Genetically based polymorphisms in morphology and life history associated with putative host races of the water lily leaf beetle,Galerucella nymphaeae

A host race is a population that is partially reproductively isolated from other conspecific populations as a direct consequence of adaptation to a specific host. The initial step in host race formation is the establishment of genetically based polymorphisms in, for example, morphology, preference, or performance. In this study we investigated whether polymorphisms observed in Galerucella nymphaeae have a genetic component. Galerucella nymphaeae, the water lily leaf beetle, is a herbivore which feeds and oviposits on the plant hosts Nuphar lutea and Nymphaea alba (both Nymphaeaceae) and Rumex hydrolapathum and Polygonum amphibium (both Polygonaceae). A full reciprocal crossing scheme (16 crosses, each replicated 10 times) and subsequent transplantation of 1,001 egg clutches revealed a genetic basis for differences in body length and mandibular width. The heritability value of these traits, based on midparent-offspring regression, ranged between 0.53 and 0.83 for the different diets. Offspring from Nymphaeaceae parents were on average 12% larger and had on average 18% larger mandibles than offspring from Polygonaceae parents. Furthermore, highly significant correlations were found between feeding preference of the offspring and the feeding preference of their parents. Finally, two fitness components were measured: development time and survival. Development time was influenced by diet, survival both by cross type and diet, the latter of which suggest adaptation of the beetles. This suggestion is strengthened by a highly significant cross x diet interaction effect for development time as well as for survival, which is generally believed to indicate local adaptation. Although no absolute genetic incompatibility among putative host races was observed, survival of the between-host family offspring, on each diet separately, was lower than the survival of the within-host family offspring on that particular host. Survival of offspring of two Nymphaeaceae parents was about two times higher on Nymphaeaceae than on Polygonaceae, whereas survival of offspring of two Polygonaceae parents was 11 times higher on Polygonaceae than on Nymphaeaceae (based on untransformed data). Based on these results, we conclude that genetically determined polymorphisms in morphology and feeding preference exist in G. nymphaeae, resulting in differential performance. Furthermore, in each diet separately, offspring of between-host family crosses were less fit than offspring of within-host family crosses. These results support the hypothesis that within this species two host races can be distinguished.     

菱角萤叶甲不同地理种群及近缘种rDNA-ITS1基因序列初步分析

通过对我国菱角萤叶甲Galerucella birmanica Jacoby 6个地理种群和褐背小萤叶甲Galerucella grisescens Joannis扬州种群的核糖体DNA第1内转录间隔区（rDNA-ITS1）的测序,并调用GenBank中该属其它4种昆虫的同源序列,运用软件DNAStar的MegAlign程序对小萤叶甲属种间、同种不同地理种群之间的ITS1序列的遗传分歧及相似性进行了分析,运用Mega3.0软件建立系统发育关系.序列分析结果表明,rDNA-ITS1基因在小萤叶甲属昆虫中进化速度较快,种下具有一定的差异,种间差异明显.该基因适合小萤叶甲属种间和种下的分类鉴定研究.进化树显示,菱角萤叶甲泰安种群和扬州种群形成一个分支,益阳种群和新余种群形成一个分支,苏州种群和上海青浦种群形成一个分支,这一现象说明6个地理种群的菱角萤叶甲分化与寄主和地理距离之间具有较高的相关性.     

The effect of the water-lily beetle, Galerucella nymphaeae, on leaf production and leaf longevity of the yellow water-lily, Nuphar lutea

SUMMARY. 1. The effect of the water-lily beetle, Galerucella (= Pyrrhalta ) nymphaeae (L.), (Coleoptera, Chrysomelidae), on the leaf production and leaf longevity of the yellow water-lily, Nuphar lutea (= N. luteum ) (L.) Sibth. & Sm., was studied experimentally in southern Finland during one growth season.
2. Twelve cages, each containing a single rosette of the water-lily, were established in the lake during May. Two treatments were randomly applied to cages: (i) control (herbivory not allowed), and (ii) fifty beetles added at the beginning of the season. Leaves were marked individually and the production of new leaves was followed until October.
3. In both treatments the production of floating leaves continued until the end of August but declined towards the end of summer. Herbivory did not affect the number of leaves produced, i.e. the plants did not compensate for the loss of leaves.
4. Leaf longevity was reduced dramatically (up to —60%) when herbivores were present. Leaves that emerged during the most intense period of larval growth had a life-span one-third of that of the control group.     

