Interference among cotton neighbours after differential reproductive damage

In indeterminate plant species, the rate of vegetative growth usually declines during the stage of active reproductive growth. Fruit shedding, as induced by insect herbivores, could counteract this decline. Due to the relative increase in vegetative growth, plants that have suffered reproductive damage could be better able to intercept light and acquire soil resources than undamaged plants. If so, plants with damaged neighbours might grow less than their counterparts with smaller, undamaged neighbours. This hypothesis was tested in high- and low-density cotton crops subjected to three treatments: (i) undamaged controls; (ii) uniformly damaged, in which all plants were damaged; (iii) non-uniformly damaged, in which every second plant was damaged. Damaged plants had their flowerbuds and young fruits manually removed at 85 days after sowing to simulate shedding as induced by Helicoverpa spp. (Lepidoptera) and mirid bugs (Hemiptera). As expected, damaged plants had greater leaf area and more vegetative dry matter than undamaged ones. This was most pronounced at high plant density. Neighbour status did not affect vegetative growth but it had a substantial, asymmetric effect on the reproductive growth of target plants. Damaged targets recovered to the level of undamaged controls in terms of total fruit number but had a large reduction in the mass of mature fruit due to the limited time available for recovery. The effect of neighbour status, if any, on the production of mature fruit in damaged targets was overridden by the limit imposed to recovery by the duration of the growing season. In contrast, neighbour status affected the production of mature fruit of undamaged targets: undamaged targets with damaged neighbours had 34% (low density) and 56% (high density) less mature fruit mass than their counterparts with undamaged neighbours. This was because (i) reproductive allocation and (ii) the proportion of total fruit that reached maturity in target plants declined with increasing neighbour interference. Most studies dealing with changes in competitive relationships among plants subjected to differential herbivory have shown how undamaged plants may benefit from herbivores that feed on their neighbours. This study shows that differential reproductive damage can cause the opposite effect, as undamaged plants may have a significant reduction in productivity due to the influence of neighbours whose vegetative growth was stimulated by the loss of reproductive organs. Received: 2 June 1996 / Accepted: 8 September 1996     

The potential for and constraints on the evolution of compensatory ability in Asclepias syriaca

To investigate the potential for and constraints on the evolution of compensatory ability, we performed a greenhouse experiment using Asclepias syriaca in which foliar damage and soil nutrient concentration were manipulated. Under low nutrient conditions, significant genetic variation was detected for allocation patterns and for compensatory ability. Furthermore, resource allocation to storage was positively, genetically correlated both with compensatory ability and biomass when damaged, the last two being positively, genetically correlated with each other. Thus, in the low nutrient environment, compensatory ability via resource allocation to storage provided greater biomass when damaged. A negative genetic correlation between compensatory ability and plant biomass when undamaged suggests that this mechanism entailed an allocation cost, which would constrain the evolution of greater compensatory ability when nutrients are limited. Under high nutrient conditions, neither compensatory ability nor allocation patterns predicted biomass when damaged, even though genetic variation in compensatory ability existed. Instead, plant biomass when undamaged predicted biomass when damaged. The differences in outcomes between the two nutrient treatments highlight the importance of considering the possible range of environmental conditions that a genotype may experience. Furthermore, traits that conferred compensatory ability did not necessarily contribute to biomass when damaged, demonstrating that it is critical to examine both compensatory ability and biomass when damaged to determine whether selection by herbivores can favor the evolution of increased compensation. Received: 2 April 1999 / Accepted: 21 September 1999     

