We ask whether vole herbivory in experimental grassland plots is sufficient to create an unpalatable community. In a six-year experiment, meadow voles (Microtus pennsylvanicus) reduced plant standing crop between 30% and 72%, well within the range of ungulate effects. Moreover, meadow voles reduced their available forage species by changing the plant community composition: four grass species and a legume upon which they foraged declined sharply in cover and/or number of individuals, five forbs avoided by voles increased, and two forbs neither declined nor increased with either measure. Reductions of diversity occurred when voles first defoliated the plots in 2000 but disappeared as plant species avoided by voles replaced vulnerable plants. Within six years, meadow voles created plant communities dominated by species that they did not eat.
Darwinian selection should preclude cooperation from evolving; yet cooperation is widespread among organisms. We show how kin selection and reciprocal altruism can promote cooperation in diverse 2×2 matrix games (prisoner’s dilemma, snowdrift, and hawk-dove). We visualize kin selection as non-random interactions with like-strategies interacting more than by chance. Reciprocal altruism emerges from iterated games where players have some likelihood of knowing the identity of other players. This perspective allows us to combine kin selection and reciprocal altruism into a general matrix game model. Both mechanisms operating together should influence the evolution of cooperation. In the absence of kin selection, reciprocal altruism may be an evolutionarily stable strategy but is unable to invade a population of non-co-operators. Similarly, it may take a high degree of relatedness to permit cooperation to supplant non-cooperation. Together, a little bit of reciprocal altruism can, however, greatly reduce the threshold at which kin selection promotes cooperation, and vice-versa. To properly frame applications and tests of cooperation, empiricists should consider kin selection and reciprocal altruism together rather than as alternatives, and they should be applied to a broader class of social dilemmas than just the prisoner’s dilemma.
The timing of herbivory can be an important factor in the strength and direction of plant response to herbivore damage. To determine the effect of vole herbivory timing within a growing season on tallgrass prairie forbs, we used individual plant enclosures to limit vole access to three species, Desmanthus illinoensis, Echinacea purpurea, and Heliopsis helianthoides, in an experimental restoration in northern Illinois, USA. As part of a long-term experiment, we implemented five vole access treatments in 2003: (1) vole access for the entire growing season, (2) early-season access, (3) mid-season access, (4) late-season access, and (5) no vole access. We protected all plants from herbivory in the following growing season (2004) to test whether the effects of herbivory in one growing season carried over to the next. We also tested how restoration planting design, including seeding time (June or December) and density (35 or 350 seeds/m2 of each species) affected patterns of herbivory and plant recovery. Vole access for the entire growing season was most detrimental for the growth and reproduction of all three species. In contrast, vole access for a portion of the growing season had different effects on the three species: Desmanthus growth and reproduction was negatively affected by early-season access, Echinacea reproductive output was reduced by late-season access, and Heliopsis was not affected by early-, mid-, or late-season vole access. Negative effects of continual vole access carried over to the following growing season for Desmanthus and Heliopsis, but not for Echinacea. Effects of herbivory did not carry over to the next season for Echinacea and Heliopsis when plants were accessible to voles for only part of the growing season. In contrast, Desmanthus plants exposed to early-season herbivory in one year continued to produce fewer seeds per plant after being protected from vole herbivory for a growing season. Planting density and planting season had mixed effects. Echinacea and Desmanthus were larger in plots planted in June, showing that restoration design continued to affect plant population dynamics seven years after seeding. However, there was no interaction between plant response to vole herbivory and restoration design.
Vertebrate herbivores as diverse as ungulates, geese, and rabbits preferentially feed on plants that have previously experienced herbivory. Here, we ask whether smaller grassland "cryptic consumers" such as voles (Microtus ochrogaster and M. pennsylvanicus) preferentially clip (cut stems for access to leaves or seeds) or avoid previously clipped individuals of two tallgrass prairie species (Desmanthus illinoensis and Echinacea purpurea) within a growing season. Further, we ask how these plants respond to repeated clipping within a growing season, and whether the effects of this herbivory last into the subsequent growing season. Voles preferentially clipped stems of D. illinoensis and E. purpurea plants that had been previously clipped. The exception was indiscriminant clipping of stems of E. purpurea late in the growing season when its achenes, a favorite vole food, ripened. For D. illinoensis, repeated clipping resulted in a 59% reduction in biomass, 42% lower ratio of reproductive to vegetative biomass, and 57% fewer seeds produced per plant compared with unclipped plants. These effects lasted into the following growing season in which plants were protected from voles. In contrast, the only effect of repeated clipping for E. purpurea was that the number of achenes per plant was substantially reduced by three episodes of clipping. This effect did not carry over to the next growing season. Such differences in D. illinoensis and E. purpurea response to repeated stem clipping by voles offer insights into how these small rodents can effect major changes in composition and dominance in grassland communities.
The note outlines the operation of a bit-interleaved seven-channel data-multiplexing system using universal asynchronous receiver/transmitters (u.a.r.t.s). The scheme has been used in an initial multiplexing system at Thames Polytechnic, connecting a number of terminals to a computer at a remote site over a private line. OperationThe basic structure of the system is shown in Fig. 1. The asynchronous data stream from the peripherals is synchronised to a central clock by assigning a u.a.r.t. to each peripheral. Asynchronous characters are fed into the receiver section of the u.a.r.t.; on complete reception of a character, the character bits are fed in parallel to the transmitter section, and fed out serially under the control of a central clock.The serial outputs of these u.a.r.t.s are fed in parallel to the transmitter-data inputs of another u.a.r.t. which is clocked at ten times the rate of the synchronising u.a.r.t.s. Here, in a single bit time of the synchronising u.a.r.t.s, a 10-bit word, consisting of a start bit, two stop bits and the seven input data bits from the synchronising u.a.r.t.s, can be fed serially out of this fast u.a.r.t. on receipt of a transmitter-data strobe pulse. Control logic provides such a pulse once per bit time of the synchronising u.a.r.t.s, and ensures that this pulse cannot coincide with a transition of the clock line to the synchronising u.a.r.t.s. The form of the output word from the fast u.a.r.t. is shown in Fig. 2.The receiver section of the fast u.a.r.t. is used to receive a similar output signal from a remote site. The incoming bits in a serial word represent the current bits from seven separate lines at the remote site, and these appear in parallel on the received-data-bit outputs. Hence, each received-databit output carries the bit stream originating from a source at the remote site.The synchronising u.a.r.t.s are clocked at rate corresponding to the nominal 100 bits/s plus 0-75%. This is necessary because it is possible for terminal bit rates to exceed the nominal value by this amount (CCITT recommendation S6). Should the terminal bit rate exceed the bit rate of the synchronising u.a.r.t.s, some characters would be missed. TestingTests were carried out by cascading all seven channels. This caused all seven channels to operate simultaneously, although at any time all the channels would be carrying different characters due to the character delays in the synchronising u.a.r.t.s. A microprocessor was arranged to output a data stream from its store, and receive this same data stream after transmission both ways through the seven channels. The received data stream was compared with the Paper T135 C, received 3rd December 1977 Mr. Birch and Mr. Sullivan are with the School of Electrical and Electronic Engineering, Thames Polytechnic, Riverside House Annexe, Beresford Street, London SE18 6BU, Englandstore contents by the microprocessor, and errors were indicated. Tests of up to 8 hours continuous data were run without any errors being indicated, although deliberately injected error...
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