Modelling biological invasions: species traits,species interactions,and habitat heterogeneity

In this paper we explore the integration of different factors to understand, predict and control ecological invasions, through a general cellular automaton model especially developed. The model includes life history traits of several species in a modular structure interacting multiple cellular automata. We performed simulations using field values corresponding to the exotic Gleditsia triacanthos and native co-dominant trees in a montane area. Presence of G. triacanthos juvenile bank was a determinant condition for invasion success. Main parameters influencing invasion velocity were mean seed dispersal distance and minimum reproductive age. Seed production had a small influence on the invasion velocity. Velocities predicted by the model agreed well with estimations from field data. Values of population density predicted matched field values closely. The modular structure of the model, the explicit interaction between the invader and the native species, and the simplicity of parameters and transition rules are novel features of the model.     

Negative density-dependent mortality varies over time in a wet tropical forest,advantaging rare species,common species,or no species

Although one of the most widely studied hypotheses for high tree diversity in the tropics, the Janzen–Connell hypothesis (JC), and the community compensatory trend upon which it is based, have conflicting support from prior studies. Some of this variation could arise from temporal variation in seedling survival of common and rare species. Using 10 years of data from La Selva Biological Station in Costa Rica, we analyzed annual seedling survival and found that negative density-dependence (negative DD) was significantly stronger for rare species than for common species in 2 years and was significantly stronger for common species than for rare species in 4 years. This temporal variation in survival was correlated with climatic variables: in warmer and wetter years, common species had higher negative DD than rare species. The relationship between climate and variation in JC effects on seedling survival of common and rare species could have important consequences for the maintenance of tree species diversity in Central America, which is predicted to experience warmer and wetter years as global change proceeds.     

Time, love and species

Physiological and behavioral phenomena of many animals are restricted to certain times of the day. Many organisms show daily rhythms in their mating. The daily fluctuation in mating activity of a few insects is controlled by an endogenous clock. The fruitfly, Drosophila, is the most suitable material to characterize the genetic basis of circadian rhythms of mating because some mutants with defective core oscillator mechanism, feedback loops, have been isolated. D. melanogaster wild-type display a robust circadian rhythm in the mating activity, and the rhythms are abolished in period or timeless null mutant flies (per(01) and tim(01)), the rhythms are generated by females but not males. Disconnected (disco) mutants which have a severe defect in the optic lobe and are missing lateral neurons show arrhythmicity in mating activities. Thus, the lateral neurons seem to be essential for the circadian rhythm in mating activity of Drosophila. Furthermore, an anti-phasic relation in circadian rhythms of the mating activity was detected between D. melanogaster and their sibling species D. simulans. The Queensland fruit flies or wild gypsy moth also show species-specific mating rhythm, suggesting that species-specific circadian rhythms in mating activity of insect appear to cause a reproductive isolation.     

居群、物种与生物多样性

正受《生物多样性》主编之邀,我对洪德元先生(2016)的"生物多样性事业需要科学、可操作的物种概念"一文谈一点体会。鉴于在学术声望上我只能望洪先生之项背以及"可操作性的物种概念"之复杂性,我后悔轻率答应了撰文。但为了引起我国植物分类与系统植物学界关注这一重要问题的讨论,我不得不勉为其难。1三个目的我理解,洪先生撰写此文有三个非常明确的目的:第一,他以熟知的芍药属(Paeonia)植物为例,指出科学认识物种是有效保护我国珍稀濒危物种     

Local filters limit species diversity,but species pools determine composition

In a series of three experiments, we tested for effects of species pools, resource stress, and species interactions on four aspects of community structure: species richness, evenness, species composition, and functional group composition. We also examined whether the impacts of species interactions on the community varied with resource availability or species pool. Communities of sand dune annuals grew from seed bank samples collected from two sites in three different years, so that the species pool differed at two levels: the source site and the year of seed bank collection. Communities experienced one of three irrigation treatments and a range of sowing densities, which varied resource supply (stress) and the potential for species interactions, respectively.Species richness and evenness were most affected by local factors: higher densities and lower water availability decreased species diversity. In contrast, species composition was influenced most by the species pool. Functional group composition had an intermediate response, and was affected by both species pools and local filters.Resource stress and species interactions strongly filtered species from the community, but the identity of species remaining was variable. Furthermore, the magnitude of species interaction effects on richness and evenness varied with species pools. Thus, the outcome of species sorting among biotic and abiotic environments was dependent on the pool of available species. Contrary to predictions from theory, the effects of species interactions on the community did not vary consistently with resource levels.     