Interactive effects of soil fertility and herbivory on Brassica nigra

Soil nutrient availability may affect both the amount of damage that plants receive from herbivores and the ability of plants to recover from herbivory, but these two factors are rarely considered together. In the experiment reported here, I examined how soil fertility influenced both the degree of defoliation and compensation for herbivory for Brassica nigra plants damaged by Pieris rapae caterpillars. Realistic levels of defoliation were obtained by placing caterpillars on potted host plants early in the life cycle and allowing them to feed until just before pupation on the designated plant. Percent defoliation was more than twice as great at low soil fertility compared to high (48.2% and 21.0%, respectively), even though plants grown at high soil fertility lost a greater absolute amount of leaf area (38.2 cm² and 22.1 cm², respectively). At both low and high soil fertility, total seed number and mean mass per seed of damaged plants were equivalent to those of undamaged plants. Thus soil fertility did not influence plant compensation in terms of maternal fitness. However, the pathways used to achieve compensation in seed production were different at low and high soil fertility. At low soil fertility, relative leaf growth rates (area added per inital area per day) of damaged plants were drastically reduced over the second week of caterpillar feeding. Damaged plants recovered the leaf area lost to herbivory in the two weeks following insect removal by increasing leaf relative growth rates above the levels seen for undamaged plants, but the replacement of leaf tissue lost to herbivory came at the expense of stem biomass. At high soil fertility, relative leaf growth rates of damaged plants were similar to those of undamaged plants both over the second week of caterpillar feeding and following caterpillar removal, and stem biomass was not affected by herbivory. These results suggest that higher levels of soil nutrients increased the ability of plants to stay ahead of their herbivores as they were being eaten. Because damaged plants at high soil fertility were able to maintain leaf growth rates to a greater extent than damaged plants at low soil fertility, they did not fall as far behind undamaged plants over the period of insect feeding and did not have as much catching up to do after feeding ended to compensate for herbivory.     

Population-level compensation after loss of vegetative buds: interactions among damaged and undamaged cotton neighbours

Population-level compensation occurs when herbivore attack on one individual allows another individual to grow more rapidly. This form of compensation was investigated in high and low density cotton crops subjected to three treatments: (i) undisturbed controls, (ii) uniformly damaged, in which all plants were damaged, and (iii) non-uniformly damaged, in which every second plant was damaged. Damaged plants had their vegetative buds manually removed to simulate damage by Helicoverpa spp. (Lepidoptera). Removal of vegetative buds did not reduce seed cotton production per unit ground area. In uniformly damaged crops, compensation was essentially the result of profuse branching after release of apical dominance and activation of axilary buds. In non-uniformly damaged crops, population level mechanisms acted that involved strong plant-plant interactions. At both plant densities, undamaged plants grown alongside damaged neighbours accumulated more root and shoot biomass and produced more seed cotton than undamaged plants in uniform crops. Different degrees of symmetry in the relationship between damaged and undamaged neighbours lead to different degrees of compensation, viz. seed cotton production of non-uniformly damaged crops ranged from 98 to 125% of that in controls. At high plant density, neighbour status also affected flowerbud initiation and/or retention. Changes in competitive relationships as well as early detection of and response to neighbour status were likely involved in these responses.     

Grazing tolerance of Gentianella amarella and other monocarpic herbs: why is tolerance highest at low damage levels?

Plants have adapted to compensate for the loss of vegetative biomass and reproductive potential caused by grazing. Shoot damage breaks down the correlative inhibition maintained by apical dominance. The consequent increased branching may lead to increased production of flowers and fruits in damaged plants, provided that enough resources, both in terms of meristems and nutrients, are available. In Gentianella amarella, the removal of the apex of the main stem (10% clipping) had no pronounced effect on branching and plant performance. In one of the two study populations, however, apically damaged plants produced more fruits than undamaged control plants. The plants also fully compensated for 50% removal of the main stem in terms of above-ground biomass, but their fruit production was reduced compared to control and apically damaged plants. After 75% clipping, fruit production was not significantly reduced compared to 50% clipping. Consequently, G. amarella showed highest tolerance in the presence of minor shoot damage. The pattern is qualitatively similar in some other monocarpic species (Gentianella campestris, Erysimum strictum and Rhinanthus minor). Multiple constraints as well as selective forces may shape these compensatory responses: (1) A lack of basal meristems may constrain tolerance of high damage levels. (2) Species with basal meristems may have a potential to tolerate major damage, but a shortage of resources or otherwise unfavourable growth conditions may constrain their compensatory ability. (3) It may be adaptive to have maximum tolerance of low and moderate damage levels if chemical defences reduce the risk of extensive shoot damage as well as the risk of repeated grazing. (4) The compensatory ability of monocarpic species may be affected by selective forces that favour fast vertical growth early in the season and unbranched architecture in undamaged conditions. Therefore, it is not the mere grazing history, but also other factors associated with growth conditions that are required to explain the variation in grazing tolerance.     

