The effect of patch demography on the community structure of forest trees

The effect of patch demography on the structure of forest tree communities was examined using a patch-age and tree-size structured model of forest dynamics. Changes in abundance of species of different types (four different maximum tree-size classes each in two or three shade-tolerance classes) were numerically modeled in response to changes in the duration of the gap-formation-free lag phase. Average patch mortality was identical in all simulations. Tolerant species were more abundant without a lag phase due to larger variation in patch longevity, while subtolerant or intolerant species were successful when patch longevity was fixed with a long duration of lag phase. Variation in patch-age distribution facilitated species coexistence. Increasing ‘advance regeneration’, or surviving fraction at gap formation, brought about the exclusive dominance of the tolerant species. Results suggest that patch demography plays a significant role in the community organization of forest trees. In species-rich systems like tropical rain forests, longevity or canopy duration of large trees can differ among species, which brings about the variation in patch longevity, thus promoting further coexistence of species.     

The effect of patch disturbance on stream invertebrate community structure: the influence of disturbance history

The effect of disturbance history on the recovery of benthic invertebrate communities following disturbance was investigated in four streams in the Southern Alps of New Zealand. Two of the streams had a history of fluctuating discharge and temperature while the others did not. Recovery from disturbance was tested experimentally using baskets of cobbles, a third of which were disturbed every week for 9 weeks, a further third every 3 weeks and the final third left undisturbed. Algal biiomass, number of invertebrate taxa and total number of invertebrates all declined in baskets disturbed more frequently. Although the relative abundance of some taxa declined with time since the last disturbance, no taxa showed a significant decline in absolute abundance. However, several taxa showed marked increases in relative abundance in the less disturbed treatments particularly at the more stable sites. In contrast to the predictions of ecological theory, numbers of taxa and total invertebrates appeared to recover more quickly in the more complex communities at the stable sites. However, if these communities are considered to represent only stable communities, they do support the view that more complex communities will be more resilient. Community structure at the stable sites was also more similar between baskets in the undisturbed treatment than at the unstable sites, suggesting communities had reached a constant state more quickly. The more rapid recovery of communities measured at the stable sites may have been a consequence of experimental scale; disturbed patches were only 0.045 m² in area and the higher densities of invertebrates at the stable sites meant a larger pool of colonists was available following each experimental disturbance. Nevertheless, ideas of stability in ecological theory and the scale of most spate events suggest this is the appropriate scale for examining community recovery. Furthermore, the larger pool of available colonists could not explain all the differences in community response, as patterns of change in community structure at the stable sites differed considerably more from those expected by purely random colonisation processes than at the unstable sites.     

Fine structure of the mouse anterior pituitary maintained in a short-term incubation system

Summary Anterior pituitaries of mice were incubated for periods up to four hours in Krebs-Ringer bicarbonate glucose gassed with 95% O₂5% CO₂. The incubated explants survived and retained a fine structure that approximated the condition in situ. The few necrotic cells were sharply localized, and were found to be due to initial mechanical damage to the tissue.Some cells of the six granulated types exhibited slight but significant changes attributable to the liberation from the hypothalamic control: in LTH cells there was a release of preexisting granules and a development of cell organelles, whereas in other cell types there was an inhibition of release of granules and an enhanced digestion of the accumulated granules by the lysosomal system.Follicular cells responded uniquely to the changed environment by hypertrophy of the cytoplasm and were found to phagocytize cell debris. A part of non-epithelial elements of the gland showed a tendency to modulate cytologically.The author would like to express his appreciation to Mr. T. Anzai and Mr. S. Terada for their excellent technical assistance.     

