogenetic relatedness among the species did not affect the relationship between herbivory and decomposition. In contrast, when the plants were segregated according to their leaf emergence pattern, we found a significant positive relationship between herbivory and decomposition rates for continuous-leafing species. In these species, the condensed tannin to N ratios in leaves and litter were related to herbivory and decomposition rates, respectively. However, we did not observe a similar trend for synchronous-leafing species. These results suggest that the relationship between herbivory and decomposition may be more greatly affected by functional types than by phylogenetic relatedness among species. In conclusion, our results suggest that well-defended leaves are not necessarily less decomposable litter in a tropical rain forest community, implying that herbivory may not generate positive feedback for carbon and nutrient cycling in this type of ecosystem.     

Effects of nutrients, herbivory, and depth on the macroalgal community in the rocky sublittoral

We studied the interacting roles of nutrient availability and herbivory in determining the macroalgal community in a rocky littoral environment. We conducted a factorial field experiment where we manipulated nutrient levels and herbivory at two sublittoral depths and measured macroalgal colonization and the following young assemblage during the growing season. At the community level, grazing reduced algal colonization, though the effect varied with depth and its interaction with nutrient availability varied in time. In shallow water, the total density of macroalgae increased in response to nutrient enrichment, but the ability of grazers to reduce macroalgal density also increased with the nutrient enrichment, and thus, the community could not escape from the top-down control. In deep water, the algal density was lower, except in July when nutrient enrichment caused a very dense algal growth. Grazing at the greater depth, though effective, was generally of smaller magnitude, and in July it could not limit algal recruitment and growth. Species richness peaked at the intermediate nutrient level in deep but not in shallow water during most of the growing season. Grazing had no effect on diversity of the algal community at either depth and only a minor effect on species richness at the greater depth. Opportunistic and ephemeral algae benefited from the nutrient enrichment but were also grazed to very low densities. Slowly growing and/or perennial species colonized poorly in the nutrient enriched treatments, and depending on the species, either suffered or indirectly benefited from herbivory. For all species, effects of nutrients on colonization depended on depth; usually both nutrient and herbivory effects were more pronounced at the shallow depth. We conclude that grazers are able to reduce macroalgae over a large range of nutrient availabilities, up to 12-fold nutrient enrichment in the current experiment, and that the sublittoral depth gradient generates variation in the algal community control exerted by both herbivory and nutrient availability. Thus temporal and spatial variability in both top-down and bottom-up control and in their interaction, especially along the depth gradient, may be crucially important for producer diversity and for the successional dynamic in a rocky sublittoral environment.     

Effects of ocean temperature on the southern range limits of two understory kelps, <Emphasis Type="Italic">Pterygophora californica</Emphasis> and <Emphasis Type="Italic">Eisenia arborea</Emphasis>, at multiple life-stages

Environmental factors have long been shown to influence species distributions, with range limits often resulting from environmental stressors exceeding organism tolerances. However, these abiotic factors may differentially affect species with multiple life-history stages. Between September 2004 and January 2006, the roles of temperature and nutrient availability in explaining the southern distributions of two understory kelps, Pterygophora californica and Eisenia arborea (Phaeophyceae, Laminariales), were investigated along the coast of California, USA and the Baja California Peninsula, Mexico, by limiting either: (a) tissue nitrogen uptake and storage by adult sporophytes during periods of elevated temperature, and/or (b) production of embryonic sporophytes by microscopic gametophytes. Results suggest that while adult sporophytes of both species are tolerant of high temperatures and low nutrients, reproduction by their microscopic stages is not. Specifically, while E. arborea produced embryonic sporophytes at both 12 and 18°C, temperatures commonly observed throughout the southern portion of its range, P. californica produced sporophytes at 12 but not at 18°C. As a result, it appears that the southern distribution of P. californica, which ends in northern Baja California, Mexico, may be limited by temperature acting on its microscopic stages. In contrast, the ability of E. arborea’s microscopic and adult stages to tolerate elevated temperatures allows it to persist in the warmer southern waters of Baja California, as well as to the north along the California coast where both species co-occur.     