Towards an understanding of the mechanisms of tolerance: compensating for herbivore damage by enhancing a mutualism

Abstract.   1. Traditionally, losses in plant fitness or yield resulting from insect damage have been redressed by reducing pest populations using insecticides or biocontrol; these approaches rely on the untested assumption that reduced plant fitness or yield is caused by diminished resources available to damaged plants.
2. By experimentally manipulating pollination and damage levels independently, it is shown that pollination, as well as lack of resources, may be limiting to damaged plants in a model insect-pollinated crop, cantaloupe.
3. With enhanced pollination, damaged plants produce as much fruit as undamaged plants, even under high damage levels. In contrast, damaged plants without supplemental pollination produced significantly less fruit than undamaged plants.
4. This approach is unique in shifting the focus away from reducing pest populations and toward enhancing mutualistic interactions. It avoids risks posed by insecticides (which also kill pollinators) and by biocontrol agents, known threats to native species.
5. Determining the mechanism underlying compensation sheds light on recovery from insect damage in both natural and managed systems. These results have a bearing on managing native plant populations suffering from pollinator declines.
6. Finally, it may be predicted that resources could limit tolerance to herbivore damage in resource-poor or high competition environments, whereas pollination may limit tolerance when resource levels are high.     

叶片损害强度与基质营养水平对苦草补偿性生长的影响

通过室外双因子控制试验,研究了叶片损害强度与基质营养水平对沉水植物苦草补偿性生长的影响.结果表明：叶片损害与基质类型对苦草的累积生物量、生物量的分配（根叶比）及分株数均有显著影响.与未受损植物相比,强受损使苦草的累积生物量及无性分株数显著降低,根叶比明显升高,而弱受损与未受损处理之间没有明显差别.与营养贫瘠的岸泥相比,生长在肥力较高湖泥中的苦草的累积生物量较高,而根叶比与分株数较低;叶片损害与基质类型对苦草的相对生长率也有显著影响,受损使苦草的生长率明显提高,而两受损处理之间无显著差别.未受损与强受损时,湖泥中苦草的生长速率明显高于岸泥,弱受损时则相近.并初步探讨了水生植物受损后的补偿生长机理.     

Reproductive allocation and costs in gynodioecious Leucopogon melaleucoides (Ericaceae): implications for the evolution of gender dimorphism

In dioecious species, females typically allocate more resources to reproduction and incur greater costs of reproduction than males. In gynodioecious species, sex-based differences in reproductive allocation (RA) and costs have been less studied. Such knowledge, however, is relevant to address how females establish and increase in frequency in populations. We examine RA and reproductive costs by comparing fruit set, the proportion of biomass allocated to reproduction, and the responses of fruit set and vegetative growth to shoot defoliation in females and hermaphrodites in gynodioecious Leucopogon melaleucoides. Relative to hermaphrodites, females exhibited a two-fold fruit set advantage. Female fruit set increased proportionately with flower number, but hermaphrodite fruit set was reduced on plants with more flowers. Sex-based differences in allocation to other traits were small. Thus, female RA at flowering was similar to hermaphrodite RA, but was 1.4-fold greater at fruiting. Relative to controls, defoliation reduced fruit set and the percentage of shoots that produced new vegetative growth similarly in both sexes. However, females had a lower proportion of shoots with new growth overall. Further, defoliation on females reduced the dry mass of new growth by 44% compared with controls, whereas hermaphrodites were not affected. These results indicate a trade-off between reproduction and vegetative growth, and greater female costs of reproduction, particularly under resource-limiting conditions. In the absence of compensatory traits to offset higher female reproductive costs, such trade-offs have the potential to retard the spread of females in gynodioecious populations.     

