Gyan P. Sharma

How wide is the “knowing-doing” gap in invasion biology?

Invasion biology is a growing discipline with clear ecological, social and economic implications. A wide range of research effort is thus required to address the invasion problem, and literature on the topic is extensive. However, the extent to which the invasion biology research is addressing the challenges associated with management and mitigation of the impacts of invasions has been questioned. Using bibliometric analysis, we investigated the extent to which the literature on the subject contributes to implementation of knowledge generated, by addressing aspects of management, policy, and/or implementation; the impact of these papers as indicated by the number of citations they attract; and the geopolitical scale of focus of invasion ecology papers, particularly those that attempt to bridge the knowing-doing gap. We then compared these findings with the information needs of conservation practitioners. We first looked globally at popular search engines and then narrowed our focus to South Africa—one of three regions outside USA where researchers producing highly cited papers in invasion ecology are well represented. At this level, we conducted a content analysis of invasion ecology-related papers, of which at least one author was affiliated to a South African institution. The knowledge base in the field of invasion biology is comprised largely of research oriented towards “knowing”, while research aimed at strategically applying or implementing that knowledge is poorly represented in the scientific literature, and the scale of its emphasis is not local. Conservation practitioners clearly indicate a need for basic knowledge. However, invasion science must develop channels for effective engagement to ensure that the research is contextualised, and will deal with the complex ecological, social and economic challenges posed by invasions.

Global invasion of Lantana camara: has the climatic niche been conserved across continents?

Lantana camara, a native plant from tropical America, is considered one of the most harmful invasive species worldwide. Several studies have identified potentially invasible areas under scenarios of global change, on the assumption that niche is conserved during the invasion process. Recent studies, however, suggest that many invasive plants do not conserve their niches. Using Principal Components Analyses (PCA), we tested the hypothesis of niche conservatism for L. camara by comparing its native niche in South America with its expressed niche in Africa, Australia and India. Using MaxEnt, the estimated niche for the native region was projected onto each invaded region to generate potential distributions there. Our results demonstrate that while L. camara occupied subsets of its original native niche in Africa and Australia, in India its niche shifted significantly. There, 34% of the occurrences were detected in warmer habitats nonexistent in its native range. The estimated niche for India was also projected onto Africa and Australia to identify other vulnerable areas predicted from the observed niche shift detected in India. As a result, new potentially invasible areas were identified in central Africa and southern Australia. Our findings do not support the hypothesis of niche conservatism for the invasion of L. camara. The mechanisms that allow this species to expand its niche need to be investigated in order to improve our capacity to predict long-term geographic changes in the face of global climatic changes.

Native insects and invasive plants encounters.

Invasive plants disrupt both floral and faunal communities of the invaded regions. Influence of invasive plants on ecosystem functioning and dynamics in the invaded region can be understood by taking into consideration complex interactions between native insects and non-native plants. This review attempts to synthesize available key literature on the effects of plant invasion on native insect communities and the role of native insects in control or spread of invasive plants. The toxic or attractive nature of invasive plants will have bearing on the novel associations that native insects form with the invasive plants and consequently in regulating their population. This study examines the consequences of herbivory and pollination on invasive plants upon encounters with native insects in the invaded regions and illustrates a sequence of possible changes that native insects and invasive plants interactions may bring about within a biotic community.

Can adaptive modulation of traits to urban environments facilitate Ricinus communis L. invasiveness

This paper addresses the phenotypic variation among Ricinus communis L. populations in four urban habitat types (road verges, garbage dumps, construction debris, and natural area) in Delhi, India, by evaluating important traits such as plant height, basal circumference, seeds per plant, seed size, seed weight, specific leaf area, and reproductive index. An important biochemical marker, proline, considered as a good plant performance indicator under stress was also quantified in leaves of R. communis to evaluate its response in different habitats. Interestingly, the species showed significant variation in plant height, specific leaf area, seed size, seed weight, and leaf proline content in different habitat types. Leaf proline content was positively related to plant height, specific leaf area, and seed size while negatively related to the total number of seeds/plant. Interestingly, reproductive index, calculated as a ratio of the total number of seeds to the plant height also showed a negative relation with leaf proline content. Results indicated that R. communis exhibits adaptive modulation of growth, reproductive traits, and leaf proline content in various urban habitats which contributes to invasiveness, range expansion, and establishment of the species. The study also gives evidence of how morphological and physiological traits could directly affect invasiveness of R. communis.

Emerging Invaders from the Cultivated Croplands: An Invasion Perspective

Understanding potential sources and pathways of colonization by alien plant propagules in novel environments is crucial for assessing invasion risks posed by aggressive colonizers. With the enormous expansion and intensification of agriculture, cultivated croplands are emerging as potent sources of robust weeds and/or invaders. Ongoing increase in adaptability and evolutionary potential of agricultural systems demands our understanding to better evaluate the invasion risks to heterogeneous environments. The review intends to collate the fine ecological overlap of crops and associated plants with the plant invaders. We begin with an overview of plant invasion process and discuss invasion risks posed by cultivated croplands through putative propagule escape from crops, crop-associated weeds, and feral crop descendants, continuing with a subsequent discussion on their fate. The synthesis concludes with promising prospects for research which may generate better insights on putative invasion risks from croplands.