Ecological modulation of environmental stress: interactions between ultraviolet radiation, epibiotic snail embryos, plants and herbivores

1. The distribution of egg masses of the freshwater snails Lymnaea stagnalis and Planorbarius corneus on the undersides of water lily leaves (e.g. Nuphar lutea) is related to the prevalence of the leaf-mining beetle Galerucella nymphaeae. 2. When given the choice, Planorbarius significantly avoids leaves that were infested by the mining beetle. Conversely, Lymnaea did not discriminate against mined leaves. 3. Intact Nuphar leaves block over 95% of incident ultraviolet radiation. Yet, ultraviolet transmission reaches almost 100% under beetle mining scars. These are several times wider than snail embryos. 4. When exposed to natural sunlight, Lymnaea embryos proved to be resistant to ambient ultraviolet, while Planorbarius embryos were rapidly killed. Thus, one selective advantage of Planorbarius discrimination against mined leaves when depositing its eggs could be the avoidance of ultraviolet radiation passing through mining scars. 5. Other mining-related modifications of the leaves, reduced area, decreased longevity, altered aufwuchs (i.e. biofilm and epibionts) are discussed but seem less relevant for the oviposition preference of Planorbarius. 6. The discriminatory behaviour of this snail species was triggered by water-borne cues emitted by the damaged leaf, not by the eggs or larvae of the beetle. 7. This study illustrates how environmental stress on a given species, ultraviolet radiation in this case, can be ecologically buffered (shading by Nuphar) or enhanced (reduction of Nuphar shading through beetle mining) by associated species. It highlights how the impact of a given stress depends on the identity of the target species as well as on the identity and role of other species in the community.     

Host race formation in the meadowsweet and strawberry feeding leaf beetle Galerucella tenella

We investigated host race formation in Galerucella tenella, a leaf beetle which feeds preferentially on meadowsweet (Rosaceae) in its natural habitats, but has become an important pest on strawberry (Rosaceae) in agricultural areas. Beetles from two isolated sites (Skeppsvik in Sweden and Solf in Finland) were compared with respect to preference and performance. At Skeppsvik the beetles were found feeding on meadowsweet, while at Solf large populations only develop in strawberry plantations, despite the presence of meadowsweet.In reciprocal field transplantations and laboratory bioassays, beetles from both sites discriminated against their foreign host, using their natal plant to a significantly higher degree for both egg laying and feeding, but with one interesting exception, namely that beetles from Solf increased their use of and even preferred meadowsweet for feeding in the laboratory. This increased use of meadowsweet by adult Solf beetles in the laboratory (without conspecific competitors) may be attributed to a density-dependent strategy, whereby mothers avoid pre-emptying the nutritional resources of the plants that will host their offspring in cases where no competitors are present.Larval fitness did not differ significantly between host plants, although larval survival of Solf beetles was halved when reared on their non-natal host plant (meadowsweet). Although beetles from both sites preferred to oviposit on their local host plant, our results provide little evidence that this presumed adaptation has to do with the nutritional quality of the plants involved. Instead, we suggest that other factors associated with the plants, such as enemy-free space and resistance to drought may be more important selective agents, shaping host preference in the field.     

Habitat selection of three chrysomelid species associated with Rumex spp.

Summary Habitat selection of three chrysomelid beetles feeding on the Rumex plants was studied in relation to the ecological requirements of the three species and the habitat characteristics arising in their unstable and often unpredictable environment. The different ecological requirements and bionomic characteristics of the three chrysomelids were associated not only with their differing degrees of feeding specialization; they also influenced habitat selection. For example, the small body size and lower food demands of Mantura clavareaui, which is a feeding specialist, allowed it to exploit any habitat, irrespective of habitat size and duration. The other specialist, Gastrophysa atrocyanea, selected larger habitats because of the relatively brief lifespan of its adults after overwintering, its reduced mortality, and greater food demand. On the other hand, Galerucella vittaticollis, which is a multivoltine, general feeder, selected the habitat that lasted longer, rather than one that was larger. This species' life cycle is not synchronized with Rumex phenology, but its adults are long-lived and it has a flexible life cycle. The different patterns in habitat selection among these three chrysomelids prevented serious overlapping of their habitats; thus, the habitat overlapping of 2 or 3 species was 34.62%, that of all 3 species 3.85%. Most of the habitats utilized by Gastrophysa, however, overlapped those of the other two species, because Gastrophysa's habitat utilization range was the narrowest of the three. In Mantura, the degree of overlap with the other two species was lowest because this beetle had the broadest range of habitat utilization. On the other hand, Galerucella adjusted the temporal, rather than the spatial coordinates of its habitat usage when it occupied habitats where the other two specialists were also present. Galerucella, unlike the other two species, is multivoltine. Consequently, it was able to coexist in habitats occupied by the others by exploiting the host plants at times when the other species were numerically few, or even absent. No direct interspecific competition among adults of the three species was observed. Their different patterns of habitat selection created by their different responses to available food allowed them to coexist on Rumex without direct competition.     

