共查询到20条相似文献,搜索用时 15 毫秒
1.
We tested the hypothesis that positive relationships between sinking rate and irradiance were due to increases in cell density caused by accumulations of carbohydrate. In semicontinuous batch cultures of Thalassiosira weissflogii (Gru.) Fryxell el Hasle and Ditylum brightwellii (t. West) Grunow in Van Huerk, carbohydrate content was varied by growing cells under diel cycles of high or low light. Sinking rate was measured at the end of the light period and the end of the dark period, on live and heat-killed cells. No positive correlations were found between sinking rate (which varied from – 0.060 to 0.13 m·d?1) and carbohydrate content (which varied from 10 to 950 pg · cell?1), indicating that accumulations of carbohydrate did not significantly affect sinking rate. There were no large diel variations in the sinking rate of T. weissflogii, but sinking rates of D. brightwellii grown under high light ranged from being negative (i.e. cells were floating) at the end of the light period to positive at the end of the dark period. This is the first report of positive buoyancy in vegetative D. brightwellii, a phenomenon that may only occur in D. brightwellii grown under diel cycles. 相似文献
2.
Although the spectral quality of light in the ocean varies considerably with depth, the effect of light quality on different physiological processes in marine phytoplankton remains largely unknown. In cases where experiments are performed under full spectral irradiance, the meaning of these experiments in situ is thus unclear. In this study, we determined whether variations in spectral quality affected the sinking rates of marine diatoms. Semicontinuous batch cultures of Thalassiosira weissflogii (Gru.) Fryxell et Hasle and Ditylum brightwellii (t. West) Grunow in Van Huerk were grown under continuous red, white, or blue light. For T. weissflogii, sinking rates (SETCOL method) were twice as high (~0.2 m·d?1)for cells grown under red light as for cells grown under white or blue light (~0.08 m·d?1), but there were no significant differences in carbohydrate content (~105 fg·μm?3) or silica content (~ 17 fg·μ?3) to account for the difference in sinking rates. Thalassiosira weissflogii grown under blue light was significantly smaller (495 μm3) than cells grown under red light (661 μm3), which could contribute to its reduced sinking rate. However, cells grown under white light were similar in size to those grown under red light but had sinking rates not different from those of cells grown under blue light, indicating the involvement of factors other than size. There were no significant differences in sinking rate (~0.054 m·d?1) or silica content (~20 fg·μm?3) in D. brightwellii grown under red, white, or blue light, but cells grown under red light were significantly (20%) larger and contained significantly (20%) more carbohydrate per μm3 than cells grown under white or blue light. Spectral quality had no consistent effect on sinking rate, biochemical composition (carbohydrate or silica content), or cell volume in the two diatoms studied. The similarity in sinking rate of cells grown under white light compared to those grown under blue light supports the ecological validity of sinking rate studies done under white light. 相似文献
3.
To clarify the roles of zooplankton in the sedimentation of seston from the epilimnion, the sinking flux of particulate carbon
was measured along with primary production rate and zooplankton biomass from July 1996 to October 1997 at a pelagic site in
the north basin of Lake Biwa. During the study period, the flux varied seasonally from 66 to 510 mg C m−2 day−1 and was low in summer when zooplankton, composed mainly of Eodiaptomus japonicus and Daphnia galeata, were abundant. Simple correlation analysis revealed that the sinking flux correlated neither with the primary production
rate nor with the amount of sestonic carbon above the sediment trap. However, the particle elimination rate, estimated as
the difference between the primary production rate and the sinking flux, correlated positively with the zooplankton biomass.
These results suggest that zooplankton play a substantial role in decreasing the sinking flux in Lake Biwa.
Received: March 6, 2000 / Accepted: October 7, 2000 相似文献
4.