Long-term burning interacts with herbivory to slow decomposition

Fires can generate spatial variation in trophic interactions such as insect herbivory. If trophic interactions mediated by fire influence nutrient cycling, they could feed back on the more immediate consequences of fire on nutrient dynamics. Here we consider herbivore-induced effects on oak litter quality and decomposition within a long-term manipulation of fire frequency in central Minnesota, USA. We focused on bur oak (Quercus macrocarpa) trees, which are common across the fire frequency gradient and are often heavily infested with either lace bugs (Corythuca arcuata) or aphids (Hoplochaithropsus quercicola). We used targeted exclusion to test for herbivore-specific effects on litter chemistry and subsequent decomposition rates. Lace bug exclusion led to lower lignin concentrations in litterfall and subsequently accelerated decomposition. In contrast, aphid exclusion had no effect on litterfall chemistry or on decomposition rate, despite heavy infestation levels. Effects of lace bug herbivory on litterfall chemistry and decomposition were similar in burned and unburned areas. However, lace bug herbivory was much more common in burned than in unburned areas, whereas aphid herbivory was more common in unburned areas. These results suggest that frequent fires promote oak-herbivore interactions that decelerate decomposition. This effect should amplify other influences of fire that slow nitrogen cycling.     

Effects of ultraviolet radiation on different life cycle stages of the south Pacific kelps, Lessonia nigrescens and Lessonia trabeculata (Laminariales, Phaeophyceae)

The effects of exposure to ultraviolet radiation (UVR), 280–400 nm, in different life histories and development stages of the kelps, Lessonia nigrescens and L. trabeculata, collected in the south-east Pacific coast (30°S) were evaluated in the laboratory. Germination and viability (motile zoospores, settled spores), diameter of the primary cell of the gametophytes, percentage of female gametophytes, fertility and sporophytes production were measured after exposure to three radiation treatments (PAR; PAR + UVA; PAR + UVA + UVB). The effects of UVR in young sporophytes (diploid stage) were evaluated as changes in maximal quantum yield of chlorophyll fluorescence of photosystem II (PSII) (F _v/F _m). A significant decrease in all variables was observed for the treatment that included UVB (PAR + UVA + UVB) after 2 and 4 h of exposure, in relation to the control. The motile spores were more sensitive to UVR exposure compared to settled spores and gametophytes, suggesting that along with an increase in ontogenetic development; there is an increase in the tolerance to UVR. In addition, it was observed that early stages of the intertidal L. nigrescens were more tolerant to UVR compared to the subtidal L. trabeculata. These results allow initially to infer that UVR may be regarded as an important environmental factor influencing the upper limit of distribution of these species, mainly through its detrimental effects on the early stages of the life cycle.     

Nuclear events during early development in gametophytes of Macrocystis pyrifera,and the temporal effects of a marine contaminant

The time course of DNA synthesis in developing haploid gametophytes of the giant kelp Macrocystis pyrifera was determined, and the effects of arsenic (As) on the temporally distinct nuclear events, DNA synthesis and subsequent nuclear division/translocation, were investigated to establish which of these specific events may be disrupted by this contaminant. Experiments were carried out on material collected from kelp beds near Santa Barbara, California from 1993–1994. Timing of DNA synthesis was determined during development by use of the fluorochrome, DAPI (4,6-diamidino-2-phenylindole), and single-cell microspectrofluorometry. Zoospores, which result from meiosis, had already undergone two rounds of DNA synthesis at the time of release. The developing gametophytes underwent an additional two rounds of replication of DNA by 16 h of development, and following the first nuclear division/translocation, the gametophyte contained eight times the minimum DNA level throughout subsequent development. Both DNA synthesis and nuclear division/translocation, were found to be inhibited by As. Phosphate enrichment reduced the inhibitory effects of As on division/translocation of the nucleus, supporting the hypothesis that As interferes with phosphorylation. Gametophytes were more severely affected by As under light conditions, as opposed to dark, suggesting that photosynthesis may be more sensitive than dark metabolism.     

Distinctive types of leaf tissue damage influence nutrient supply to growing tissues within seagrass shoots

