Phylogenetic diversity and the functioning of ecosystems

Phylogenetic diversity (PD) describes the total amount of phylogenetic distance among species in a community. Although there has been substantial research on the factors that determine community PD, exploration of the consequences of PD for ecosystem functioning is just beginning. We argue that PD may be useful in predicting ecosystem functions in a range of communities, from single-trophic to complex networks. Many traits show a phylogenetic signal, suggesting that PD can estimate the functional trait space of a community, and thus ecosystem functioning. Phylogeny also determines interactions among species, and so could help predict how extinctions cascade through ecological networks and thus impact ecosystem functions. Although the initial evidence available suggests patterns consistent with these predictions, we caution that the utility of PD depends critically on the strength of phylogenetic signals to both traits and interactions. We advocate for a synthetic approach that incorporates a deeper understanding of how traits and interactions are shaped by evolution, and outline key areas for future research. If these complexities can be incorporated into future studies, relationships between PD and ecosystem function bear promise in conceptually unifying evolutionary biology with ecosystem ecology.     

The structure of ecosystems

Input-output theory is developed for an ecosystem in terms of production and respiration energy flows. The theory reveals a “structure” of the system by demonstrating the direct and indirect energy flow dependence of each member of the system upon the others. A method for tracing the direct and indirect element flows through the ecosystem is proposed.The structure is determined for two examples and a perturbation technique for the energy flow is suggested.     

The significance of fish in the marine Antarctic ecosystems

Paper presented at the Symposium on Polar regions: the challenge for biological and ecological research organised by the Swiss Committee for Polar Research, Basel on 2 October 1992     

The significance of latitudinality in Himalayan mountain ecosystems

This paper argues that the altitude-oriented mixed mountain agriculture model in which mountain dwellers move to higher altitudes in summer and lower ones in winter does not fit the empirical situation in many areas of the Himalayas where north-south or latitudinally differentiated habitat and production zones play important and, in some instances, central roles.     

Lignotubers and burls— their structure,function and ecological significance in Mediterranean ecosystems

Vegetative regeneration provides for immediate tissue replacement and reestablishment of the “parent” genotype, after the aerial canopy of a perennial plant is partially or wholly destroyed. If the frequency of destruction of above-ground biomass (e.g., by fire) is such that tissue replacement (production) is the predominant mode of growth, this regenerative capacity may preadapt the plant for reproduction via vegetative growth. In the perennial shrubs of the California chaparral, and in other similar Mediterranean-type ecosystems, one of the most significant modes of reproduction is characterized by sprouting after injury of new stem or root tissue from an ontogenetically produced swollen stem base/root crown known as a lignotuber (or “burl”). Lignotubers have been well described inEucalyptus (Myrtaceae) and observed in other families in the Mediterranean-type climate regions. “Burls” of shrubs in the family Ericaceae are morphologically similar to lignotubers. The term “burl” is vague in meaning, since it has been used to describe any anomalous or unusual woody structure with a swirled grain. The term lignotuber, which has a more restricted usage referring only to ontogenetically produced structures, should henceforth be used to describe these swollen “root crowns.” Investigations of lignotuber (burl) anatomy have revealed that the wood contains dormant buds, carbohydrates, and nutrients necessary for bud development. Reproductive strategies and tactics have evolved partially in response to the frequency and severity of disturbance (e.g., fire in shrublands of Mediterranean-type ecosystems). Reproductive strategies are defined by the timing and mode of production and reproduction. Reproductive tactics are the options of “reproductive effort” and energy allocation within each strategy. In the chaparral, fynbos, macchia, etc., one prevalent tactic in the sprouting strategy is the allocation of energy to the woody structure which has sprouting as its prime function—the lignotuber.     

Post-fire functioning of Eastern Cisbaikalian forest ecosystems

The post-fire dynamics of Eastern Cisbaikalian forest ecosystems is analyzed. Forest productivity is shown to be reduced by litter and humus ground fires. The study characterizes understory and soil changes after fires of various severities and remoteness.     