We examined the effect of the presence or absence of coccoliths on the growth and sinking rates of an oceanic isolate of the coccolithophore Emiliania huxleyi (Lohmann) Hay et Mohler isolated from the northeastern subarctic Pacific. Coccolith-forming and non-coccolith-forming (i.e. naked, nonmotile) strains were obtained from the same isolate and grown under both saturating and limiting irradiance levels with either nitrate or ammonium as the primary nitrogen source. Sinking rate, growth rate, and cell volume (excluding coccoliths) were measured for each culture. Under saturating irradiance, coccolith-forming cells grew significantly slower than naked cells, had significantly higher sinking rates, and had larger cell volumes than naked cells. Under limiting irradiance levels, growth rates of the two strains were identical, sinking rates were higher for coccolith-forming cells in stationary-phase cultures only, and cell volumes remained greater for coccolith-forming cells. The sinking rates achieved for this ubiquitous coccolithophore ranged from <0.1 to 0.5 m · d?1. Sinking rates were not statistically different between coccolith-forming and naked strains of E. huxleyi under limiting irradiance conditions for log-phase cultures, but sinking rates were greater for coccolith-forming cells under some of the other conditions tested. However, the average sinking rate was never more than twice as great as for coccolith-forming cells, with the exception of nitrate-grown, senescent cells under limiting irradiance (3.4 times greater). Cell volumes (excluding coccoliths) were consistently ca. 1.5 times greater for coccolith-forming cells than for naked cells. Nitrogen source had an effect on growth rate and cell volume, with ammonium-grown cultures growing faster and having larger cell volumes than nitrate-grown cultures of both strains. However, despite the difference in growth rate and cell volume, nitrogen source had little if any effect on sinking rate. 相似文献
5.
The effects of environmental variables, particularly irradiance, on the sinking rates of phytoplankton were investigated using cultures of Chaetoceros gracilis Schütt and C. flexuosum Mangin in laboratory experiments; these data were compared with results from assemblages in the open ocean and marginal ice zone of the Greenland Sea. In culture experiments both the irradiance under which the diatom was grown and culture growth rate were positively correlated with sinking rates. Sinking rates (ψ) in the Greenland Sea were smallest when determined from chlorophyll (mean ψchl= 0.14 m · d?1) and biogenic silica (ψsi= 0.14 m · d?1) and greatest when determined from particulate carbon (ψc= 0.55 m · d?1) and nitrogen (ψN= 0.64 m · d?1). Field measurements indicated that variations in sinking may be associated with changes in irradiance and nitrate concentrations. Because these factors do not directly affect water density, they must be inducing physiological changes in the cell which affect buoyancy. Although a direct response to a single environmental variable was not always evident, sinking rates were positively correlated with growth rates in the marginal ice zone, further indicating a connection to physiological processes. Estimats of carbon flux at stations with vertically mixed euphotic zones indicated that approximately 30% of the daily primary production sank from the euphotic zone in the form of small particulates. Calculated carbon flux tended to increase with primary productivity. 相似文献
6.
The effect of the sinking rate, or rate of medium flow (φ) on the rate of phosphate incorporation (V) by the planktonic diatoms Thalassiosira fluviatilis Hust. and T. pseudonana Hasle & Heimdal in batch and chemostat cultures was determined by passing medium at defined flow rates (0.5–25.0 mm·min?1) over algae on membrane filters. At concentrations from 1 to 100 μg phosphorus·l?1 V, increases with increasing velocity of flow, approaching a maximum value (Vm) as described by the empirical relationship: where Kφ is the sinking rate value when V = 1/2 Vm+ Vo and Vo is the uptake at 0 rate of flow. By comparing uptake at controlled flow with uptake in a vigorously stirred medium, the phosphate concentration in the cell boundary layer can be determined. The sinking rate that reduces the phosphate concentration in the boundary layer to half of nominal concentration in the medium is much lower for the larger T. fluviatilis than for T. pseudonana. For both diatoms, it is inversely related to the nominal concentration. 相似文献
7.