Herbivory is now recognized as an important structuring agent in seagrass meadows but the attack pattern and tissue damage of consumers are highly variable. Nutritional preferences of herbivores and/or easy access to resources may cause differences in biomass loss among tissues that damage the plant in functionally distinctive ways. The two main Mediterranean herbivores, the fish Sarpa salpa (L.) and the sea urchin Paracentrotus lividus (Lmk.), remove higher amounts of intermediate and external shoot leaves, respectively. To test whether this selective feeding can have different consequences on the allocation patterns of nutrient within plants, we simulated the effect of both herbivores by clipping external and intermediate leaves (plus unclipped controls) of Posidonia oceanica (L.) and we measured plant tolerance in terms of shoot growth and leaf nutrient supply to new tissue using isotopic markers. As expected, control treatments displayed high carbon and nutrient supply from external leaves (83% of the total ¹⁵N and 84% of the total ¹³C incorporated by the shoot). When subjected to clipping, the remaining leaves enhanced carbon and nitrogen supply compared with the control by 16% of N and 36% of C—in the intermediate clipping—and by over 100% of N and 200% of C—in the external clipping—to compensate for the nutrient lost. However, only in the case of fish herbivory (intermediate clipping), enhanced supply alone was able to fully compensate for the nutrient losses. In contrast, this mechanism is not completely effective when external leaves are clipped (urchin herbivory). Yet, the consequences of this nutrient loss under sea urchin herbivory are not apparent from the nutrient content of the new tissue, suggesting that there are other sources of nitrogen income (uptake or reallocation from rhizomes). Our study does not only confirm the tolerance of P. oceanica to herbivory, but also constitutes the first evidence of leaf-specific, compensatory nutrient supply in seagrasses.     

Do plant density, nutrient availability, and herbivore grazing interact to affect phlorotannin plasticity in the brown seaweed Ascophyllum nodosum

Plants have different strategies to cope with herbivory, including induction of chemical defences and compensatory growth. The most favourable strategy for an individual plant may depend on the density at which the plants are growing and on the availability of nutrients, but this has not been tested previously for marine plant–herbivore interactions. We investigated the separate and interactive effects of plant density, nutrient availability, and herbivore grazing on the phlorotannin (polyphenolic) production in the brown seaweed Ascophyllum nodosum. Seaweed plants grown at low or high densities were exposed either to nutrient enrichment, herbivorous littorinid gastropods (Littorina obtusata), or a combination of nutrients and herbivores in an outdoor mesocosm experiment for 2 weeks. Seaweeds grown at a low density tended to have higher tissue nitrogen content compared to plants grown at a high density when exposed to elevated nutrient levels, indicating that there was a density dependent competition for nitrogen. Herbivore grazing induced a higher phlorotannin content in plants grown under ambient, but not enriched, nutrient levels, indicting either that phlorotannin plasticity is more costly when nutrients are abundant or that plants responded to herbivory by compensatory growth. However, there were no significant interactive or main effects of plant density on the seaweed phlorotannin content. The results indicate that plants in both high and low densities induce chemical defence, and that eutrophication may have indirect effects on marine plant–herbivore interactions through alterations of plant chemical defence allocation.     

Effects of water motion on propagule release from algae with complex life histories

Reproductive marine algae with complex life histories may respond differently to water motion depending upon whether the spore-producing or gamete-producing phase is considered. Two such species, the kelp Alaria esculenta (L.) Greville (Phaeophyceae) and Ulva lactuca L. (Chlorophyta), were examined experimentally in the laboratory. The kelp was collected in April–June 2000 and U. lactuca was collected in July–August 2000, from four intertidal habitats at Schoodic Point, Maine, USA. Orbital shakers were used to generate water motion. Sporophylls of A. esculenta released more zoospores under shaken versus calm conditions, whereas fewer antheridia on the microscopic male gametophytes released sperm under shaken versus calm conditions when male and female gametophytes were placed together. However, antheridial sperm release was equivalent when male gametophytes were exposed to undiluted media from dense cultures of mature female gametophytes under shaken versus calm conditions. These data suggest that water motion inhibited sperm release by diluting the sperm-releasing pheromone produced by ripe eggs below a threshold required to cause sperm release. Water motion stimulated both gamete and zoospore release from U. lactuca. This is the first report in an alga of stimulation of gamete release by increased water motion, but it is notable that parthenogenesis occurs in Ulva spp.; thus, gametes may develop into gametophytes (1 N) or parthenosporophytes (2 N). This study demonstrates that water motion has strong effects upon algal reproduction, but that the effects may vary between species, possibly due to their different life histories.Communicated by J.P. Grassle, New Brunswick     

Eutrophication and Consumer Control of New England Salt Marsh Primary Productivity

Abstract:  Although primary productivity in salt marshes is thought to be controlled by physical forces, recent evidence suggests that human disturbances can drive a switch to consumer control in these ecologically valuable ecosystems. We tested the hypothesis that nitrogen enrichment can trigger consumer control in salt marshes in Narragansett Bay, Rhode Island, with (1) a field experiment in which we manipulated nutrient availability (with nutrient additions) and insect herbivory (with insecticide application), (2) a survey of 20 salt marshes that examined the relationship between marsh nutrient status and herbivore pressure, and (3) insect herbivore removal at high and low nutrient input sites to directly test the hypothesis that nutrient enrichment is increasing insect herbivory in these marshes. Experimental nitrogen eutrophication initially increased plant productivity but eventually led to reduced plant biomass due to insect herbivory, and our surveys revealed that marsh nitrogen supply was a good predictor of herbivore damage to plants. Insects had minimal impacts on primary productivity in pristine marshes, but suppressed primary productivity in eutrophic salt marshes by 50–75%. Thus, eutrophication is currently triggering consumer suppression of primary productivity in New England salt marshes and may ultimately jeopardize the ecological and societal services these systems provide.     