Generalizing matrix structure affects the identification of least-cost paths and patch connectivity

Understanding and assessing landscape connectivity is often a primary goal when studying patchy or spatially structured populations. It is commonly accepted that the matrix plays a role in determining connectivity; however, it is not clear how the process of assessing connectivity is impacted by different ways in which the matrix may be represented, particularly if matrix structure is generalized to expedite analysis. We conducted a controlled experiment using computer simulations to evaluate the impact of increasing levels of matrix generalization on connectivity assessment using a constant arrangement of habitat patches. We varied matrix generalization for six simulated landscape patterns by adjusting the number of classes and level of pattern grain in 16 ways to yield sets of landscapes for which the matrix ranged from not generalized (i.e., heterogeneous) to completely generalized (i.e., homogeneous) while habitat placement was held constant. Least-cost paths were calculated for each landscape, and a spatial interaction model (SIM) was implemented to model the counts of patch inflows (immigration) and pairwise exchange. Applying a SIM allowed us to generate absolute outputs and explicitly compare the effect of changes to matrix generalization on connectivity. We found that both assessment of connections (i.e., measured distance and spatial delineation of least-cost paths) and patch inflows/pairwise exchange were highly sensitive to matrix generalization and that effects were inconsistent and unpredictable across the range of matrix representations, especially when estimating connectivity for individual patches. We conclude that matrix pattern may have an underappreciated effect on connectivity and that least-cost path delineation and connectivity assessment may be very sensitive to generalizations of the matrix. We suggest that sensitivity analysis of the matrix representation should be performed when conducting connectivity analyses.     

The effect of exposing a critical hydrophobic patch on amyloidogenicity and fibril structure of insulin

It is widely accepted that the formation of amyloid fibrils is one of the natural properties of proteins. The amyloid formation process is associated with a variety of factors, among which the hydrophobic residues play a critical role. In this study, insulin was used as a model to investigate the effect of exposing a critical hydrophobic patch on amyloidogenicity and fibril structure of insulin. Porcine insulin was digested with trypsin to obtain desoctapeptide-(B23–B30) insulin (DOI), whose hydrophilic C-terminal of B-chain was removed and hydrophobic core was exposed. The results showed that DOI, of which the ordered structure (predominantly α-helix) was markedly decreased, was more prone to aggregate than intact insulin. As to the secondary structure of amyloid fibrils, DOI fibrils were similar to insulin fibrils formed under acidic condition, whereas under neutral condition, insulin formed less polymerized aggregates by showing decreased β-sheet contents in fibrils. Further investigation on membrane damage and hemolysis showed that DOI fibrils induced significantly less membrane damage and less hemolysis of erythrocytes compared with those of insulin fibrils. In conclusion, exposing the hydrophobic core of insulin can induce the increase of amyloidogenicity and formation of higher-order polymerized fibrils, which is less toxic to membranes.     

Delayed start of full incubation is related to a delayed brood patch development in Magellanic Penguins Spheniscus magellanicus

Capsule: Most bird species start full incubation before the clutch is complete, others long after laying the last egg, gradually increasing the incubation temperature as incubation progresses, as is the case in Magellanic Penguins Spheniscus magellanicus.

Aims: In this study, we analysed the possible mechanisms underlying this delayed start of full incubation in Magellanic Penguins. We postulated two non-mutually exclusive, possible mechanisms: delayed development of the brood patch and/or variation in the adults’ incubation postures.

Methods: We conducted our work at Isla Quiroga, Argentina during 2011–13. We measured the development of the brood patch area, its temperature, the egg temperature and observed the postures of adult penguins.

Results: We found no association between the adults’ postures and the delayed start of full incubation, nor between brood patch temperature and the increase in egg temperature as incubation proceeded (egg age). The intercept of the curve between egg temperature and egg age was positively related to brood patch area, while the slope of the curve was negatively related.

Conclusion: Our results support the hypothesis that the shape of the curve of the increase in egg temperature as incubation proceeds is a consequence of the increase in the extension of the brood patch area.     

