A Lotka–Volterra competition model with seasonal succession

A complete classification for the global dynamics of a Lotka–Volterra two species competition model with seasonal succession is obtained via the stability analysis of equilibria and the theory of monotone dynamical systems. The effects of two death rates in the bad season and the proportion of the good season on the competition outcomes are also discussed.     

Clonal plants—What is their role in succession?

Fifteen successional seres from man-made habitats in central Europe were compared and the occurrence of clonal species assessed on the basis of cover data. The effects of soil moisture and nitrogen (expressed using Ellenberg indicator values) on the performance of clonal plants were also considered. Clonal species formed the dominant component of vegetation cover in the majority of the seres studied. In moist sites, their dominance was more pronounced and the peak in their relative cover occurred earlier in succession. The relative importance of species with guerilla type growth tended to increase with time in most seres and after 10 years these were mostly more important than those exhibiting phalanx type growth. The prevalence of guerilla species after 10 years was more obvious in moist seres. Clonal species were able to become dominant regardless of soil conditions, whereas the dominance of non-clonal species tended to be restricted to very wet and nutrient-poor sites. Clonal plant species appeared to maintain their dominance for a longer period than non-clonal plants.     

Are spring staging brent geese evicted by vegetation succession?

The number of spring staging brent geese on the salt marshes of the Dutch island of Schiermonnikoog increased from about 1500 individuals in the late 1960s to > 4000 in the late 1970s. Since then, numbers on Schiermonnikoog have levelled off, while the world population continued to increase. Although the extent of salt-marsh area on the island has dramatically increased over the past 20 yr, the number of brent geese on Schiermonnikoog was rather constant in this period. We hypothesise that the number of geese did not increase because of successional changes in the vegetation.
On the basis of 24 yr of counts, we show that geese had to give up older parts of the marsh. Over time, tall growing species like the shrub Atriplex portulacoides have invaded, making the marsh unsuitable for goose grazing. Newly developed marsh, however, was readily exploited by the geese. The area of older salt marsh lost due to succession was almost exactly compensated for by the development of new feeding grounds. Geese which persistently utilised the older marsh were faced with a high proportion of non-preferred species, although they still managed to assemble a diet largely composed of preferred plant species. In the older marsh, a significant reduction in the time spent foraging was also observed. We conclude that brent geese are largely excluded as vegetation succession progresses. Numbers on the island as a whole, however, are sustained due to the dynamic nature of the island. If development of new salt marshes were to be prevented, geese would be forced to abandon the salt marsh.     

Rodents as seed dispersers in a heath — oak wood succession

Summary In a Danish heathland invasion of oak shrub has taken place, the succession rate being approximately 300 m during the last 100 years. The colonisation has occurred in steps related to the delay time between seedling stage and fertility stage. Seedlings are often found in clusters originating from caches probably made by seed-eating rodents. Apodemus sylvaticus, A. flavicollis and Clethrionomys glareoles. These rodents reached autumn densities of 25–50 individuals per ha. Radioactive acorns were scatterhoarded by the rodents, which mainly deposited the acorns singly up to at least 34 m from the oak shrub (mean 15.3±8.2 m), and preferably under Empetrum nigrum mats in the walls of runways Seedlings originating from radioactive acorns were found next summer at distances of 4–37 m from the oak shrub. In early summer caches containing new seedlings had a mean size of 2.0±2.2 acorns, range 1–16; mean distance of seedlings to nearest crown projection was 24.0±23.6 m, range 1–137. Thus, rodent acorn dispersal can explain the observed succession rate of oaks into the heathland     

Cursorial spiders and succession: age or habitat structure?

Summary The structure of cursorial spider assemblages was examined along a gradient of four temperature successional communities. Species diversity (H), richness (S), and evenness (J) exhibited a dichotomy between herbaceous and woody communities rather than a progressive change with community age: all three parameters were higher in the two younger fields than in the two older woodlands, which is contrary to conventional successional theory. Species importance curves were steeper in the two woody communities. The breadth of the distribution of adult body lengths was greater in the two herbaceous communities. Indices of community similarity revealed neither a successional trend nor the vegetative dichotomy. We suggest the hypothesis that habitat structure is a more important determinant of cursorial spider diversity than successional age per se, and that the switch in dominance from herbaceous to woody vegetation is the critical change. We further suggest that competition for prey is more important to cursorial spiders in early successional (herbaceous) communities, because of a switch in the limiting resource from prey in these communities to the amount of accumulating litter (a spatial resource) in older woody stands. This may explain the greater variation in adult body size of these generalist predators in the two younger communities.     