Diaporthe amygdali,a species complex or a complex species?

Delimitation of species boundaries within the fungal genus Diaporthe has been challenging, but the analyses of combined multilocus DNA sequences has become an important tool to infer phylogenetic relationships and to circumscribe species. However, analyses of congruence between individual gene genealogies and the application of the genealogical concordance principle have been somehow overlooked. We noted that a group of species including D. amygdali, D. garethjonesii, D. sterilis, D. kadsurae, D. ternstroemia, D. ovoicicola, D. fusicola, D. chongqingensis and D. mediterranea, commonly known as D. amygdali complex, occupy a monophyletic clade in Diaporthe phylogenies but the limits of all species within the complex are not entirely clear. To assess the boundaries of species within this complex we employed the Genealogical Concordance Phylogenetic Species Recognition principle (GCPSR) and coalescence-based models: General Mixed Yule-Coalescent (GMYC) and Poisson Tree Processes (PTP). The incongruence detected between individual gene phylogenies, as well as the results of coalescent methods do not support the recognition of lineages within the complex as distinct species. Moreover, results support the absence of reproductive isolation and barriers to gene flow in this complex, thus providing further evidence that the D. amygdali species complex constitutes a single species. This study highlights the relevance of the application of the GCPSR principle, showing that concatenation analysis of multilocus DNA sequences, although being a powerful tool, might lead to an erroneous definition of species limits. Additionally, it further shows that coalescent methods are useful tools to assist in a more robust delimitation of species boundaries in the genus Diaporthe.     

Cytogenetic variability in four species of Gnamptogenys Roger, 1863 (Formicidae: Ectatomminae) showing chromosomal polymorphisms,species complex,and cryptic species

Protoplasma - Gnamptogenys includes 138 described species that are widely distributed, with high diversity, in the Neotropics. Some Neotropical species have taxonomic issues, as is the case with...     

Invading species in the Eel River, California: successes, failures, and relationships with resident species

We examined invasions of non-native fishes into the Eel River, California. At least 16 species of fish have been introduced into the drainage which originally supported 12–14 fish species. Our study was prompted by the unauthorized introduction in 1979 of Sacramento squawfish, Ptychocheilus grandis, a large predatory cyprinid. From 1986 to 1990, we conducted growth and diet studies of squawfish, conducted intensive surveys of the distribution and habitat associations of both native and introduced species, and examined the nature of species-habitat and interspecies relationships. We found no evidence for increased growth or expanded feeding habits, compared to native populations, of Sacramento squawfish as they invaded the Eel River drainage. Ten of the introduced species were well established, with four species limited to a reservoir and six species established in streams. The success or failure of introductions of stream species appeared to be a function of the ability of a species to survive the fluctuating, highly seasonal, flow regime. The present mixture of native and exotic species has not formed stable fish assemblages but it seems likely that four habitat-associated assemblages will develop. The overall effect of the successful species introductions has been to assemble a group of species, with some exceptions, that are native to and occur together in many California streams. The assemblages now forming are similar to those found in other California streams. The assemblage characterized by squawfish and suckers is likely to be resistant to invasion, in the absence of human caused habitat modifications.     

Museum collections, species distributions, and rarefaction

Biological specimens in museums and herbaria are sometimes used to compare the geographical distribution of different species. In doing so, it is necessary to account for differences in the numbers of specimens. We show how rarefaction can be used for this purpose. Rarefaction is a simple mathematical method originally designed to compare species richness in communities that differed in the number of sampled individuals. We present an example involving two Phragmipedium orchid species. In this case, rarefaction suggests that the apparent difference in range can be explained by the difference in the numbers of specimens.     