北热带喀斯特森林木本植物花性状及其生境分异

植物花性状的多样化是植物长期进化及自然选择的结果, 不同植物种间花性状的变异与生境存在一定的相关性。北热带喀斯特季节性雨林具有生境异质性强、群落结构复杂、特有成分丰富等特点, 分析该森林植物性状的变化特征及其与生境的关联性, 有助于理解物种共存、协同进化过程和对生境的适应, 可为阐明喀斯特植物的生态适应性、理解生物多样性维持机理提供依据。本研究在弄岗15 ha森林动态监测样地木本植物开花相对集中的时间段进行, 记录并分析了21个物种花性状的变化。根据物种空间分布及其与生境的关联特性, 将21个物种分成偏好谷底、山坡、山顶的3种类型, 分析了这3种类型植物的花性状差异; 另外又根据花性状对21个物种进行聚类分析, 探讨了聚类分组结果和根据偏好生境分组结果的异同。结果表明: 花大小、花色鲜艳度均与物种优势度存在显著的负相关关系, 花小而不鲜艳的物种在群落中更有优势, 表现出更好的适应性; 不同偏好生境的植物花色明度有显著差异, 其他的花性状差异不显著; 聚类分组与根据偏好生境的分组有较好的一致性, 反映出物种的花性状变化响应了生境的变化。综上结果, 我们认为北热带喀斯特季节性雨林植物花性状与物种的优势度及生境条件有密切联系, 在该区域中生境对花性状的影响可能比传粉者更为深刻。     

Shading enhances the quality of willow leaves to leaf beetles – but does it matter?

Plant shading is commonly recognised as a factor, which increases susceptibility of plants to attack by herbivorous insects. In this study we experimentally investigated the effect of host plant shading on two willow-feeding leaf beetles, Galerucella lineola feeding upon Salix phylicifolia and Phratora vitellinae feeding upon Salix myrsinifolia . Both beetle species were more abundant on potted willows growing in open habitats than on the same clones placed under the shade of trees. However, in the laboratory the food preference by adults and larval performance showed that the shaded willows are actually better food for both beetle species. On the contrary, when larvae were reared in the field under natural abiotic conditions, we found no difference in larval performance, or if any, even better performance in open habitats. Apparently, higher and more variable daily temperatures in open habitats accelerated the growth of the larvae. When adults were let to emigrate from or immigrate to potted willows, which had been grown in the same conditions but placed either in the open or shady habitats, adults preferred exposed willows. Invertebrate predators were more abundant in open habitats, but we found no differences in leaf beetle mortality by natural enemies between the habitats. Although the larval performance appeared to be approximately equal in the two habitats during the unusually warm study period, we suggest that under suboptimal temperatures the better abiotic conditions of open sites can easily override the better food provided by shaded habitats. The selection of abiotic habitat thus plays a significant role in the adaptive habitat and host plant selection of these beetles within the gradient of shadiness.     

Galerucella nymphaeae (Col., Chrysomelidae) grazing increases Nuphar leaf production and affects carbon and nitrogen dynamics in ponds

Summary The grazing effects of the waterlily beetle Galerucella nymphaeae on Nuphar lutea stands were studied in three ponds in Central Finland. Production of floating leaves of N. lutea and growth in the G. nymphaeae population were investigated in the ponds and bioenergetics of the beetle larvae in the laboratory. Combination of field and laboratory data enabled estimation of the effect of the beetle on the production of floating leaves of N. lutea and the consequences of grazing for the input of detritus from Nuphar into the ponds. Adults and larvae of G. nymphaeae consumed 3.0–6.1% of the net annual floating leaf production during the growing period. In addition to consumption losses, feeding accelerated the degradation rate of the leaves. This was associated with an increased flow of detrital material of Nuphar origin, and also with increased production of floating leaves in the ponds. These increments were estimated to be up to 3 times greater in the presence of grazing than without it. Grazing by G. nymphaeae releases substantial amounts of carbon and nitrogen bound in Nuphar, particularly in ponds with a dense Nuphar vegetation. It is hypothesized that feeding by this beetle may markedly affect the structure and functioning of such small aquatic systems.     