Do bacterial and fungal communities assemble differently during primary succession?

High‐throughput sequencing technologies are now allowing us to study patterns of community assembly for diverse microbial assemblages across environmental gradients and during succession. Here we discuss potential explanations for similarities and differences in bacterial and fungal community assembly patterns along a soil chronosequence in the foreland of a receding glacier. Although the data are not entirely conclusive, they do indicate that successional trajectories for bacteria and fungi may be quite different. Recent empirical and theoretical studies indicate that smaller microbes (like most bacteria) are less likely to be dispersal limited than are larger microbes – which could result in a more deterministic community assembly pattern for bacteria during primary succession. Many bacteria are also better adapted (than are fungi) to life in barren, early‐successional sediments in that some can fix nitrogen and carbon from the atmosphere – traits not possessed by any fungi. Other differences between bacteria and fungi are discussed, but it is apparent from this and other recent studies of microbial succession that we are a long way from understanding the mechanistic underpinnings of microbial community assembly during ecosystem succession. We especially need a better understanding of global and regional patterns of microbial dispersal and what environmental factors control the development of microbial communities in complex natural systems.     

Seasonal succession of Copepoda in the Bahía Blanca estuary

The abundance and species composition of Copepoda with respect to other mesozooplanktonic groups were studied at the harbour of Ingeniero White in the inner zone of the Bahfa Blanca estuary, between July 1990 and August 1991. Maximal copepod abundances of 4.7 × 10 m^–3 and 4.9 × 10 m^–3 were observed in January 1991 and May 1991, respectively. Minimal abundances of 6 m^–3 were found in June 1990. Acartia tonsa was present throughout the year with high dominance in summer-autumn (December to May). Eurytemora affinis was present from July to October 1990 (first pulse) and from July to September 1991 (second pulse). Euterpina acutifrons was most abundant during spring 1990, whereas Paracalanus parvus was most abundant during winter-spring (July–October) 1990 and April–May 1991. The rest of the copepods were observed during winter and spring 1990 and July–August 1991. Calanoides carinatus and Labidocera fluviatilis, both species from the outer estuarine waters, were only found on two sampling dates. The proportion of meroplanktonic forms was high in certain months of the annual period considered. Differences between the copepod seasonal succession studied here and those observed during several years in the 1980's are discussed.     

Secondary plant succession: how is it modified by insect herbivory?

The effects of foliar- and root-feeding insects on the dynamics of an early successional plant community, representing the first four years of colonisation, were examined. Subterranean insect herbivores were found to increase in density with increasing successional age of the plant community. In early succession, chewing insects mainly Coleoptera (Scarabaeidae) and Diptera (Tipulidae) were dominant. This was in direct contrast to the foliar-feeding insects, which were dominated by sap-feeders (mainly Auchenorrhynchan Hemiptera).Reduction of both foliar- and root-feeding insects with appropriate insecticides had different, but dramatic, consequences for the plant community. Reducing foliar herbivory resulted in large increases in perennial grass growth, with plant species richness being reduced as the grasses outcompeted the forbs. Reducing subterranean herbivory prolonged the persistence of annual forbs, greatly increased perennial forb colonisation and, as a consequence, plant species richness. Foliar-feeding insects thus act to delay succession by slowing grass colonisation. In contrast, root-feeding insects accelerate succession by reducing forb persistence and colonisation. The structure of early successional plant communities is therefore modified by the two modes of herbivory.This paper was presented at the Vth International Congress of Ecology (INTECOL), Japan, 1990, entitled Successional Communities of Plants and Insects.     

Is succession in wet calcareous dune slacks affected by free sulfide?