A comparative study of changes in the fine structure of avian eggshells during incubation

A scanning electron microscope study of the morphological changes which occur in shells of hen and quail eggs during incubation is described. The results are compared with observations on the shells of hatched eggs taken from a range of species. It was found that less change occurred in the shells of altricial species than precocial ones, the difference being associated presumably with a smaller calcium requirement for developing altricial embryos. The cores rather than the sides of mammillae appeared to be the major sites of erosion.     

Plasticity of brood patch development and its influence on incubation periods in the yellow-eyed penguin Megadyptes antipodes: an experimental approach

In many bird species, eggs laid late in the laying period hatch after a shorter incubation period than early-laid eggs. However, the mechanisms that explain these seasonal declines in incubation periods among clutches remain poorly understood. In this study we investigated the plasticity of brood patch development during incubation in yellow-eyed penguins Megadyptes antipodes and established whether differences exist in brood patch formation among early, mean and late-breeding penguins. We also examined whether brood patch development was influenced by sex and age of birds. We then placed an artificial egg in nests a few days prior to egg laying to investigate whether the presence of an egg influences brood patch development and whether an advanced brood patch development at the time of egg laying causes declines in incubation periods. Initial brood patch width on the day the first egg was laid was dependent on sex and age, while the development of brood patch width after first egg laying was slower in early-laying birds than in mean- and late-laying birds. Initial brood patch temperature as well as temperature throughout incubation was largely dependent upon sex, whereby males had higher brood patch surface temperatures than females. Placement of an artificial egg in nests stimulated successfully brood patch development in manipulated birds, so that by the time they laid their own first egg, their brood patches were wider and had higher temperatures than those of control birds. Moreover, incubation periods of first eggs from manipulated nests were significantly shorter (43.5 days) than were those from control nests (47.3 days). Thus, variation in brood patch development and related differences in incubation temperature during early incubation could contribute to seasonal declines in incubation periods.     

Neighbourhood effects in forests: implications for within-stand patch structure

1 MOSAIC, a spatially referenced Markov model was used to show how interactions among trees in a neighbourhood may influence the patch structure of forests. A series of two-species simulations were conducted with neighbourhood strength ranging from neutral (chances of species replacing each other independent of neighbourhood composition) to strong (chance of replacement for each species proportional to neighbourhood composition), and with neighbourhood sizes including 1–50 neighbours.
2 Neighbourhood strength was positively correlated with the degree of patchiness. Very high neighbourhood strength is necessary to form mono-specific patches composed of hundreds of individual trees. Intermediate neighbourhood sizes (5–12 neighbours) led to the most distinct patches where individuals were arranged so that contact between species was minimized.
3 Neighbourhood effects alone are unlikely to lead to large areas (several ha) dominated by one species. However, simulations showed that neighbourhood effects can augment small differences in the environment, resulting in large mono-specific patches.
4 Simulations with 4 and 5 species indicated that groups of species can interact to form spatially distinct communities, starting from a random mixture on a uniform environment. This implies that neighbourhood effects may be responsible for some unexplained variability in studies that attempt to relate environmental parameters to forest composition.
5 Patch structures that develop due to neighbourhood effects are usually not recognized by current vegetation classification schemes or by forest managers, and this lack of recognition could lead to the loss of certain natural spatial structures on forested landscapes.     

Effects of hypoosmotic incubation on acrosome and tail structure on canine spermatozoa

Hypoosmotic tests are widely used as valuable tests for determining sperm quality in species as varied as the human and the porcine. However, there is little information about the use of these tests in canine spermatozoa. This work evaluates the response of canine spermatozoa in hypoosmotic media in order to introduce the use of the hypoosmotic tests in the canine standard semen analysis. In this way, the incubation of canine spermatozoa in hypoosmotic media containing citrate (ORT medium, osmotic pressure = 100 mOsm) or citrate plus fructose (HOS medium, osmotic pressure = 150 mOsm) resulted in the swelling of the sperm tail. These reactions were time-dependent, reaching maximum percentages after 45 to 60 min. Optimal percentage of tail swelling with minimal effect on the viability of spermatozoa was observed at 100 to 150 mOsm. Response on sperm viability, tail swelling and acrosome detachment to hypoosmotic tests of both undiluted fresh, and 24 h-stored samples were similar. The percentage of swollen tails after both tests showed a good correlation to viability and to gross and progressive motility but not to concentration. However, acrosome detachment after both hypoosmotic tests did not correlate to any of the studied parameters. Our results indicate that the swelling observed after hypoosmotic shock could be used as a useful test in improving the standard semen analysis in the dog.     

