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41.
Individual- and Assemblage-Level Effects of Anthropogenic Sedimentation on Snails in Lake Tanganyika 总被引:5,自引:0,他引:5
PETER B. McINTYRE † ELLINOR MICHEL‡ KRISTIN FRANCE§ ADAM RIVERS‡‡ PAUL HAKIZIMANA†† ANDREW S. COHEN 《Conservation biology》2005,19(1):171-181
Abstract: Human impacts on aquatic biodiversity are often measured at the assemblage or community level, although it has been suggested that individual-level measures are more sensitive. We evaluated the effects of anthropogenic sedimentation on endemic snails in Lake Tanganyika, East Africa, by comparing assemblage-level (i.e., species richness, evenness, and abundance) and individual-level (i.e., frequencies of predation and parasitism, fecal organic content, life history) data between sediment-disturbed and reference sites. Previous studies have indicated that sedimentation kills snails and reduces mollusc diversity in this system, but we found little evidence of changes in species richness, evenness, or snail abundance at the levels of sedimentation recorded. In contrast, individual-level data revealed a variety of differences associated with sedimentation. Frequencies of shell scarring by predatory crabs and castration by parasitic trematodes were significantly lower at disturbed sites, indicating shifts in interspecific interactions. Snails ingested large amounts of inorganic sediments at disturbed sites, suggesting a reduction in food quality. In addition, sedimentation was associated with a large downward shift in size distribution within some species and reproduction at smaller size. These strong patterns in individual-level data contrast with the lack of effects at the assemblage level. We argue that incorporating individual-level measures will often enhance the sensitivity of impact surveys and may reveal effects of disturbance on important interspecific interactions. 相似文献
42.
Gregory J. Robertson 《Behavioral ecology and sociobiology》1998,43(4-5):289-296
Hypotheses regarding the evolution and maintenance of intraspecific nest parasitism were tested with data collected during
a 3-year study of common eiders (Somateria mollissima) breeding near Churchill, Manitoba. The nest parasitism rate was highest (42.4% of nests) during the year with the highest
nest density and the best environmental conditions, and lowest (20.2% of nests) in the year with the lowest nest density and
the poorest environmental conditions. Over the nesting season, parasitic eggs were laid at the same time as normally laid
eggs. Most parasitic eggs (>75%) were laid before the host female laid her third egg. The majority of the parasitic eggs were
the first or second egg produced by the parasitic female. When a parasitic egg was laid before or on the same day as the host
female initiated her clutch, the probability of her first egg being depredated before incubation was significantly lowered.
First- and second-laid eggs suffered a high rate of predation probably because nesting females do not attend their clutch
until their second or third egg is laid. Hypotheses that some females use intraspecific nest parasitism to parasitize the
parental care of other females were inconsistent with these data. Egg adoption is a likely explanation for the prevalence
of females incubating parasitic eggs in this population.
Received: 30 September 1997 / Accepted after revision: 6 May 1998 相似文献
43.
The short-sighted selection hypothesis for parasite virulence predicts that winners of within-host competition are poorer at transmission to new hosts. Social parasitism by self-replicating, female-producing workers occurs in the Cape honeybee Apis mellifera capensis, and colonies of other honeybee subspecies are susceptible hosts. We found high within-host virulence but low transmission rates in a clone of social parasitic A. m. capensis workers invading the neighbouring subspecies A. m. scutellata. In contrast, parasitic workers from the endemic range of A. m. capensis showed low within-host virulence but high transmission rates. This suggests a short-sighted selection scenario for the host-parasite co-evolution in the invasive range of the Cape honeybee, probably facilitated by beekeeping-assisted parasite transmission in apiaries. 相似文献
44.
Coevolution is defined as specialized relationships between species that lead to a reciprocal evolutionary change. A particularly
suitable model system for studying coevolution is the interactions between obligate avian brood parasites and their hosts.
The common cuckoo (Cuculus canorus, hereafter cuckoo) is a well-known brood parasite, which utilizes a range of smaller passerines as hosts. However, warblers
of the genus Hippolais have rarely been reported as being victims of cuckoos, and furthermore, few data exist on the occurrence of antiparasite
defenses in these hosts. In this study, we examined possible host–parasite coevolution between cuckoos and eastern olivaceous
warblers (Hippolais pallida elaeica, hereafter olivaceous warblers) in three closely situated areas in northwestern Bulgaria. The olivaceous warbler has never
been reported to be a regular cuckoo host. However, the present study, carried out in 2001–2003 shows that the olivaceous
warbler is regularly and heavily parasitized by the cuckoo in this area. Parasitism rate was high (26.6%, 34/128) and consistent
among years, with some variation between areas. The cuckoo egg mimicry was moderately good, and olivaceous warbler rejection
rate of such eggs was 50%. Cuckoo eggs laid in olivaceous warbler nests had a whitish to whitish-green ground color, and the
majority appeared to be distinctly different from cuckoo eggs found in other host species in the area. The olivaceous warbler
proved to be a rather good host for cuckoos as 20.6% (7/34) of cuckoo eggs laid produced fledglings, a breeding success comparable
to other suitable hosts in Europe. This is the first in-depth study of brood parasitism in a warbler of the genus Hippolais, and cuckoos parasitizing olivaceous warblers probably represent a previously unknown gens. 相似文献