Abstract. Consequences of sulfide toxicity on succession in wet calcareous dune slacks were investigated. Sulfide may exert an inhibitory effect on dune slack plants, but several pioneer species exhibit ROL (Radial Oxygen Loss) and thereby protect themselves against free sulfide. Under oxic conditions free sulfide will be oxiginated to harmless sulfate. However, successive species when not capable of ROL may be sensitive to free sulfide and cannot invade the area. Therefore, the occurrence of free sulfide may have a stabilizing effect on the pioneer vegetation. Data on the vertical distribution of oxygen, redox and sulfide were collected in mesocosms with Littorella uniflora or Carex nigra, with and without microbial mats and compared to control mesocosms. Also, in situ data were collected in a dune slack on the Frisian Island of Texel. In the mesocosms, free sulfide was detected only at nighttime in C. nigra populated mesocosms and in unvegetated units, but not in L. uniflora vegetated mesocosms. In the field, sulfide and redox profiles showed distinct differences between the groundwater exfiltration and infiltration site of the dune slack. At the exfiltration site, sulfide was only occasionally found; in contrast, measurable amounts of free sulfide were regularly found at the infiltration site of the slack. Since Phragmites australis dominates in the infiltration site of the slack, the results suggest that free sulfide accelerate the succession, rather than slowing it down by the exclusion of some plant species.     

Does seed dispersal limit initiation of primary succession in desert playas?

To investigate the initiation of primary succession in a cold-desert playa-dune complex, we studied the large-scale (2000 m) seed (diaspore) dispersal patterns at Mono Lake, California. Seeds of seven of the ten species reaching the barren playa had wind-dispersal adaptations. Rates of dispersal (numbers of seeds per square metre per day) were as much as three orders of magnitude lower on the playa than in the diverse dune vegetation. However, seed input appeared sufficient to reach potential safe sites on the playa, with a peak input of 66 ± 8 total seeds·m·d. The smooth playa surface, the virtual absence of aboveground barriers, and the high windspeed environment promote the long-distance dispersal of seeds (at least 1300 m for Chrysothamnus spp. and at least 700 m for Sarcobatus vermiculatus). The large spatial scale of sampling revealed a relatively high seed input onto the playa by the dominant pioneer species S. vermiculatus, despite the low abundance of parent vegetation in this region. All of these results implicate low rates of seed entrapment as an obstacle to establishment on this desert playa, rather than a lack of seed input.     

Old-field secondary succession in SE Spain: can fire divert it?

In the Mediterranean Basin, most cultivated areas were abandoned in the last century and are now in various stages of old-field succession. The aim of this work was to analyse the successional trajectories of these ecosystems, and to assess possible deviations in these pathways due to fire occurrence at high or low recurrence levels. Old-fields abandoned either about 50 or about 100 years ago were selected in SE Spain. Within the 50-year-old abandoned fields, plots were established which had been burned by 1, 2 and 3 fires in the last 25 years. Cover values of vascular species were sampled and then analysed by means of multivariate analysis. Euclidean distances between resulting communities were used as an indicator of the possible deviation from the unburned successional pathway. Our results pointed to the possibility that different successional pathways may exist depending on fire occurrence and recurrence. In the absence of fire, the vegetation is dominated by pioneer species, mainly Pinus. With the passage of time this vegetation will become dominated by later successional tree species (Quercus). However, when early-successional communities are affected by fire, the succession can be diverted. A single fire is enough to change Pinus forests into alternative stable states dominated by Rosmarinus officinalis shrub communities, where the colonisation of species in later successional stages is arrested. This deviation increases in high fire recurrence regimes where the vegetation changes to dwarf shrubs and herbs.     

Bacterial succession during 500?years of soil development under agricultural use

Soil bacterial succession under intensive anthropogenic disturbances is not well known. Using terminal restriction fragment length polymorphisms and 454 pyrosequencing of 16S rRNA genes, this study investigated how soil bacterial diversity and community structure changed under two agricultural land uses (paddy rice and upland cropping) in relation to soil development along a 500-year chronosequence created by intermittent reclamation of estuarine salt marshes. Multivariate analysis revealed orderly changes in soil physicochemical properties and bacterial community structure with time, confirming the occurrence of soil development and bacterial succession. Patterns of soil development and bacterial succession resembled each other, with recent land uses affecting their trajectories but not the overall direction. Succession of bacterial community structure was mainly associated with changes in ??-Proteobacteria and Verrucomicrobia. Two stages of bacterial succession were observed, a dramatic-succession stage during the first several decades when bacterial diversity increased evidently and bacterial community structure changed rapidly, and a long gradual-succession stage that lasted for centuries. Canonical correspondence analysis identified soil Na⁺, potentially mineralizable nitrogen, total phosphorous, and crystallinity of iron oxyhydrates as potential environmental drivers of bacterial succession. To conclude, orderly succession of soil bacterial communities occurred along with the long-term development of agroecosystems, which in turn was associated with soil physicochemical changes over time.     