Urbanization and road-use determines Calotropis procera distribution in the eastern Indo-Gangetic plain, India

Urbanization can be defined as local increase in the density of inhabitants coupled with increased per capita energy consumption and extensive modifications of the environment (including the microclimate) (Gilbert 1991; Vitousek et al. 1997). This process generates unstable ecosystems that depend on large inputs of energy, and where great amounts of waste materials are accumulated (Stearns 1970; McDonnell and Pickett 1990). Despite covering a small fraction of the Earth’s surface (<5%), urban environments have a widespread influence on surrounding ecosystems (Vitousek et al. 1997; Goudie 2000). Fast growth of cities is promoting an increasing interest in urban ecosystems and in the impact of urbanization on distinct biotas (Vitousek et al. 1997; Grimm 1997). This ongoing growth of urban agglomerations leads to changes in biodiversity, including the loss of urban green cover, close vicinity forests, and other natural areas (Von der Lippe and Kowarik 2007, 2008). Ecological studies of such ecosystems are essential to reduce local and regional impacts of urbanization (Gilbert 1991; Niemela 1999).

Plastic responses to different habitat type contribute to Hyptis suaveolens Poit. Invasiveness in the dry deciduous forest of India.

A new species, when introduced into a novel environment, must become established within the constraints of site characteristics and competition with resident vegetation. Local adaptation to environmental conditions is common among plants (1). Phenotypic plasticity is potentially an important mechanism for colonization success in environmentally diverse areas and contributes to the success of invaders in diverse habitats (2, 3). Richardson and Pyšek (4) suggested that for a species to become a widespread invader it should be plastic or evolve rapidly. Studies on several colonizing species have confirmed that their populations across broad geographic and environmental ranges consisted of genetically similar populations of highly plastic genotypes (5). Rapid adaptation to small-scale environmental conditions may increase both the number of invaded habitats within regions and the dominance within habitats (6). Here we consider phenotypic plasticity as the ability for the same genotype to produce different phenotypes in response to different environments. Phenotypic plasticity is believed to be the primary strategy for these invaders to adapt to new and heterogeneous environments (6, 7). Brock et al. (8) have shown that invasiveness involves adaptive plasticity for traits that increase fitness while maintaining constancy for traits such as high dispersal potential. Phenotypic plasticity buffers organisms from environmental stochasticity and confers the ability to function in different/new environment. The success of an alien species depends on the degree of invasiveness, i.e. the potential to establish and spread (9). A few biological features can be strong predictors of potential invasiveness of a species (9, 10). Plant height and seed mass may act as indicators of both the establishment and regenerative phases of the life cycle (11, 12) and are the most pertinent traits that address competitive ability (13). Many studies have demonstrated local adaptation in local populations (14–17). We suggest that Hyptis suaveolens Poit. (American Mint; Lamiaceae), an invasive alien weed, is mainly a ‘‘plastic generalist,’’ but local adaptation through plastic responses may also play a role in its successful occupation of contrasting habitats. The study intends to test that the colonizing ability of an invader is a function of plasticity for fitness-related traits, enabling it to cope with and perhaps to benefit from habitat conditions. We evaluated the response, in terms of plant height and seed mass, of H. suaveolens to different habitats in the dry deciduous forest of India. H. suaveolens (Lamiaceae) is an erect annual woody herb, commonly 1 m in height (maximum height 1⁄4 1.5 m), and reproduces by seed (18). It is commonly known as horehound weed or mint weed, is native to the tropical America, and is now a pantropic weed (19). The leaves are ovate, 4 to 9 centimeters long, pointed at the tip, pointed to somewhat heart-shaped at the base, and toothed on the margins. The flowers occur in the axils of the leaves in long stalks. The calyx in flower is hairy and about 4 millimeters long, but soon enlarges in fruit to about 1 centimeter long with erect, stiff teeth. The corolla is blue and about 8 millimeters long, with a limb 5 millimeters in diameter; nutlets are about 1.2–1.5 millimeters long (20). The seeds are flat and characteristically dimorphic. H. suaveolens is a prolific seed producer, and heavy infestations can yield up to ’3000 seeds per square meter, forming persistent propagule banks within a short period. It is found on a variety of habitats like rail tracks, roadsides, foothills of open forests, and forest clearings and can heavily infest wastelands, particularly on arid and rocky substrates (21, 22). In India H. suaveolens was not recorded in the Vindhyan highlands in 1903 (23). However, Agrawal (24) reported heavy infestations of H. suaveolens 2 kilometers north of the super thermal power plant at Singrauli, where as recently as 10 years ago the species was not prevalent. H. suaveolens has spread to considerable stretch in open areas of this forest and can be classified as a major common and widespread invader (25, 26). Richardson and Pyšek (4) suggested that invasive species establish and proliferate across a range of environmental conditions through their plastic responses. So, we sampled H. suaveolens in two habitats across the landscapes to observe the possible plastic response of this species. We identified two habitat types: tar roads verges and natural areas in the Vindhyan dry deciduous forest of India (24813 to 24819N; 83859 to 83813E and altitude of 315–485 masl). Climate is tropical monsoonal, with mean annual rainfall of 821 mm. H. suaveolens population densities were sampled during its peak growth period (September to early October 2006) using 30 1 1 m quadrats randomly located within each habitat. Each H. suaveolens population was sampled for height, number of spikes, number of flowers on each spike, seeds on each spike, total number of seeds, seed size, and weight per 50 seeds for an average individual in each quadrat. The Reproductive Index (Ri) was estimated as the ratio of total number of seeds to the height of the plant (27, 28). The effect of different habitats on plant growth and reproductive parameters was analyzed by one-way analysis of variance (ANOVA). Differences in H. suaveolens population between the habitats were tested by Tukey’s HSD test (at p , 0.05). Linear correlation regression was performed using the SPSS statistical package (29). H. suaveolens populations showed considerable differences in plant height in different habitat conditions ( f1,581⁄4925.18, p , 0.001). The average height ranged from 75 cm to 152 cm in natural areas and along tar roads, respectively (Table 1). Interestingly, ANOVA also indicated significant differences in the number of branchlets per plant ( f1,58 1⁄4 164.61, p , 0.001), number of flowers on each branchlet ( f1,58 1⁄4 88.43, p , 0.00), number of seed on each branchlet ( f1,581⁄4 123.13, p , 0.00), total number of seed per plant ( f1,58 1⁄4 131.38, p , 0.001), average seed size ( f1,58 1⁄4 216.33, p , 0.001), and average seed weight ( f1,58 1⁄4 148.25, p , 0.001). H. suaveolens density also differed significantly among the habitats ( f1,58 1⁄4 77.60, p , 0.001). Table 1 summarizes the vegetative and reproductive characteristics of H. suaveolens in different habitats. Reproductive index is indicative of the influence of plant size on seed production and proportion of energy allocated to seeds. Large plants seem to have reproductive advantage, as they produced a large number of seeds (30). Height is an indicator of relative size and may explain the greater ability of larger plants to