In this work, metabolite and antibody production kinetics of hybridoma cultures were investigated as a function of cell density and growth rate in a homogeneous perfusion reactor. Hydrophilized hollow fiber polypropylene membranes with a pore size of 0.2 m were used for medium perfusion. Oxygen was supplied to the cells through thin walled silicone tubing. The mouse-mouse hybridoma cells were grown in three identical bioreactors at perfusion rates of 1.1, 2.0, and 3.2/day for a period of eight days during which the viable cell concentrations reached stable values of 2.6×106, 3.5×106, and 5.2×106 cells/ml, respectively. Total cell densities reached values ranging from 8×106 to 1×106 cells/ml. Specific substrate consumption and product formation rates responded differently to changes in cell density and apparent specific growth rate, which were not varied independently. Using multiple regression analysis, the specific glucose consumption rate was found to vary with viable cell density while the specific glutamine uptake and lactate production rates varied with both viable cell density and apparent specific growth rate. These results suggest that cell density dictates the rate of glucose consumption while the cell growth rate influences how glucose is metabolized, i.e., through glycolysis or the TCA cycle. The specific antibody production rate was found to be a strong function of cell density, increasing as cell density increased, but was essentially independent of the specific growth rate for the cell line under study.List of Symbols MAb
monoclonal antibody
-
X
v
viable cell density (cells/ml)
-
X
d
nonviable cell density (cells/ml)
-
specific growth rate (1/day)
-
k
d
specific death rate (1/day)
-
D
dilution rate (1/day)
-
S
f
substrate concentration in feed (g/l or mM)
-
S
substrate concentration (g/l or mM)
-
P
f
product concentration in feed (g/l or g/ml)
-
P
product concentration (g/l or ug/ml)
-
q
s
specific consumption rate of substrate (g/hr/cell or mmol/hr/cell)
-
q
p
specific production rate of product (g/hr/cell)
-
q
MAb
specific production rate of monoclonal antibody (g/hr/cell)
This work was supported in part by a grant for the National Science Foundation (BCS-9157851) and by matching funds from Merck and Monsanto. We sincerely thank Mr. Roland Buchele of Akzo Inc. (Germany) for donation of the polypropylene membranes, Dr. Michael Fanger (Dartmouth Medical School) for the hybridoma cell line, Dr. Sadettin Ozturk (Verax Corp., Lebanon, NH) for technical discussions regarding reactor design, and Dr. Derrick Rollins (Iowa State University) for advice on statistical methods. 相似文献
8.
More than 1000 spores from 11 species of red algae were collected; their differences in size and sinking rates were measured using a new micro-video technique. A relationship between size and sinking rate was shown with larger spores generally sinking faster than smaller ones. Variability in spore size, or lack thereof, is a species characteristic. Cryptopleura violacea (J. G. Ag.) Kylin and Neoagardhiella baileyi (Kutz.) Wynne and Taylor were found to produce a wide range of spore sizes. Such variability in size may be related to differences in spore formation. Centrifugation was used to separate the contents of spores to show differences in them. The ecological implications of these observations are considered. 相似文献
9.
Cultures of a strain of Amphidinium carterae Hulburt isolated from a eutrophic basin in Alexandria were investigated for the optimum growth conditions, including vitamin requirements, the assimilation index and the potential toxicity of this species. A division rate of 2.7 day–1, was reached on the second and third day under optimum conditions, with and without addition of B12 and biotin. The rate of C14 assimilation per unit chlorophyll ranged from 0.2 to 5.4 mgC.(mg Chla)-1.h–1 according to the growth conditions and to cell size. As the cell density increased in the cultures, the cell size decreased and their photosynthetic efficiency increased. Toxicity of A. carterae to brine shrimp resulted from grazing and not from membrane diffusion of extracellular toxins. 相似文献
10.
Shrihari R. Kumar K. S. Gandhi K. A. Natarajan 《Applied microbiology and biotechnology》1991,36(2):278-282
Summary Experiments on the leaching of copper from chalcopyrite mineral by the bacterium Thiobacillus ferrooxidans show that, in the presence of adequate amounts of sulphide, iron-grown bacteria preferentially oxidise sulphur in the ore (through direct attachment) rather than ferrous sulphate in solution. At 20% pulp density, the leaching initially takes place by a predominantly direct mechanism. The cell density in the liquid phase increases, but the Fe2+ is not oxidised. However, in the later stages when less solid substrate is available and the cell density becomes very high, the bacteria start oxidising Fe2+ in the liquid phase, thus contributing to the indirect mechanism of leaching. Contrary to expectations, the rate of leaching increased with increasing particle size in spite of the decreasing specific surface area. This has been found to be due to increasing attachment efficiency with increase in particle size.
Offprint requests to: R. Kumar 相似文献
11.
Exponentially growing cells of Saccharomyces cerevisiae were fractionated by centrifugation in isotonic, self-generated gradients of Percoll. Rapidly growing cells, μ = 0.5
× h−1, with nearly equal length of the daughter and the parental cell cycle were fractionated according to a cell cycle-related density variation. In these cells the net rate of protein synthesis varies nearly 2-fold during the cell cycle. Subsequent separations according to cell size revealed that the highest rate is observed during G2 period. Slow-growing cells, μ = 0.2
× h−1, were fractionated on shallow Percoll gradients in a bimodal fashion, primarily as a dense daughter fraction and a composite light fraction. Thereby a marked high rate of protein synthesis in large unbudded daughter cells was revealed. Separations according to cell size revealed a cell cycle-related separation of budded cells, and the highest rate is observed, as before, in the G2 period. Irrespective of the growth rate a non-exponential increase of cell protein is thereby observed through the cell cycle of budding yeast. Septation and cell separation coincide with a low degree of ribosome exploitation. 相似文献
12.