Convergent succession of plant communities is linked to species’ functional traits

Functional traits reflecting the resource economy and growth strategy of plants vary widely both within and among ecosystems. Theory suggests that trait variation within a community may determine the relative abundance of species, though this idea requires more empirical support.We set up a long-term succession experiment in a nutrient-poor wetland, planting seedlings of twelve fenland species in different relative abundances and absolute densities, thereby creating 24 communities. The biomass of these species and the soil water and nutrient status of the system were monitored over ten years. Using these data, we could relate the changing relative abundance of species to five traits – leaf dry matter content (LDMC), leaf nitrogen concentration (LNC), specific leaf area (SLA), relative growth rate (RGR), and seed mass (SM).The initial communities converged after ten years to a common dominance–diversity structure, with two species accounting for 82% of total biomass. Soil water and nutrient conditions remained largely constant. By the end of the experiment, community trait structure had changed so that species functional traits were significantly related to their relative abundance. The most abundant species had high LDMC and SM, but low RGR and SLA, and varied little in LNC, suggesting that investment in leaf structure and retention of nutrients were most important for species dominance under low nutrient conditions. Our results provide experimental evidence that dominance–subdominance structures in plant communities are governed by functional traits.     

Testing MacArthur's minimisation principle: do communities minimise energy wastage during succession?

Robert MacArthur developed a theory of community assembly based on competition. By incorporating energy flow, MacArthur's theory allows for predictions of community function. A key prediction is that communities minimise energy wastage over time, but this minimisation is a trade‐off between two conflicting processes: exploiting food resources, and maintaining low metabolism and mortality. Despite its simplicity and elegance, MacArthur's principle has not been tested empirically despite having long fascinated theoreticians. We used a combination of field chronosequence experiments and laboratory assays to estimate how the energy wastage of a community changes during succession. We found that older successional stages wasted more energy in maintenance, but there was no clear pattern in how communities of different age exploited food resources. We identify several reasons for why MacArthur's original theory may need modification and new avenues to further explore community efficiency, an understudied component of ecosystem functioning.     

Occurrence,succession and distribution of chroöcoccal Cyanobacteria in Lake Maarsseveen I

Four species of chroöcoccal Cyanobacteria were dominant in Lake Maarsseveen I in 1987:Gomphosphaeria lacustris, Chroöcoccus sp.,Aphanocapsa sp. andMicrocystis aeruginosa. The first two were dominant in the water column, the latter two in the sediment. In the water columnAphanocapsa, Microcystis andGomphosphaeria appeared and showed highest abundance at the same time, whileChroöcoccus filled the gaps between the peaks of the others. The distribution in the sediment was related to its texture.     

Seasonal succession of phytoplankton in a lake of the Paraná river floodplain,Argentina

Phytoplankton biomass, morphological and taxonomic composition, species diversity and productivity were analyzed in a shallow lake of the Middle Paraná River floodplain (El Tigre, 31 ° 41 S and 60° 42 W), between November 1986 and July 1988. Lake inundation (filling and through-flow phases) constituted an intense long-term perturbation in the physical and chemical environment. As the lake filled with river water, K-selected species (netplanktonic filamentous bluegreens, > 37 µm, with low surface area/volume (SA/V) ratios) that had existed prior to filling (late spring 1986) were replaced in summer-fall by r-selected species (nannoplanktonic chlorophytes and cryptophytes, < 37 µm, mainly stout forms with high SA/V ratios). During the through-flow phase, lentic phytoplankton was replaced by lotic flagellate populations due to the direct flushing by river water. During the period of falling water (drainage and isolation phases), nanoplanktonic algae with similar characteristics to those of the filling phase dominated in late winter-spring. Later in the isolation phase, these were succeeded by K-selected species (netplanktonic algae, mainly motile spherical dinoflagellates and filamentous bluegreens with low SA/V ratios). Simultaneously, primary production per unit biomass decreased and total biomass and specific diversity increased. Seasonal changes of phytoplankton in floodplain lakes can be interpreted as the interaction between true successional development (as observed in the drainage and isolation phases) and intermediate disturbance. Using Reynolds' terminology, short-term disturbance (slight inflow of nutrient-rich river water) caused reversion to an earlier stage in the former succession, and long-term disturbance (lake inundation) truncated the successional progression and a new (or shifted) succession was initiated.