Reproductive biology of the red alga Polysiphonia lanosa (Ceramiales) in the Bay of Fundy, Canada

The purpose of this investigation was to establish reproductive phenology of the dioecious marine floridean red alga Polysiphonia lanosa (L.) Tandy. Specifically, the distribution and frequencies of male and female plants, timing of their sexual maturity, fecundity and success of fertilization were investigated. The presence of cystocarps was taken as an indication of syngamy. Populations of P. lanosa in the Bay of Fundy reproduce in spring, summer and autumn. Both male and female filaments were present in equal abundance at all sampling locations, grew in close proximity, and occurred with equal abundance at all elevations above chart datum. During the growing season most of the mature plants contained reproductive organs with apparently functional gametangia containing gametes the structure and behavior of which conformed to those reported in the literature for other species of the genus. Male and female plants of P. lanosa matured synchronously during late May to early July at all collecting sites. The ratio of spermatia to carpogonia calculated for the sampled population was high, 3000–4800 spermatia:1 carpogonium. At the end of the growing season (late October) the fertilization success was at its maximum of 50 to 90% and at its minimum in July at 24%. The three free-living life-history phases (females, males and tetrasporophytes) were abundant and occurred with equal frequency, indicating that a complete life cycle was common at the studied location. Received: 10 December 1996 / Accepted: 16 January 1997     

Crab herbivory regulates plant facilitative and competitive processes in Argentinean marshes

Interactions among plants have been hypothesized to be context dependent, shifting between facilitative and competitive in response to variation in physical and biological stresses. This hypothesis has been supported by studies of the importance of positive and negative interactions along abiotic stress gradients (e.g., salinity, desiccation), but few studies have tested how variation in biotic stresses can mediate the nature and strength of plant interactions. We examined the hypothesis that herbivory regulates the strength of competitive and facilitative interactions during succession in Argentinean marshes dominated by Spartina densiflora and Sarcocornia perennis. Spartina densiflora is preferred by the dominant herbivore in the system, the crab Chasmagnathus granulatus. We experimentally manipulated crab herbivory, plant structure, and shade, and we found that, when herbivory was low in the spring and summer, competitive interactions between plants were dominant, but in the fall, when herbivory was highest, facilitative interactions dominated, and Spartina densiflora survival was completely dependent upon association with Sarcocornia perennis. Moreover, experimental removal of Sarcocornia perennis across recently disturbed tidal flats revealed that, while Sarcocornia perennis positively affected small Spartina densiflora patches by decreasing herbivory, as patch size increases and they can withstand the impact of herbivory, competitive interactions predominated and Spartina densiflora ultimately outcompeted Sarcocornia perennis. These results show that herbivory can mediate the balance between facilitative and competitive processes in vascular plant communities and that the strength of consumer regulation of interactions can vary seasonally and with patch size.     

Lack of avoidance of phenolic-rich brown algae by tropical herbivorous fishes

High levels of polyphloroglucinol phenolics in marine brown algae are usually interpreted as a defensive response to herbivory. However, tropical brown algae generally contain very low levels of phenolics, even though herbivory in many tropical systems (e.g. coral reefs) is intense. This apparent paradox would be explained if polyphenolics did not deter tropical herbivores, in which case selection by herbivores for high levels of phenolics in tropical algae would be weak. To examine this hypothesis, in February 1989 we presented mixed assemblages of herbivorous fishes on the Great Barrier Reef with tropical, phenolic-poor brown algae (primarilySargassum spp.) and closely related (conspecifics in one instance) phenolic-rich temperate species. Different species of brown algae were eaten at very different rates, but these differences were not correlated with variation in the phenolic levels among the plants. TLC and NMR analyses showed no evidence of other, non-polar, metabolites in these algae, with the exception of the temperate speciesHomoeostrichus sinclairii. Thus, variation in non-polar metabolites also did not explain the differences in susceptibility to herbivores among these algae. We conclude that the herbivorous fishes studied here were not deterred by phenolic-rich algae, which suggests that levels of phenolics in many tropical algae may generally be low due to their ineffectiveness as defences. However, alternative explanations for the pattern are possible, and these are discussed.     