Does intrinsic light heterogeneity in Ricinus communis L. monospecific thickets drive species’ population dynamics?

Ricinus communis L. colonizes heterogeneous urban landscapes as monospecific thickets. The ecological understanding on colonization success of R. communis population due to variable light availability is lacking. Therefore, to understand the effect of intrinsic light heterogeneity on species’ population dynamics, R. communis populations exposed to variable light availability (low, intermediate, and high) were examined for performance strategies through estimation of key vegetative, eco-physiological, biochemical, and reproductive traits. Considerable variability existed in studied plant traits in response to available light. Individuals inhabiting high-light conditions exhibited high eco-physiological efficiency and reproductive performance that potentially confers population boom. Individuals exposed to low light showed poor performance in terms of eco-physiology and reproduction, which attribute to bust. However, individuals in intermediate light were observed to be indeterminate to light availability, potentially undergoing trait modulations with uncertainty of available light. Heterogeneous light availability potentially drives the boom and bust cycles in R. communis monospecific thickets. Such boom and bust cycles subsequently affect species’ dominance, persistence, collapse, and/or resurgence as an aggressive colonizer in contrasting urban environments. The study fosters extensive monitoring of R. communis thickets to probe underlying mechanism(s) affecting expansions and/or collapses of colonizing populations.

It takes two to tango: variable architectural strategies boost invasive success of Lantana camara L. (sensu lato) in contrasting light environments

AbstractLantana camara L. (sensu lato) primarily invades open, well-lit environments. However, the species is expanding its range in shaded habitats. To decipher the strategies behind the species’ invasive success in contrasting light environments, key performance-related architectural and functional traits of sun and shade-dwelling individuals were estimated. L. camara exhibited significant differences in performance-related traits at whole plant, branch, and leaf-level in response to light. DNA ploidy level of each sampled individual was also estimated to determine whether observed trait differences in response to light can be related to adaptive trait modulations or to the ploidal differences. L. camara individuals dwelling in sun and shade were of similar ploidy level. Consequently, the performance of L. camara in variable light is a function of structural and functional trait differences, but not an attribute of ploidy. Sun-dwelling L. camara exhibited alterations in architecture, affecting the reproductive output, which exert local/regional propagule pressure. However, shade-dwelling individuals exhibited architectural alterations affecting plant expanse which attributes local ingress, creating a local masking effect. Both the strategies boost performance and invasive success of L. camara in contrasting light environments. The present study gives an insight that physical removal of the plant in sun and shade would imply differential benefits in the local environment.