Matrix habitat and plant damage influence colonization of purple loosestrife patches by specialist leaf-beetles

The characteristics of the matrix, that is, the unsuitable habitat connecting host-plant patches may facilitate or limit herbivore movement thus affecting their population dynamics. We evaluated the effect of matrix habitat, distance between patches, and plant damage on movement of two leaf-beetles (Galerucella calmariensis Linnaeus and G. pusilla Duft) introduced to North America as biocontrol agents of the invasive purple loosestrife (Lythrum salicaria Linnaeus). Mark-recapture/resight experiments indicated (1) that leaf-beetles are more likely to colonize purple loosestrife patches surrounded by meadow than forest; (2) that previously attacked purple loosestrife plants are more likely to be colonized by Galerucella spp. than unattacked plants, especially in the forest habitat; and (3) that leaf beetle colonization of purple loosestrife decreased with distance from release point. Low colonization rates of purple loosestrife patches embedded in forests suggest either insufficient detection or active avoidance of such habitats. Biological control programs intend to manage dispersal of specialized insect herbivores for the purpose of sufficient and sustained control of their host plants. Such management needs to be informed by knowledge of interactions of habitat structure, plant damage, and dispersal capabilities of herbivores to facilitate release programs and control at the local and regional level.     

Dietary patterns in Perrier's sifakas (Propithecus diadema perrieri): a preliminary study

Some lemur species range into only one habitat type, whereas others range into a variety of habitats. Because plant community structure can differ between habitats, dietary patterns may vary for conspecific groups of primates that range into more than one type of habitat. The goal of our study was to determine how habitat variation influences dietary patterns in Perrier's sifakas (Propithecus diadema perrieri) that range into both dry and riparian forests in northern Madagascar. We collected 542 hr of data on the behavior and diet of two groups of P.d. perrieri from 7 June to 4 August 1998 at Camp Antobiratsy in Analamera Special Reserve, Madagascar. We computed indices of dietary diversity for each group and dietary/plant species similarity between groups. P.d. perrieri in group 1 fed predominantly in dry forest (72.7% of feeding records, n=660), whereas those in group 2 fed most often in riparian forest (73.7% of feeding records, n=666). The index of dietary similarity (0.986) was significantly higher than the index of plant species similarity (0.767). Although the P.d. perrieri in the two study groups fed predominantly in different forest habitats, they ate similar food items in very comparable proportions (but not from the same plant species). However, based on habitat availability measures, neither group fed where they were expected to feed.     

A trophic cascade in a macrophyte-based food web at the land–water ecotone

Trophic cascades may purportedly be more common in aquatic than terrestrial food webs, but herbivory on freshwater vascular plants has historically been considered low. Water lilies are an exception, suffering severe grazing damage by leaf beetles. To test whether a central prediction of cascade models—that predator effects propagate downwards to plants—operates in a macrophyte-based food web, we experimentally manipulated predation pressure on a key herbivore of water lilies in the littoral zone of a lake in Michigan, USA. Field experiments comprised combinations of caging treatments to alter the number of predators (larvae of the ladybird beetle Coleomegilla maculata) that hunt the grazers of the macrophytes (larvae of the leaf beetles Galerucella nymphaeae) on the leaves of the water lily Nuphar advena. Predatory larvae of the ladybird beetles significantly reduced grazing damage to water-lily leaves by 35–43%. The predators reduced plant damage chiefly via density-mediated effects, when lower densities of grazers translated to significant declines in plant damage. Plant damage caused by the surviving herbivores was less than predicted from individual grazing rates under predator-free conditions. This suggests that trait-mediated effects may possibly also operate in this cascade. The observed strong effect of predators on a non-adjacent trophic level concurs with an essential component of the trophic cascade model, and the cascade occurred at the ecotone between aquatic and terrestrial habitats: Nuphar is an aquatic macrophyte with emergent and floating leaves, whereas both beetle species are semi-terrestrial and use the dry, emergent and floating leaves of the water lily as habitat. Also, the cascade is underpinned by freshwater macrophytes—a group for which trophic processes have often been underappreciated in the past.     