Population and leaf-level variation of iridoid glycosides in the invasive weed Verbascum thapsus L. (common mullein): implications for herbivory by generalist insects

Plant–insect interactions, which are strongly mediated by chemical defenses, have the potential to shape invasion dynamics. Despite this, few studies have quantified natural variation in key defensive compounds of invasive plant populations, or how those defenses relate to levels of herbivory. Here, we evaluated variation in the iridoid glycosides aucubin and catalpol in rosette plants of naturally occurring, introduced populations of the North American invader, Verbascum thapsus L. (common mullein; Scrophulariaceae). We examined two scales that are likely to structure interactions with insect herbivores—among populations and within plant tissues (i.e., between young and old leaves). We additionally estimated the severity of damage incurred at these scales due to insect chewing herbivores (predominantly grasshoppers and caterpillars), and evaluated the relationship between iridoid glycoside content and leaf damage. We found significant variation in iridoid glycoside concentrations among populations and between young and old leaves, with levels of herbivory strongly tracking leaf-level investment in defense. Specifically, across populations, young leaves were highly defended by iridoids (averaging 6.5× the concentration present in old leaves, and containing higher proportions of the potentially more toxic iridoid, catalpol) and suffered only minimal damage from generalist herbivores. In contrast, old leaves were significantly less defended and accordingly more substantially utilized. These findings reveal that quantitative variation in iridoid glycosides is a key feature explaining patterns of herbivory in an introduced plant. In particular, these data support the hypothesis that defenses limit the ability of generalists to feed on mullein’s well-defended young leaves, resulting in minimal losses of high-quality tissue, and increasing performance of this introduced species.     

Protection from Natural Enemies in Managing Rare Plant Species

Abstract: Natural enemies such as pathogens, herbivores, and seed predators can substantially limit the abundance of plants, including rare species. Vulnerability to particular enemies is likely to differ between life-history stages. We hypothesized that short-term protection of juvenile plants from herbivores can be used to increase population growth of rare species and thus improve the probability of long-term persistence. Using the federally listed (threatened) Pitcher's thistle ( Cirsium pitcheri ) as a model, we experimentally excluded insect herbivores from juvenile rosettes to evaluate the potential benefits of deliberate insect control as a tool for management of rare species. Herbivore effects varied spatially across the local environment. Excluding insects in portions of the habitat where herbivory was high had direct benefits, including a 53% decrease in juvenile plant mortality (60% to 7%) and a 10-fold increase in seed production of juveniles that matured and flowered. In other areas, where herbivore-induced juvenile mortality was relatively low, excluding insects either increased seed production of plants that flowered or had no major effect. Our data also suggest indirect benefits to the metapopulation via potential improvement in dispersal among patches. Temporal variation in growing conditions occurred between years, suggesting that multiple-year exclusions would be most effective. Our study suggests that small–scale manipulation of often inconspicuous interactions between rare plants and their natural enemies can be an effective, relatively low-cost tool for the management and restoration of rare plant species.     

Elytra color as a signal of chemical defense in the Asian ladybird beetle Harmonia axyridis

Carotenoid- and melanin-based colors are valuable indicators of quality in many vertebrates, but their signaling role in invertebrates remains relatively unexplored. The Asian ladybird beetle Harmonia axyridis is an ideal organism for studies of this nature because males and females exhibit highly variable red and black colors on their elytra and are chemically defended with an alkaloid (harmonine). We used digital photography to quantify elytra coloration and absorbance spectrophotometry and gas chromatography mass spectrometry analyses to quantify pigment and alkaloid concentrations, respectively, in wild-caught male and female H. axyridis. We predicted that extensive or intense coloration would be an aposematic signal of high-alkaloid stores. We found that carotenoid pigments largely controlled variation in red elytra coloration. There was no relationship between alkaloid content and either elytra redness or carotenoid pigment concentration in either sex. However, we found a positive correlation between the extent of elytra coloration and alkaloid content. Animals with proportionally more red (or less black) on the elytra were more alkaloid-rich; this relationship was particularly strong in females. We also found that females with lighter black spots had greater amounts of harmonine than those with darker spots. These results suggest that elytra color patterns have the potential to reveal information about chemical defensiveness to mates or predators. Prior studies in this species show that nonmelanic forms are typically less active and yet more sexually attractive than melanic forms, and both results may be explained by the fact that nonmelanics are better chemically defended.