Most cells experience an active and variable fluid environment, in which hydrodynamic forces can affect aspects of cell physiology including gene regulation, growth, nutrient uptake, and viability. The present study describes a rapid yet reversible change in cell morphology of the marine dinoflagellate Ceratocorys horrida Stein, due to fluid motion. Cells cultured under still conditions possess six large spines, each almost one cell diameter in length. When gently agitated on an orbital shaker under conditions simulating fluid motion at the sea surface due to light wind or surface chop, as determined from digital particle imaging velocimetry, population growth was inhibited and a short‐spined cell type appeared that possessed a 49% mean decrease in spine length and a 53% mean decrease in cell volume. The reduction in cell size appeared to result primarily from a 39% mean decrease in vacuole size. Short‐spined cells were first observed after 1 h of agitation at 20°C; after 8 to 12 d of continuous agitation, long‐spined cells were no longer present. The morphological change was completely reversible; in previously agitated populations devoid of long‐spined cells, cells began to revert to the long‐spined morphology within 1 d after return to still conditions. During morphological reversal, spines on isolated cells grew up to 10 μm·d?1. In 30 d the population morphology had returned to original proportions, even though the overall population growth was zero during this time. The reversal did not occur as a result of cell division, because single‐cell studies confirmed that the change occurred in the absence of cell division and much faster than the 16‐d doubling time. The threshold level of agitation causing morphology change in C. horrida was too low to inhibit population growth in the shear‐sensitive dinoflagellate Lingulodinium polyedrum. At the highest level of agitation tested, there was negative population growth in C. horrida cultures, indicating that fluid motion caused cell mortality. Small, spineless cells constituted a small percentage of the population under all conditions. Although their abundance did not change, single‐cell studies and morphological characteristics suggest that the spineless cells can rapidly transform to and from other cell types. The sinking rate of individual long‐spined cells in still conditions was significantly less than that of short‐spined cells, even though the former are larger and have a higher cell density. These measurements demonstrate that the long spines of C. horrida reduce cell sinking. Shorter spines and reduced swimming would allow cells to sink away from turbulent surface conditions more rapidly. The ecological importance of the morphological change may be to avoid conditions that inhibit population growth and potentially cause cell damage. 相似文献
13.
Phytoplankton succession and sinking rates were studied from January to December 2003 at a coastal station in the Gulf of
Trieste (northern Adriatic Sea), 200 m offshore, in a relatively undisturbed area. A conical sediment trap, moored at 15 m
depth (water depth 17 m), was used. The hypothesis if the presence of benthic and epiphytic diatoms can lead to an overestimation
of the vertical fluxes was tested. To evaluate primary and secondary sedimentation contributions, planktonic, benthic and
epiphytic diatoms were distinguished. Benthic species abundance varied throughout the year and it was related to resuspension
that strongly influenced sinking rates. All over the year, diatoms were the prevailing class in the trap material accounting
for 75.32% of the settled cells, while flagellates represented 24.11%. Dinophyceae and resting cells constituted minor components,
accounting for 0.43% and 0.14%, respectively. The gross sedimentation rates ranged from 0.006 × 108 cell m−2 d−1 in the second week of May to 6.30 × 108 cell m−2 d−1 in the third week of January with a mean annual value of 1.09 ± 1.43 × 108 cell m−2 d−1. To the primary sedimentation rate Pseudo-nitzschia seriata of the group “Nitzschia seriata complex” contributed for 49.77% followed by Chaetoceros spp. (23.88%). The major contributor to the secondary sedimentation rate was the diatom Paralia sulcata, accounting for 24.76%. Epiphytic diatoms contributed for 11.19% and 12.27% on annual average gross abundance and biomass,
respectively, reaching even 72.04% of gross abundance and 56.06% of gross biomass in the second week of August. The correlation
between temperature and the logarithm of the epiphytic biomass was statistically significant, with r = 0.66 and P < 0.001. Both in the cluster analysis and in the PCA four main groups were formed, where benthic and epiphytic species were
separately gathered. Planktonic, benthic and epiphytic forms accounted for 50.78%, 36.95% and 12.27%, respectively, calculated
on the annual average biomass. Therefore, vertical fluxes can be overestimated of 50% or more if benthic and epiphytic species
are not rejected. 相似文献
14.