The patch distributed producer-scrounger game

Grouping in animals is ubiquitous and thought to provide group members antipredatory advantages and foraging efficiency. However, parasitic foraging strategy often emerges in a group. The optimal parasitic policy has given rise to the producer-scrounger (PS) game model, in which producers search for food patches, and scroungers parasitize the discovered patches. The N-persons PS game model constructed by Vickery et al. (1991. Producers, scroungers, and group foraging. American Naturalist 137, 847-863) predicts the evolutionarily stable strategy (ESS) of frequency of producers that depends on the advantage of producers and the number of foragers in a group. However, the model assumes that the number of discovered patches in one time unit never exceeds one. In reality, multiple patches could be found in one time unit. In the present study, we relax this assumption and assumed that the number of discovered patches depends on the producers’ variable encounter rate with patches (λ). We show that strongly depends on λ within a feasible range, although it still depends on the advantage of producer and the number of foragers in a group. The basic idea of PS game is the same as the information sharing (parasitism), because scroungers are also thought to parasitize informations of locations of food patches. Horn (1968) indicated the role of information-parasitism in animal aggregation (Horn, H.S., 1968. The adaptive significance of colonial nesting in the Brewer's blackbird (euphagus cyanocephalus). Ecology 49, 682-646). Our modified PS game model shows the same prediction as the Horn's graphical animal aggregation model; the proportion of scroungers will increase or animals should adopt colonial foraging when resource is spatiotemporally clumped, but scroungers will decrease or animals should adopt territorial foraging if the resource is evenly distributed.     

Ecological structure of assemblages of coral reef fishes on isolated patch reefs

A 9-year study of the structure of assemblages of fish on 20 coral patch reefs, based on 20 non-manipulative censuses, revealed a total of 141 species from 34 families, although 40 species accounted for over 95% of sightings of fish. The average patch reef was 8.5 m² in surface area, and supported 125 fish of 20 species at a census. All reefs showed at least a two-fold variation among censuses in total numbers of fish present, and 12 showed ten-fold variations. There was also substantial variation in the composition and relative abundances of species present on each patch reef, such that censuses of a single patch reef were on average about 50% different from each other in percent similarity of species composition (Czekanowski's index). Species differed substantially in the degree to which their numbers varied from census to census, and in the degree to which their dispersion among patch reefs was modified from census to census. We characterize the 40 most common species with respect to these attributes. The variations in assemblage structure cannot be attributed to responses of fish to a changing physical structure of patch reefs, nor to the comings and goings of numerous rare species. Our results support and extend earlier reports on this study, which have stressed the lack of persistant structure for assemblages on these patch reefs. While reef fishes clearly have microhabitat preferences which are expressed at settlement, the variations in microhabitat offered by the patch reefs are insufficient to segregate many species of fish by patch reef. Instead, at the scale of single patch reefs, and, to a degree, at the larger scale of the 20 patch reefs, most of the 141 species of fish are distributed without regard to differences in habitat structure among reefs, and patterns of distribution change over time. Implications for general understanding of assemblage dynamics for fish over more extensive patches of reef habitat are considered.     