The structure and functioning of the couplon in the mammalian cardiomyocyte

The couplons of the cardiomyocyte form nanospaces within the cell that place the L-type calcium channel (Ca_v1.2), situated on the plasmalemma, in opposition to the type 2 ryanodine receptor (RyR2), situated on the sarcoplasmic reticulum. These two molecules, which form the basis of excitation–contraction coupling, are separated by a very limited space, which allows a few Ca²⁺ ions passing through Ca_v1.2 to activate the RyR2 at concentration levels that would be deleterious to the whole cell. The limited space also allows Ca²⁺ inactivation of Ca_v1.2. We have found that not all couplons are the same and that their properties are likely determined by their molecular partners which, in turn, determine their excitability. In particular, there are a class of couplons that lie outside the RyR2-Ca_v1.2 dyad; in this case, the RyR2 is close to caveolin-3 rather than Ca_v1.2. These extra-dyadic couplons are probably controlled by the multitude of molecules associated with caveolin-3 and may modulate contractile force under situations such as stress. It has long been assumed that like the skeletal muscle, the RyR2 in the couplon are arranged in a structured array with the RyR2 interacting with each other via domain 6 of the RyR2 molecule. This arrangement was thought to provide local control of RyR2 excitability. Using 3D electron tomography of the couplon, we show that the RyR2 in the couplon do not form an ordered pattern, but are scattered throughout it. Relatively few are in a checkerboard pattern—many RyR2 sit edge-to-edge, a configuration which might preclude their controlling each other's excitability. The discovery of this structure makes many models of cardiac couplon function moot and is a current avenue of further research     

The structure and functioning of the couplon in the mammalian cardiomyocyte

The couplons of the cardiomyocyte form nanospaces within the cell that place the L-type calcium channel (Ca(v)1.2), situated on the plasmalemma, in opposition to the type 2 ryanodine receptor (RyR2), situated on the sarcoplasmic reticulum. These two molecules, which form the basis of excitation-contraction coupling, are separated by a very limited space, which allows a few Ca(2+) ions passing through Ca(v)1.2 to activate the RyR2 at concentration levels that would be deleterious to the whole cell. The limited space also allows Ca(2+) inactivation of Ca(v)1.2. We have found that not all couplons are the same and that their properties are likely determined by their molecular partners which, in turn, determine their excitability. In particular, there are a class of couplons that lie outside the RyR2-Ca(v)1.2 dyad; in this case, the RyR2 is close to caveolin-3 rather than Ca(v)1.2. These extra-dyadic couplons are probably controlled by the multitude of molecules associated with caveolin-3 and may modulate contractile force under situations such as stress. It has long been assumed that like the skeletal muscle, the RyR2 in the couplon are arranged in a structured array with the RyR2 interacting with each other via domain 6 of the RyR2 molecule. This arrangement was thought to provide local control of RyR2 excitability. Using 3D electron tomography of the couplon, we show that the RyR2 in the couplon do not form an ordered pattern, but are scattered throughout it. Relatively few are in a checkerboard pattern--many RyR2 sit edge-to-edge, a configuration which might preclude their controlling each other's excitability. The discovery of this structure makes many models of cardiac couplon function moot and is a current avenue of further research.     

Consequences of plant-herbivore coevolution on the dynamics and functioning of ecosystems

The potential consequences of plant-herbivore coevolution for ecosystem functioning are investigated using a simple nutrient-limited ecosystem model in which plant and herbivore traits are subject to adaptive dynamics. Although the ecological model is very simple and always reaches a stable equilibrium in the absence of evolution, coevolution can generate a great diversity of dynamical behaviors. The evolutionary dynamics can lead to a stable equilibrium. If the evolution of plants is fast enough, certain values of the trade-off parameters lead to complex evolutionary cycles bounded by physiological constraints. The dynamical behavior of the model is very different when the dynamics of inorganic nutrient is ignored and plant competition is modeled by a logistic growth function. This emphasizes the importance of including explicit nutrient dynamics in studies of plant-herbivore coevolution.     