Contrasting patterns in the invasions of European terrestrial and freshwater habitats by alien plants,insects and vertebrates

Aim To provide the first comparative overview on the current numbers of alien species that invade representative European terrestrial and freshwater habitats for a range of taxonomic groups. Location Europe. Methods Numbers of naturalized alien species of plants, insects, herptiles, birds and mammals occurring in 10 habitats defined according to the European Nature Information System (EUNIS) were obtained from 115 regional data sets. Only species introduced after ad 1500 were considered. Data were analysed by ANCOVA and regression trees to assess whether differences exist among taxonomic groups in terms of their habitat affinity, and whether the pattern of occurrence of alien species in European habitats interacts with macroecological factors such as insularity, latitude or area. Results The highest numbers of alien plant and insect species were found in human‐made, urban or cultivated habitats; if controlled for habitat area in the region, wetland and riparian habitats appeared to support relatively high numbers of alien plant species too. Invasions by vertebrates were more evenly distributed among habitats, with aquatic and riparian, woodland and cultivated land most invaded. Mires, bogs and fens, grassland, heathland and scrub were generally less invaded. Habitat and taxonomic group explained most variation in the proportions of alien species occurring in individual habitats related to the total number of alien species in a region, and the basic pattern determined by these factors was fine‐tuned by geographical variables, namely by the mainland–island contrast and latitude, and differed among taxonomic groups. Main conclusions There are two ecologically distinct groups of alien species (plants and insects versus vertebrates) with strikingly different habitat affinities. Invasions by these two contrasting groups are complementary in terms of habitat use, which makes an overall assessment of habitat invasions in Europe possible. Since numbers of naturalized species in habitats are correlated among taxa within these two groups, the data collected for one group of vertebrates, for example, could be used to estimate the habitat‐specific numbers of alien species for other vertebrate groups with reasonable precision, and the same holds true for insects and plants.     

Assessing the statistical power of genetic analyses to detect multiple mating in fishes

Blue catfish Ictalurus furcatus and channel catfish Ictalurus punctatus , two large-bodied piscivore-omnivores in Lake Texoma, Texas-Oklahoma, U.S.A., showed very high overlap in food use, but substantial differences in use of habitat during the year. Both species primarily ate fishes, aquatic insects, vegetation and detritus, terrestrial insects, seeds and zooplankton, with overall overlap = 98%. Diet breadth indices were very similar (blue catfish=4.31, channel catfish = 4.53). Quantitative and qualitative feeding varied seasonally and food habits changed ontogenetically. Feeding intensity was greatest in winter and lowest in late summer. Aquatic insects were eaten more from May to October and fishes more in winter. At body sizes from 100 to 299 mm L_s , both species primarily ate aquatic insects, terrestrial insects, fishes or zooplankton, whereas the diets of individuals >300 mm L_s of both species were dominated by fishes. Overall, their overlap in distribution across major habitat types was only 58%, with blue catfish most abundant in deep water offshore, and channel catfish more common in shallow cove habitats. Blue catfish that did occur in coves were in the deeper parts of those habitats, essentially not occurring in the littoral zone. In lakes without blue catfish, channel catfish are widely dispersed in various habitats and it is suspected that displacement of channel catfish by blue catfish may influence habitat differences of the two species in Lake Texoma. Because the spatial separation of the species also reflects their typical interspecific differences in unimpounded drainages, however, the habitat differences observed in Lake Texoma probably also reflect evolved, historical differences in ecology of the two species.     

Diet composition of Xenopus borealis in Taita Hills: effects of habitat and predator size

Frogs in the genus Xenopus are ubiquitous in sub‐Saharan Africa, yet very little is recorded on their ecology. They are commonly found in anthropogenically disturbed habitats, but how do these compare to conspecifics from natural habitats? The diet of Xenopus borealis from three different sites in Taita Hills, Kenya was established based on a sample of 77 (54 females and 23 males) specimens from two disturbed and one pristine sites. Xenopus borealis from all the sites was found to be a dietary generalist, feeding predominantly on invertebrates. A total of twelve invertebrate orders both terrestrial and aquatic were recorded in addition to amphibian eggs, tadpoles and fish. Frogs from the pristine forest were smaller and had ingested more terrestrial prey items than frogs in the disturbed open habitat ponds. The stomach content (both by mass and quantity) was independent of body size. The results suggest that X. borealis is an opportunistic generalist predator which may be constrained by food availability in its natural habitat. However, disturbed habitats provide abundant food items which are enough to significantly increase the mean size of the population.     

Enhanced growth and feeding rate in Atlantic salmon parr occupying a lacustrine habitat in the River Utsjoki, northern Scandinavia

The length, weight and stomach fullness index of salmon parr from a lake were higher than in a fluvial habitat on the same river in northern Finland, but no differences in diet composition were detected between the habitats in August. The most important food items of the parr in both habitats were insect pupae and adults. Some lake parr also fed on fish.     