Growth and mesostructure of the photosynthetic apparatus were studied in leaves of ten Triticum L. species. Plants with the Au genome were shown to develop larger leaf assimilation areas due to expanding areas of individual leaves and an increase in the absolute growth rate. Leaf and mesophyll thickness and mesophyll cell size decreased in the G-genome species. Leaf compactness, which depended on cell size and number per unit leaf area and leaf folding, determined the specific patterns of internal leaf organization in wheat species with diverse genotypes. These patterns did not affect cell plastid-to-cytoplasm ratio as shown by the stable indices of cell surface area/cell volume, cell surface area per chloroplast, and cell volume per chloroplast. The structural indices of leaf phototrophic tissues, mesophyll density, and mesophyll CO2 conductance in alloploids, as compared to diploid species, depended on both ploidy and genome constitution. 相似文献
15.
Peperzak L.; Colijn F.; Koeman R.; Gieskes W. W. C.; Joordens J. C. A. 《Journal of plankton research》2003,25(4):365-383
According to Stokes law, colony formation in phytoplanktonwould lead to enhanced sinking rates and higher sedimentationlosses if colonies had the same densities as the phytoplanktoncells they contain. In the Dutch coastal zone of the North Sea,algae settling out of the water column are subject to zoobenthosgrazing or to physical mixing into the sediment and, therefore,the formation of colonies by common diatom species and the prymnesiophytePhaeocystis globosa seems paradoxical: it would increase theprobability that sedimentation becomes a significant loss factor.However, sinking rate measurements in the Rhine region of freshwaterinfluence (ROFI) using SetCol settling columns did not reveala straightforward relationship between phytoplankton sizes (<10to >1000 µm) and sinking rates (0.4 to >2.2m day-1) of 24 autotrophic phytoplankton species and groups.In fact, under nutrient-replete conditions, the sinking ratesof the diatoms Chaetoceros radicans, Rhizosolenia shrubsoleiand Rhizosolenia stolterfothii decreased with size. The sinkingrates of large colonies of the prymnesiophyte P. globosa werealso negatively correlated with their size and positive buoyancywas observed. Chlorophyll a sinking rates exceeded 1 m day-1periodically, which is sufficient to cause significant surfacelayer loss rates over 0.2 day-1. Under stratified conditions,both chlorophyll a concentrations and sinking rates in the bottomlayer were significantly higher (+49% and +16%, respectively)than in the surface layer. These observations are discussedin relation to Stokes law, together with a critical analysisof the SetCol technique. It is concluded that: (i) SetCol givesadequate results when incubations are performed at or near insitu irradiance and temperature; (ii) sinking rates are predominantlydetermined by cell or colony density rather than their size;(iii) periodic sedimentation is an important species-specificloss process for phytoplankton in the Dutch coastal zone. Itis speculated that for diatoms with low sinking rates, autolysisis an important loss factor. 相似文献
16.
The ontogeny of larval body density and the morphological and histological events during swimbladder development were investigated in two cohorts of yellowtail kingfish Seriola lalandi larvae to understand the relationship between larval morphology and body density. Larvae <3 days post hatch (dph) were positively buoyant with a mean ± s.d . body density of 1·023 ± 0·001 g cm?3. Histological evidence demonstrated that S. lalandi larvae are initially transient physostomes with the primordial swimbladder derived from the evagination of the gut ventral to the notochord and seen at 2 dph. A pneumatic duct connected the swimbladder to the oesophagus, but degenerated after 5 dph. Initial swimbladder (SB) inflation occurred on 3 dph, and the inflation window was 3–5 dph when the pneumatic duct was still connected to the gut. The swimbladder volume increased with larval age and the epithelial lining on the swimbladder became flattened squamous cells after initial inflation. Seriola lalandi developed into a physoclist with the formation of the rete mirabile and the gas‐secreting gland comprised low‐columnar epithelial cells. Larvae with successfully inflated swimbladders remained positively buoyant, whereas larvae without SB inflation became negatively buoyant and their body density gradually reached 1·030 ± 0·001 g cm?3 by 10 dph. Diel density changes were observed after 5 dph, owing to day time deflation and night‐time inflation of the swimbladder. These results show that SB inflation has a direct effect on body density in larval S. lalandi and environmental factors should be further investigated to enhance the rate of SB inflation to prevent the sinking death syndrome in the early life stage of the fish larvae. 相似文献
17.