Moss functioning in different taiga ecosystems in interior Alaska

Summary Carbon dioxide exchange rates in excised 2-year-old shoot sections of five common moss species were measured by infrared gas analysis in mosses collected from different stands of mature vegetation near Fairbanks, Alaska. The maximum rates of net photosynthesis ranged from 2.65 mg CO₂ g^-1h^-1 in Polytrichum commune Hedw. to 0.25 in Spagnum nemoreum Scop. Intermediate values were found in Sphagnum subsecundum Nees., Hylocomium splendens (Hedw.) B.S.G., and Pleurozium schreberi (Brid.) Mitt. Dark respiration rates at 15°C ranged from 0.24 mg CO₂ g^-1h^-1 in S. subsecundum to 0.57 mg CO₂ g^-1h^-1 in H. splendens. The dark respiration rates were found to increase in periods of growth or restoration of tissue (i.e., after desiccation). There was a strong decrease in the rates of net photosynthesis during the winter and after long periods of desiccation.Due to increasing amounts of young, photosynthetically active tissue there was a gradual increase in the rates of net photosynthesis during the season to maximum values in late August. As an apparent result of constant respiration rates and increasing gross photosynthetic rates, the optimum temperature for photosynthesis at light saturation and field capacity increased during the season in all species except Polytrichum, with a corresponding drop in the compensation light intensities. Sphagnum subsecundum seemed to be the most light-dependent species.Leaf water content was found to be an important limiting factor for photosynthesis in the field. A comparison between sites showed that the maximum rates of net photosynthesis increased with increasing nutrient content in the soil but at the permafrostfree sites photosynthesis was inhibited by frequent moisture stress.     

The neural crest,A multifaceted structure of the vertebrates

In this review, several features of the cells originating from the lateral borders of the primitive neural anlagen, the neural crest (NC) are considered. Among them, their multipotentiality, which together with their migratory properties, leads them to colonize the developing body and to participate in the development of many tissues and organs. The in vitro analysis of the developmental capacities of single NC cells (NCC) showed that they present several analogies with the hematopoietic cells whose differentiation involves the activity of stem cells endowed with different arrays of developmental potentialities. The permanence of such NC stem cells in the adult organism raises the problem of their role at that stage of life. The NC has appeared during evolution in the vertebrate phylum and is absent in their Protocordates ancestors. The major role of the NCC in the development of the vertebrate head points to a critical role for this structure in the remarkable diversification and radiation of this group of animals. Birth Defects Research (Part C) 102:187–209, 2014. © 2014 Wiley Periodicals, Inc.     

Identifying the structure of cycling in ecosystems

Given a steady-state network of flows within an ecosystem, it becomes possible to systematically and automatically enumerate all distinct simple cycles of flows. Cycles may be grouped according to shared smallest arcs. The original network may then be decomposed into a web of purely cycled flow and a residual acyclic graph consisting of once-through pathways. The aggregation of elementary cycles according to shared vulnerable arcs seems particularly effective in locating those transfers which stress is most likely to disturb.     

Exploitation interactions and the structure of ecosystems

The techniques of input-output economics have recently been applied to describing energy flow through ecosystems. This paper considers interactions arising from resource exploitation, and in particular competition, in light of these concepts. An extended definition of niche overlap, including indirect exploitation, is developed and applied to developing an extended view of competition. It is shown that competing species may in fact interact in numerous and often counteracting ways.     

The evolution,structure and functioning of stomata

Summary

The anatomy and ultrastructure of guard cells from a range of species varying from the primitive types, such as mosses, to the advanced grasses and orchids are described. An attempt is made to trace the lines along which stomata developed and to define what might be considered advanced stomata. Additionally, the differentiation of guard cells from guard mother cells is discussed. Of particular note is the preprophase band of microtubules which marks the zone where the future cell wall will form and the movement of the spindle and developing cell plate through 45 degrees. The structure and function of guard cells are intimately linked. Stomata are turgor regulated valves; the osmotica for absorbing water during opening are K⁺, Cl^- and malate anions which accumulate in the guard cell vacuoles. Upon stomatal closure, K⁺ and Cl^- exit from the guard cells while at least some of the carbon from malate is channelled into starch and there is a resultant loss of guard cell turgor. The Calvin cycle may be absent or of low activity in guard cell chloroplasts and under those circumstances a source of carbon and energy to sustain the guard cells is needed. Hence it is believed that sucrose is transported into the guard cells from mesophyll cells. A brief consideration of the mechanism by which the ions are transported across the plasma membrane and tonoplast is made: the driving force for the K⁺, Cl^- and malate movement across the membranes is the proton motive force set up by proton-pumping ATPases.