The relationship of oocyte diameter and incubation temperature to incubation time in temperate freshwater fish species

Based on the analysis of six egg variables and incubation temperature of 65 temperate freshwater fish species, the possible relationships between oocyte diameter, incubation time and incubation temperature were reassessed and compared to the results obtained from marine fishes. Most freshwater species have eggs (mean ± s . d . 2·19 ± 1·52 mm) larger than marine species, that are chiefly demersal and develop stuck to various substrata, such as plants or rocks. A strong negative relationship was found between incubation time ( t , days) and incubation temperature ( T , ° C): t = 186·23e^{−0·197 T} ( r ²= 0·87). A strong dependence of incubation time on oocyte diameter ( Ø , mm) and incubation temperature was also found and was defined as: log₁₀ t = 3·002 + 0·599 log₁₀ Ø − 1·91 log₁₀ ( T + 2), which explained 92% of the variance of the data set. Five major groups of species were defined based on the principal component analysis (PCA) of four quantitative variables. There were two distinct groups of salmonids, displaying demersal and non-adhesive eggs with a long incubation time at low temperature, the eggs of which required a high number of degree-days. There was a large group of species possessing small, mostly demersal and adhesive eggs developing at high temperature during a short period of time, and requiring a low number of degree-days. Between these two extremes, there was a fourth group displaying intermediate values and a fifth group including three species with large, adhesive and demersal eggs incubating at high temperatures during a short period of time. The burbot Lota lota displayed an unusual combination of variables compared to the remaining species in the data set.     

The demands of incubation and avian clutch size

We reviewed information on the demands of incubation to examine whether these could influence the optimal clutch size of birds. The results indicate that appreciable metabolic costs of incubation commonly exist, and that the incubation of enlarged clutches can impose penalties on birds. In 23 studies on 19 species, incubation metabolic rate (IMR) was not elevated above the metabolic rate of resting non-incubating birds (RMR), but contrary to the physiological predictions of King and others, IMR was greater than RMR in 15 studies on 15 species. Across species, IMR was substantially above basal metabolic rate (BMR), averaging 1.606 × BMR. Of six studies on three species performed under thermo-neutral conditions, none found IMR to be in excess of RMR. IMRs measured exclusively within the thermo-neutral zone averaged only 1.08 × BMR contrasting with the significantly higher figure of 1.72 × BMR under wider conditions. 16 of 17 studies on procellariiforms found IMR below RMR, indicating a significant difference between this and other orders. We could find no other taxonomic, or ecological factors which had clear effects on IMR. Where clutch size was adjusted experimentally during incubation, larger clutches were associated with: significantly lower percentage hatching success in 11 of 19 studies; longer incubation periods in eight of ten studies; greater loss of adult body condition in two of five studies; and higher adult energy expenditure in eight of nine studies. Given that incubation does involve metabolic costs and given that the demands of incubation increase sufficiently with clutch size to affect breeding performance, we propose that the optimal clutch size of birds may in part by shaped by the number of eggs the parents can afford to incubate.     

The influence of incubation periods on photosynthesis-irradiance curves

In phytoplankton primary production studies, samples for the determination of photosynthesis versus irradiance relationship (P-I) are usually incubated at several irradiance levels during a fixed time period, commonly 2-4 h. However, it is not clear if the use of this fixed incubation time is appropriate to study the P-I relationship in any given ecosystem. The aim of this work was to study the influence of incubation time on the P-I relationship in natural phytoplankton populations from three different coastal ecosystems: an open coastal area, an estuary, and a coastal lagoon. Physical and chemical variables, phytoplankton biomass, species composition, and P-I curves were analysed. The results showed that, in the coastal area and in the estuary, P-I relationships were time dependent, whereas in the coastal lagoon different incubation periods produced the same P-I curve. An underestimation of daily primary production, ranging from 13% to 42.5%, was calculated when data from standard incubation times (2-4 h) were used in ecosystems where P-I curves present a dynamic time-dependent behaviour. This work suggests that the response of the P-I curves to the incubation time varies with the characteristics of the ecosystem and is related to the light regime to which phytoplankton cells are adapted.