Sinking terminal velocities of D. middendorffiana (with and without tail spine) were measured and correlated with morphological parameters and water temperature. The main dimensions of the body showed positive growths rate correlations with the body weight. In turn, negative allometric variation was observed in the tail-spine length. The density of D. middendorffiana was age specific, and decreased as the individual grew. No differences in the sinking terminal velocities and trajectories between individuals with and without tail spine were observed. The observed hydrodynamic characteristics of D. middendorffiana were simulated by means of a model based on equivalent ellipsoids and spheres. The analysis showed that the effects of shape and the body projections are negligible on the sinking rates of D. middendorffiana. 相似文献
18.
The growth and toxin content of the dinoflagellate Alexandrium tamarense ATHK was markedly affected by culture methods. In early growth phase at lower cell density static or mild agitation methods were beneficial to growth, but continuous agitation or aeration, to some extent, had an adverse effect on cell growth. Static culture in 2 L Erlenmeyer flasks had the highest growth rate (0.38 d−1) but smaller cell size compared with other culture conditions. Cells grown under aerated conditions possessed low nitrogen and phosphorus cell yields, namely high N and P cell-quota. At day 18, cells grown in continuous agitated and 1 h aerated culture entered the late stationary phase and their cellular toxin contents were higher (0.67 and 0.54 pg cell−1) compared with cells grown by other culture methods (0.27–0.49 pg cell−1). The highest cell density and cellular toxin content were 17190 cells mL−1 and 1.26 pg cell−1 respectively in an airlift photobioreactor with two-step culture. The results indicate that A. tamarense could be grown successfully in airlift photobioreactor by a two-step culture method, which involved cultivating the cells statically for 4 days and then aerating the medium. This provides an efficient way to enhance cell and toxin yield of A. tamarense. 相似文献
19.
Accounting for morphological plasticity in phytoplankton populations is relevant for taxonomy, systematic/evolutionary, and
ecological studies. In this work, the green alga Pediastrum tetras (Ehrenberg) Ralfs was used to describe the variation in population size structure over its growth cycle and to analyze responses
to changes in biotic and abiotic factors. Pediastrum cultures reached a final stable concentration in approximately 10 days. This density (8 × 105 cells ml−1) remained stable for at least another 13 days and the intrinsic growth rate was 0.24 ± 0.01 day−1. In the exponential phase, the relative number of single cells and the proportion of large cells (with vesicles inside) within
colonies increased. When density peaked, a relative increase of single cells as well as small cells in new colonies took place.
Finally, during the stationary phase, the trend reversed: fewer single cells and a larger cell size (without vesicles) were
observed. Results indicated that nutrient supply could affect population structure, diminishing the proportion of eight-cell
colonies. Daphnia
magna Straus significantly reduced the Pediastrum population density due to predation, and this led to a significant decrease in the density of the largest colonies. In addition,
info-chemicals induced a slight increase in the density of the largest colonies compared to the control treatment. Our study
suggests a possible trade-off in P. tetras colonial size in natural environments: during the stationary growth period in a lake, Pediastrum populations tend to increase in size for efficient use of nutrients, while they decrease in size in the presence of herbivores.
Handling editor: J. Padisak 相似文献
20.
Live and dead Kinixys spekii were collected in the Sengwa Wildlife Research Area, Zimbabwe over a 12‐year period. Live tortoises were sexable at a midline plastron length of 100 mm; females were considered sexually mature at 140 mm (reached by age 9 years) and males at 120 mm (at age 7 years). Adult females were significantly larger than males, on average by 14 mm in length and by 1.43 times in mass. Mark–recapture analysis in a 2 km2 area showed a population density of sexable tortoises of 0.16 ha?1. The survival rate was estimated by recaptures, by the frequency distribution of age at death, and by the mean age of live tortoises, and averaged 0.74 year?1. Seventy‐seven to 89% of dead tortoises showed evidence of predation, depending on the criteria used. Damage occurred in characteristic forms, loss of the front or rear of the plastron, or holes in the carapace and plastron, which were attributed to predation by mammals and ground hornbills, respectively. K. spekii had similar body size and sexual size dimorphism to Mediterranean tortoises (Testudo), but population density was much lower and the mortality rate was twice as high, probably due to the abundant African predators. High mortality was offset by a rate of juvenile growth twice that of Testudo. 相似文献