Integrating species life-history traits and patterns of deforestation in amphibian conservation planning

Aim  To identify priority areas for amphibian conservation in southeastern Brazil, by integrating species life-history traits and patterns of deforestation.
Location  State of São Paulo, Brazil.
Methods  We used the software M arxan to evaluate different scenarios of amphibian conservation planning. Our approach differs from previous methods by explicitly including two different landscape metrics; habitat split for species with aquatic larvae, and habitat loss for species with terrestrial development. We evaluated the effect of habitat requirements by classifying species breeding habitats in five categories (flowing water, still water permanent, still water temporary, bromeliad or bamboo, and terrestrial). We performed analyses using two scales, grid cells and watersheds and also considered nature preserves as protected areas.
Results  We found contrasting patterns of deforestation between coastal and inland regions. Seventy-six grid cells and 14 watersheds are capable of representing each species at least once. When accounting for grid cells already protected in state and national parks and considering species habitat requirements we found 16 high-priority grid cells for species with one or two reproductive habitats, and only one cell representing species with four habitat requirements. Key areas for the conservation of species breeding in flowing and permanent still waters are concentrated in southern state, while those for amphibians breeding in temporary ponds are concentrated in central to eastern zones. Eastern highland zones are key areas for preserving species breeding terrestrially by direct or indirect development. Species breeding in bromeliads and bamboos are already well represented in protected areas.
Main conclusions  Our results emphasize the need to integrate information on landscape configuration and species life-history traits to produce more ecologically relevant conservation strategies.     

Is artificial habitat diversity a key to restoring nurseries for juvenile coastal fish? Ex situ experiments on habitat selection and survival of juvenile seabreams

Man‐made infrastructures have become ubiquitous components of coastal landscapes, leading to habitat modification that affects the abundance and diversity of marine organisms. Marine coastal fish have a complex life cycle requiring different essential habitats. One of these habitats is known as a nursery, a place where juveniles can settle in large numbers, survive, and grow to contribute to the adult population. Nurseries are mainly found in shallow, sheltered zones and are thus particularly impacted by urbanization, notably by harbors. The vertical featureless structure of docks is very unlikely to be used by juveniles, which need complex habitats to find food and shelter from predators. Recent attempts to rehabilitate the nursery function in such environments by using artificial habitats have proven efficient in increasing juvenile densities. However, nothing is known about the survival of juveniles in these habitats, preventing any conclusions on the effectiveness of this means of restoration from being drawn. Here, we set up tank experiments to test the relationship between habitat preferences and the survival rate of two species of seabream when facing stalk‐attacking combers. Habitat choice was consistent with survival results, indicating that artificial habitats might not represent unintended ecological traps for juveniles. However, the artificial habitats' effect on survival was variable between species. Therefore, our results suggest that habitat diversity might be of prime importance to sustain juveniles of different species and stress the need for the development of diverse artificial habitats to counteract the effects of seascape homogenization.     

Demography and feeding behavior of the kelp crab Taliepus marginatus in subtidal habitats dominated by the kelps Macrocystis pyrifera or Lessonia trabeculata

We studied the population and feeding ecology of the kelp crab Taliepus marginatus in subtidal kelp forests dominated by either of two morphologically different kelp species (Macrocystis pyrifera or Lessonia trabeculata) in northern Chile. The sizes and abundances of T. marginatus differed between the two kelp habitats. Kelp crabs were more abundant in the M. pyrifera forest than in the L. trabeculata forest. Size‐frequency distributions showed that juvenile and immature crabs were more common in the M. pyrifera forest than in the L. trabeculata forest, where reproductive adults predominated. The smaller crabs in the M. pyrifera habitat also consumed a higher proportion of kelp tissues than the larger crabs in the L. trabeculata habitat, which had a higher proportion of animal food in their diet. In both kelp forests, individuals of T. marginatus showed a similar pattern of nocturnal feeding over a 24‐h period, consuming more food at night than during the day. The more complex and dense forests of M. pyrifera appear to present better nursery habitats for juvenile kelp crabs than the more open and less dense forests dominated by L. trabeculata. These results suggest that the role of the two kelp habitats for T. marginatus varies during the life cycle of the kelp crabs, with M. pyrifera tending to have nursery function and L. trabeculata being more suitable as a reproductive habitat.