种群密度与施肥对垂穗披碱草刈割后补偿作用的影响

 以甘南亚高山草甸常见牧草垂穗披碱草(Elymus nutans)为对象,通过考察种群密度、施肥与刈割处理等对植物生长和生殖的影响效应,比较了垂穗披碱草在5个密度及2个施肥实验处理条件下对4种刈割处理的补偿性反应特点。结果表明,在所有密度及施肥处理条件下,早期轻度刈割处理 (分蘖期刈割,留茬4 cm) 都有利于植物的补偿作用,后期重度处理 (拔节期刈割,留茬2 cm) 可显著降低植物的地上部分生物量及生殖部分干重 (穗重)。在不施肥情况下,刈割对垂穗披碱草的影响程度随种群密度而加大,在低密度处理中早期轻度刈割的植物发生了超补偿。可以认为,低密度种群中植物具有较多的分蘖是植物在刈割后表现出较高补偿能力的一个重要生物学原因。实验还发现,施肥可提高植物个体的分蘖能力和秆叶再生能力,因而总体上可增强植物的补偿能力,并且在中等密度条件下垂穗披碱草的补偿能力较强,尽管没有发生超补偿现象。不过,施肥主要是有利于植物地上营养器官的补偿,生殖器官的补偿程度较小一些。试验结果对科学管理人工草场具有一定的指导意义。     

Effects of apical damage on plant growth and male and female reproductive investments in <Emphasis Type="Italic">Ambrosia artemisiifolia</Emphasis>, a wind-pollinated plant

In wind-pollinated plants, apical damage may decrease male fitness by reducing height-dependent pollen dispersal distance, but may not affect female fitness because plant height is not always correlated with female fitness. We hypothesized that Ambrosia artemisiifolia responds to apical damage by (1) restoring plant height through compensatory growth from lateral buds, and/or (2) increasing the sex allocation to female function to compensate for the loss of male fitness. We tested these hypotheses by comparing a group of experimental removal of the apical meristem with three control groups and by field surveys on apically damaged plants. Experimental apical damage suppressed main stem growth, but promoted vertical secondary growth from lateral buds. These responses resulted in compensation of stem height in the apically damaged plants to the same height as one of three control groups. The numbers of male and female flowers and male racemes did not differ between damaged and undamaged plants, indicating that apically damaged plants did not change their sex allocation. Therefore, our results support our first hypothesis. The results of a field survey of naturalized populations also supported the first hypothesis in that plant height and the number of male racemes did not change in plants with apical damage. Consequently, our results suggest that A. artemisiifolia has a high ability of fitness compensation after apical damage by restoring height and male function. This ability may contribute to its invasiveness in disturbed habitats.     

刈割后两种不同体型植物的补偿式样对比研究

对比了两种不同体型植物燕麦(Avena sativa)和油菜(Brassica campestris)在不同施肥水平下的刈割反应特点。结果表明:对于燕麦而言,在不施肥条件下,3个时期的轻度刈割处理与对照相比,其生物量、总生物量、果重、果数等都有增加,但只有某些指标出现超补偿;在施肥条件下,各种刈割处理后均没有发生超补偿。并且无论施肥与否,分蘖期与拔节期的补偿指数均高于抽穗期的补偿指数。可以认为,不施肥条件下营养期轻度刈割处理较有利于燕麦的补偿生长。对于油菜而言,花蕾期轻度刈割处理后植物补偿指数最大,且施肥条件下的补偿指数高于不施肥条件下的补偿指数。比较两种植物在不同资源下补偿反应的特点,可认为因休眠芽位置及其活动方式不同而所造成的体型差异对植物的补偿反应式样有很大影响。     