Nested species subsets, gaps, and discrepancy

Chemical cues from fish can alter the behaviour of stream invertebrates in experimental tanks but their effect in natural streams has received little attention. By adding brook trout (Salvelinus fontinalis) odour to a trout stream in the Rocky Mountains of Colorado, USA, we tested whether changes in the concentration of chemical cues from visually feeding predatory fish would alter the drift of mayfly nymphs (Ephemeroptera). Stream water was piped from stream-side tanks with (odour) and without (control) three brook trout to two locations in the stream 3.5 m upstream of drift nets at six replicate sites. Five-minute drift samples were collected downstream from odour and control pipes before, during and after the release of water from the tanks into the stream during both the day and night. Almost all drift occurred at night and consisted predominantly of Baetis bicaudatus nymphs. The odour manipulation had no measurable effect on Baetis drift during the day but statistical power was low. During the night, however, the drift of large (>0.65 mm head capsule width, HCW) Baetis nymphs decreased significantly during the odour addition compared to control drift. In contrast, the drift of small nymphs (≤0.65 mm HCW) increased both during and after the odour addition in comparison to control drift. Since the stream contains brook trout (0.04–0.18 m⁻²), and water from the stream (presumably containing fish odour) altered the behaviour of fishless-stream Baetis nymphs in another experiment, we conclude that the changes in Baetis drift density were a response to an increase in the concentration of fish odour in the stream. Furthermore, we were able to detect the effect within 5 min. of odour addition, indicating that mayfly behavioural response to trout odour was rapid. These results suggest that mayflies can distinguish different concentrations of trout odour in natural streams and that the response is size-specific, according to the relative risk of predation of large and small Baetis. Received: 12 May 1998 / Accepted: 23 October 1998     

Jahnula species from North and Central America, including three new species

Three new species of loculoascomycetes collected from freshwater habitats in North America are described as new species of Jahnula (Jahnulales, Dothideomycetes). All three share these morphological features: hyaline to blackish translucent, membranous ascomata with subtending, wide, septate brown, spreading hyphae; peridia composed of large angular cells; hamathecium of septate pseudoparaphyses; 8-spored, clavate to cylindrical asci; and 1-septate, broadly fusiform, brown, multiguttulate ascospores. Four additional species, J. aquatica, J. bipolaris, J. potamophila, and J. seychellensis, are reported for the first time from the western hemisphere.     

Diversity in interspecific interactions between a nest-associating species, Pungtungia herzi, and multiple host species

Nest association in fishes affects the reproductive success of the host to varying degrees, from complete failure of the host’s reproduction to fitness advantages. Such varying impacts of nest association are considered to result from both the associate’s behavior and the characteristics of the host’s reproduction. To investigate the relationship between the impact of nest associate and host/associate ecology as well as evolutionary strategies involving nest association, we compared reproductive strategies and success between an associate East Asian minnow, Pungtungia herzi, and two host fishes (a goby, Odontobutis obscura, and a catfish, Pseudobagrus nudiceps) that have different reproductive ecologies. The associate frequently spawned around the days on which both hosts spawned, and gained a fitness advantage through continuous egg protection. Spawning by the associate had a negative effect on the survival of O. obscura eggs. Male O. obscura tended to abandon their nest when it was parasitized during the pre-spawning period. This is likely a tactic to alleviate the costs of brood parasitism. In contrast, survival of P. nudiceps eggs was consistently high in all nests, regardless of the intensity of associate’s spawning, and P. nudiceps young fed on cyprinid offspring (most probably the associate’s eggs/young) in the nest. Both P. nudiceps and P. herzi populations likely gain fitness benefits from their relationship. When comparing these two hosts with another known host, the freshwater perch Coreoperca kawamebari, the observed differences in the impact of nest association to the associate species likely correspond to differences in the spatial reproductive resources used by the respective hosts.