Dependence of settlement rate on suitable substrate area

نویسنده

  • H. Caswell
چکیده

Several recent ®eld studies have found disproportionately high barnacle settlement rates (expressed on a per-area basis) in situations where the amount of suitable substrate is reduced, either due to occupation by other individuals or to physical processes. We call this phenomenon the intensi®cation e€ect; it is not included in many models of benthic populations, which assume that the per-area settlement rate is a constant, or in ®eld larval-collector studies, where number of larvae caught is assumed to be a function only of larval supply. In this paper we derive a simple Markov chain model that generates the intensi®cation e€ect. It describes the fate of a settling larva, which may be washed out of the system or may attempt to settle in suitable or unsuitable substrate. If it lands on unsuitable substrate, it returns to the water column to try again. At low values of the washout rate, the per-area settlement rate decreases with increasing substrate area. At high values of the washout rate, per-area settlement rate is constant. We conducted a set of laboratory experiments in March through April 1995 with barnacle larvae (Semibalanus balanoides Linnaeus) to illustrate the predictions of the model. Substrate area was manipulated by varying the number of settling panels available, and the larval loss rate was adjusted by manipulating the residence time of larvae in the experimental units (1.5 h or 12 h). As predicted by the model, in the 12-h treatment settlement per area decreased nonlinearly as the amount of substrate increased, whereas in the 1.5-h treatment no di€erences were found. These results explain and predict the intensi®cation e€ect, and suggest that variability in the proportion of suitable substrate may be an important factor in determining variability in settlement rate. Introduction The larval phase of marine species critically in ̄uences such population phenomena as age-class strength (Hjort 1926), population ̄uctuations correlated with life history (Thorson 1950; Coe 1956), and uncorrelated densities of recruits and adults (Loosano€ 1964). Settlement and recruitment estimates have been used to compare larval input from the plankton, in spatial data or temporal series. Studies of ̄uctuations in settlement have focused on biological and physical factors in ̄uencing the settling larva. For example, Connell (1985) recognized three factors in ̄uencing invertebrate settlement rate: the number of propagules arriving, the site-speci®c hydrodynamic conditions, and behavioral factors. The resident assemblage of species can also in ̄uence settlement (e.g. Strathmann et al. 1981; Young 1988; Osman et al. 1989; Osman and Whitlatch 1995). Larvae of sessile species in hard-surface communities require space to settle. Their impact on population dynamics will depend on how settlement is a€ected by availability of free space. Many studies of barnacle settlement have documented the in ̄uence of substrate characteristics on the choice of alternative substrates and settlement [presumably related to behavior of the cyprid stage; Pye®nch (1948); Connell (1961); LeTourneaux and Bourget (1988)]. We are not concerned here with these di€erences, but with the e€ect of the amount of suitable substrate, de®ned here as free space upon which larvae will settle. Few studies have examined this e€ect; those that have, draw di€ering conclusions. Gaines and Roughgarden (1985), Navarrete and Castilla (1990), and Minchinton and Scheibling (1993) observed in the ®eld that settlement was proportional to suitable substrate: the more substrate, the more total settlement. Other ®eld studies suggest, however, that as suitable substrate becomes scarce, settlement per unit area intensi®es. Bertness et al. (1992) found that the settlement per unit area of Semibalanus balanoides increased late in the season, Marine Biology (1997) 129: 541±548 Ó Springer-Verlag 1997 Communicated by J.P. Grassle, New Brunswick J. Pineda (&) á H. Caswell Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA E-mail: [email protected] apparently as a result of favorable sites being ®lled by settlers early in the season. Pineda (1994b) found that settlement per unit area of the barnacles, Chthamalus spp., was consistently higher at the edges of a rocky shore, where suitable settlement area was scarce, than at the middle of the rocky beach, where suitable substrate was abundant, suggesting higher settlement per unit area in areas with less suitable substrate. At another rocky shore, some areas of the intertidal zone were seasonally inundated by sand, an unsuitable substrate for barnacle settlement. Areas with more sand ± less suitable substrate ± received predictably higher settlement per unit area than areas not invaded by sand. This ranking disappeared when the sand was not present, suggesting that the ranking was maintained by di€erences in the amount of suitable substrate. These observations resulted in the development of the ``decreased-substrate settlement-intensi®cation hypothesis'' (Pineda 1994b) according to which the per-area settlement rate is a decreasing function of available substrate. Hunt and Scheibling (1996) observed enhanced mussel settlement in settlement collectors relative to ice-scoured emergent rocks, and suggested that settlement intensi®cation could be related to unsuitability of ice-scoured surfaces. Osman and Whitlatch (1995) compared settlement panels with high, low, and no adult cover. They observed that settlement density of several sessile taxa was often higher in treatments with the highest density of adults, and suggested that settlement could be intensi®ed in these panels due to larvae rejecting adults as substrate, and then swimming a short distance to settle on open substrates; this would result in a settlement intensi®cation e€ect. They created a model incorporating larval discrimination, probability of settlement on adults, on free substratum, and probability of larvae being removed from the substratum. Their model predicts that the pattern of intensi®cation is determined ``by the mobility of the larvae that fail to attach''. Settlement rate can be measured in various ways (Table 1), and for the present study we are careful to specify which rates we are talking about. These are made clear in the population models of Roughgarden et al. (1985) and Roughgarden and Iwasa (1986), which identify an important set of hypotheses about the relationship between settlement and suitable substrate (free space, in their notation). Let B(t), L(t), and F(t) be the numbers of adults, larvae, and the suitable substrate within the region under consideration. Then

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Assessment of Tunnel Excavation on Surface Settlement

The expansion of underground structures is important in urban areas with high population density. In most large cities in the world, urban development is spreading along the structures. These structures are generally located at shallow depth; therefore study of shallow tunnels in urban areas is critical for development. During the excavation of tunnels in urban areas, creating the asymmetric se...

متن کامل

Settlement preferences and early migration of the tropical sea cucumber Holothuria scabra.

Settlement and post-settlement processes of the sea cucumber Holothuria scabra Jaeger were studied in the laboratory. Independent and paired choice experiments revealed that several substrates could induce metamorphosis into pentactulae, but that specific substrates favoured settlement. Leaves of seagrass Thalassia hemprichii, with or without their natural bio-film, yielded the highest settleme...

متن کامل

Complete convergence of moving-average processes under negative dependence sub-Gaussian assumptions

The complete convergence is investigated for moving-average processes of doubly infinite sequence of negative dependence sub-gaussian random variables with zero means, finite variances and absolutely summable coefficients. As a corollary, the rate of complete convergence is obtained under some suitable conditions on the coefficients.

متن کامل

Evaluation of selected substrates for collection of hatchery reared black-lip pearl oyster (Pinctada margaritifera) spat

An experiment was conducted to investigate the effect of collector materials and position on Pinctada margaritifera spat attachment. Settlement on polyethylene pipes (54.6%) was significantly higher (P < 0.05) than on plastic baskets (25%). Significantly higher (P < 0.05) spat catch was recorded from the collectors which were installed on lower height of settlement tank than upper. The number o...

متن کامل

Emergency Accommodation and Post-earthquake Logistics Management Using Damage Analysis Results

Background: Iran is an earthquake-prone country, and a considerable rural population lives in earthquake-prone areas. With many worn-out areas, incompetent houses, and relatively underdeveloped rural areas, it is necessary to pay special attention to risk reduction and subsequent measures in these areas. Materials and Methods: Among the current methods, HAZUS is one of the most common methods ...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

عنوان ژورنال:

دوره   شماره 

صفحات  -

تاریخ انتشار 1997