新疆郁金香营养生长、个体大小和开花次序对繁殖分配的影响

植物有性繁殖与资源分配的关系研究对于揭示植物生活史特征及繁育系统进化具有重要意义。新疆郁金香(Tulipa sinkiangensis)是新疆天山北坡荒漠带特有的一种多年生早春短命植物。在自然生境中,该物种仅以有性繁殖产生后代,每株能产生1-8朵花,且不同植株上的花数及果实数以及花序不同位置上的花与果实大小明显不同。本文通过对新疆郁金香有性繁殖与营养生长及植株大小的关系以及花序中不同位置花及果实间的资源分配研究,旨在揭示营养生长、个体大小及开花次序对其繁殖分配的影响。结果表明:在开花和果实成熟阶段,新疆郁金香植株分配给营养器官(鳞茎和地上营养器官)与繁殖器官的资源间均存在极显著的负相关关系(P<0.01),说明其植株的营养生长与生殖生长间存在权衡关系。多花是新疆郁金香的一个稳定性状,其植株上花数目、花生物量、果实生物量和种子数量与植株生物量间均呈极显著的正相关关系(P<0.01),说明新疆郁金香植株的繁殖分配存在大小依赖性。在具2-5朵花的新疆郁金香植株中,花序内各花的生物量、花粉数和胚珠数、结实率、果实生物量、结籽数、结籽率及种子百粒重按其开花顺序依次递减,说明花序内各花和果实的资源分配符合资源竞争假说。植株通过减少晚发育的花或果实获得的资源来保障早发育的花或果实获得较多的资源,从而达到繁殖成功。     

Defoliation of the annual herb Abutilon theophrasti: mechanisms underlying reproductive compensation

A number of studies have shown that under some conditions plants may fully or partially compensate for leaf tissue loss; however, the mechanisms underlying compensatory responses are not well understood. Previous work demonstrated that the annual herb Abutilon theophrasti fully compensated for 75% defoliation, but only when grown in the absence of stem competition. We examined potential mechanisms of compensatory response and how they are influenced by resource limitation (i.e., competition for light). Full compensation for these annual plants was defined as equal final reproductive output in defoliated and control plants. In the current study we observed substantial compensation in defoliated plants growing at low density, despite losing 75% of leaf area prior to the onset of flowering. Plant responses associated with compensation included (1) increased reproductive efficiency, which may in turn may have resulted from increased canopy light penetration and transient increases in leaf-level photosynthetic rates; (2) greater allocation to reproduction (RA); (3) changes in biomass allocation from roots to shoots; (4) lower leaf longevity, and (5) increased percent fruit set. Although some of these responses were also observed in defoliated plants grown at high density, the inability of high-density plants to compensate appeared to result from competition for light; these plants delayed reproduction and continued to produce new leaves late in the growing season after low-density, defoliated plants had shifted allocation of resources to reproduction. Received: 20 June 1996 / Accepted: 12 February 1997     

From over to undercompensation: Variable responses to herbivory during ontogeny of a Neotropical monocarpic plant

Empirical and theoretical work has suggested that plants can change their compensatory responses to herbivory as they develop. However, such a relationship is likely to be more complex than previously thought since the amount and type of damage a plant receives can also change as the plant develops. Here, we determined the survival, growth, and reproductive output of plants (Actinocephalus polyanthus) from different ontogenetic stages that received variable levels of natural or simulated herbivore damage. Juvenile plants and non‐reproductive adults in which leaves were damaged showed full vegetative compensation, whereas pre‐reproductive plants were not able to replace the lost leaves. However, these same pre‐reproductive plants produced more inflorescences and thus more seeds and seedlings than control plants. In contrast, damage to vegetative and/or reproductive structures during the reproductive phase resulted in a negative effect on seed and seedling production. Herbivory effects on plant survival, growth, and reproduction during the vegetative and pre‐reproductive phases were independent of the amount of damage. However, during reproduction, the magnitude of these effects was strongly influenced by the amount of damage and the reproductive stage of the plant at the time of the damage. In short, our results demonstrate that the survival, growth, and reproductive responses to herbivory of A. polyanthus can be dependent on the timing and/or intensity of damage. The reproductive response of A. polyanthus to our simulated herbivory treatments during the pre‐reproductive phase represents an example of overcompensation. Furthermore, it indicates that vegetative regrowth is not necessarily a driving factor for tolerance.     

Effects of fruit thinning on fruit and seed features of <Emphasis Type="Italic">Cistus ladanifer</Emphasis>

Fruit and seed features are the result of reproductive allocation decisions which ultimately depend on both plant availability of resources and total number of developing fruits. In this study, we manipulated fruit load in Cistus ladanifer plants by removing 0, 25 or 75% of developing fruits. Fruit features (total fruit weight, fruit-wall weight, total seed weight per fruit and seed number per fruit) were unaffected by fruit thinning, nevertheless mean seed weight increased in treated plants independently of thinning intensity. This reduced compensation was unrelated to plant size and had no consequences on fruit predation by insects. From these results it could be suggested that not only availability of resources but also morphological constraints could affect seed size in Cistus ladanifer. On the other hand, this change in seed weight could have important consequences since in this species heavy seeds perform better after fire events but light ones are advantageous in between fire recruitments.     

Consequences of preformation for dynamic resource allocation by a carnivorous herb,Pinguicula vulgaris (Lentibulariaceae)

When resource availability changes frequently and unpredictably, natural selection favors flexible resource allocation; however, such versatility may be compromised in perennial plants that differentiate leaves or flowers a year in advance of their development (preformation). We investigated resource allocation by the carnivorous perennial Pinguicula vulgaris to determine whether increased resource availability changes within-season allocation to growth, vegetative propagation, and reproduction. In response to resource supplementation (feeding with fruit flies), plants attained a mass 60% greater than that of unfed plants after a single growing season. Feeding also enhanced vegetative propagation, which is closely associated with growth, without modifying relations between these two vegetative functions. In contrast, feeding did not alter the size of vegetative rosettes or the within-season incidence of either flowering or fruiting. This lack of immediate responses occurred because floral and leaf primordia differentiated up to 10 mo before resource supplementation and flower development. However, enhanced resource status likely affected future reproduction indirectly through resource effects on plant size. Large plants produced more floral primordia and between-year changes in fruiting status corresponded to changes in plant size. These results illustrate that preformation can delay responses to enhanced resources by perennial plants.     

Variation in grazing tolerance among three tallgrass prairie plant species

Three tallgrass prairie plant species, two common perennial forbs (Artemisia ludoviciana and Aster ericoides [Asteraceae]) and a dominant C(4) perennial grass (Sorghastrum nutans) were studied under field and greenhouse conditions to evaluate interspecific variation in grazing tolerance (compensatory growth capacity). Adaptation to ungulate grazing was also assessed by comparing defoliation responses of plants from populations with a 25-yr history of no grazing or moderate ungulate grazing. Under field conditions, all three species showed significant reductions in shoot relative growth rates (RGR), biomass, and reproduction with defoliation. In the two forbs, clipping resulted in negative shoot RGR and reductions in both number and length of shoot branches per ramet. Sorghastrum nutans maintained positive RGR under defoliation due to a compensatory increase in leaf production. Defoliation reduced rhizome production in A. ericoides and S. nutans, but not in A. ludoviciana. Clipping significantly reduced sexual reproductive allocation in all three species, although S. nutans showed a smaller reduction than the forbs. All three species showed similar responses to defoliation in burned and unburned sites. Under greenhouse conditions, a similar clipping regimen resulted in smaller reductions in growth and reproduction than those observed in the field. For all three species, the grazing tolerance indices calculated under natural field conditions were significantly lower than those estimated from greenhouse-grown plants, and the interspecific patterns of grazing tolerance were different. Aster ericoides exhibited the highest overall defoliation tolerance under greenhouse conditions, followed by S. nutans. Artemisia ludoviciana, the only study species that is typically not grazed by ungulates in the field, showed the lowest grazing tolerance. In the field experiment S. nutans showed the highest grazing tolerance and the two forbs had similar low tolerance indices. These patterns indicate that, despite high compensatory growth potential, limited resource availability and competition in the field significantly reduce the degree of compensation and alter interspecific differences in grazing tolerance among prairie plants. In all three species, defoliation suppressed sexual reproduction more than growth or vegetative reproduction. Significant interactions between plant responses to defoliation and site of origin (historically grazed or ungrazed sites) for some response variables (root/shoot ratios, rhizome bud initiation, and reproductive allocation) indicated some degree of population differentiation and genetic adaptation in response to a relatively short history of ungulate grazing pressure. The results of this study indicate that patterns of grazing tolerance in tallgrass prairie are both genetically based and also environmentally dependent.     

Seasonal Allocation and Efficiency Patterns of Biomass and Resources in the Perennial Geophyte Sparaxis grandiflora Subspecies fimbriata (Iridaceae) in Lowland Coastal Fynbos, South Africa

The seasonal allocation and efficiency of biomass and resources(starch, soluble carbohydrates, N, P, K, Ca, Mg, Na, Zn, Fe,Mn and Cu) within and between the constituent plant parts ofSparaxis grandiflora subspecies fimbriata , a deciduous, synanthousgeophyte, are described. The sequential production of roots,leaves and a new daughter corm, with fruit production phasedin during the development of the daughter corm, results in continualtransfer of resources when the plant is not dormant. The newdaughter corm serves as the major sink for the allocation ofdry matter and resources during the vegetative, reproductiveand senescent periods. The parent corm is the major source ofresources in the early stages of the vegetative period. Theamount of resources allocated to the reproductive structureswas comparatively low when compared with that allocated to vegetativeplant parts. The corms have highly flexible storage capacitiesfor a variety of nutrients, particularly the better conservednutrients such as nitrogen, phosphorus, potassium, and carbohydrates.The dynamic patterns for the majority of the resources revealedhigh allocation when metabolic activity was also highest. Efficientrecovery or recycling of important resources from senescingorgans results in a similar or greater allocation to the daughtercorm than the amount that was present in the parent corm ofthe previous growth season. This is seen as an advantage tothese plants that grow in a seasonal environment where soilsare of low nutrient status.Copyright 1994, 1999 Academic Press Dry mass, efficiency, phenophase, resource allocation, Sparaxis grandiflora, fynbos     

Effects of foliar herbivory by insects on the fitness of Raphanus raphanistrum: damage can increase male fitness

Generally, effects of herbivory on plant fitness have been measured in terms of female reproductive success (seed production). However, male plant fitness, defined as the number of seeds sired by pollen, contributes half of the genes to the next generation and is therefore crucial to the evolution of natural plant populations. This is the first study to examine effects of insect herbivory on both male and female plant reproductive success. Through controlled field and greenhouse experiments and genetic paternity analysis, we found that foliar damage by insects caused a range of responses by plants. In one environment, damaged plants had greater success as male parents than undamaged plants. Neither effects on pollen competitive ability nor pollinator visitation patterns could explain the greater siring success of these damaged plants. Success of damaged plants as male parents appeared to be due primarily to changes in allocation to flowers versus seeds after damage. Damaged plants produced more flowers early in the season, but not more seeds, than undamaged plants. Based on total seed production, male fitness measures from the first third of the season, and flower production, we estimated that damaged and undamaged plants had equal total reproductive success at the end of the season in this environment. In a second, richer environment, damaged and undamaged plants had equal male and female plant fitness, and no traits differed significantly between the treatments. Equal total reproductive success may not be ecologically or evolutionarily equivalent if it is achieved differentially through male versus female fitness. Genes from damaged plants dispersed through pollen may escape attack from herbivores, if such attack is correlated spatially from year to year.     

Sex allocation and reproductive success in the andromonoecious perennial Solanum carolinense (Solanaceae). I. Female

Relative allocation of resources to growth vs. reproduction has long been known to be an important determinant of reproductive success. The importance of variation in allocation to different structures within reproductive allocation is somewhat less clear. This study was designed to elucidate the importance of allocation to vegetative vs. reproductive functions, and allocation within reproductive functions (sex allocation), to realized female success in an andromonoecious plant, Solanum carolinense. Allocation measurements were taken on plants in experimental arrays exposed to natural pollination conditions. These measurements included total flower number, the proportion of flowers that were male, flower size, and vegetative size. Flower number explained the majority of the variation among individuals in their success-that is, there was strong selection for increased flower production. There was also selection to decrease the proportion of flowers that were male, but neither flower size nor vegetative size (a measure of overall resource availability) were direct determinants of female success. After Bonferroni corrections for multiple comparisons, most phenotypic correlations among the traits measured were nonsignificant. Thus, in this andromonoecious species there is not a strong relationship between resource availability (vegetative size) and female success, and female success is instead determined by the relative production of the two different flower types.