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Science lab on the population growth of flour beetles

Four treatments were set up to compare different levels of environmental heterogeneity. We established high, low, moderate, and no heterogeneity. These levels were estimated by the different amounts of food offered to each population. To investigate how risk spreading works, a stochastic model for two subpopulations was employed. The high heterogeneity treatment resulted in the longest persistence, even though survival analysis revealed no significant science lab on the population growth of flour beetles among treatments.

The magnitude of differences in growth rates among subpopulations is probably associated with persistence. Understanding temporal fluctuations in population abundance is essential in analyzing population dynamics. An approach considering both time and space is useful in detecting two potentially important factors in population dynamics: The spatial component of population dynamics has inspired a variety of modeling formalisms, which differ in grain and detail Hanski, 1994.

Several types of models have been used to explore the role of spatial heterogeneity in population, metapopulation, and community dynamics Taylor, 1988; Kareiva, 1990; Hanski, 1991, 1994.

Most metapopulation models are based on measures of presence or absence in habitat patches interconnected by migration Hanski, 1991, 1994. They are stochastic because colonization and extinction of patches are random events contingent on patch area and relative spatial isolation Roughgarden, 1998; Renshaw, 1999.

A source is a subpopulation in which births exceed deaths and emigration exceeds immigration, and which thus may be considered a net exporter of individuals Pulliam, 1988. A sink, on the other hand, is a subpopulation in which deaths exceed births and immigration exceeds emigration Pulliam, 1988.

A population in a variable environment with exchange of individuals between subpopulations will experience variation in both time and space. At any given moment, each subpopulation may not be perfectly correlated with other subpopulations Ranta et al. Hence, both the degree of correlation with environmental variation and the dispersal pattern among subpopulations could affect both local and global dynamics.

One approach in examining the complexity of these relationships is to experimentally investigate populations under carefully controlled conditions. Flour beetles of the genus Tribolium have been used in this fashion for over sixty years Chapman, 1928; Park et al. Laboratory populations are easily cultured and many species can complete their life cycle in less than a month Dennis et al.

Population attributes such as density and age structure are readily measured and the populations themselves can be replicated Dennis et al. Some species of Tribolium are cannibalistic Park et al. Adults feed on eggs, larvae, pupae, and callows while larvae eat eggs, pupae, and callows. Neither larvae nor adults eat mature adults and larvae do not feed on larvae Dennis et al.

This level of complexity renders the Tribolium system an excellent experimental model for theoretical and empirical studies.

In the present study we analyzed both experimentally and theoretically the effect of migration on persistence time and population growth of experimental coupled populations of Tribolium castaneum in two different environments. Our study is an attempt to evaluate the behavioral patterns of populations as well as science lab on the population growth of flour beetles dynamics of extinction through interactions between environmental heterogeneity and interpatch migration.

We believe that the Tribolium system can illustrate very well how the source populations may rescue sink populations in a population structure with two dimensions: Different amounts of food were offered to each pair. Four treatments were set up to compare different levels of environmental heterogeneity: Of these 50, one bottle received the dispersing fraction and the other received the non-dispersing fraction.

The initial sizes of paired populations were always 5 for vials with 5, 10, 15, and 20 grams, and 45 for vials with 35, 30, 25, and 20 grams.

There were twelve replicate pairs per treatment. The experimental protocol produced discrete generations at seven-week intervals. Adults were introduced to the medium for one week to oviposit and then removed, thus simulating adult mortality and destabilizing these populations Costantino et al.

Seven weeks later, adults from the subsequent generation were counted. These output numbers were used to determine the initial size of the next generation, according to the following formula: Nd is then used as Nt to begin the next generation. Six generations were investigated for a total period of 35 weeks. Statistical analysis Survival analysis was run using Kaplan-Meier survival curves and the log-rank test to compare survival curves from each treatment.

In short, it is the probability that an organism will migrate Roughgarden, 1998. Nx,t is the number of individuals at time t in the subpopulation at location x, where x is 1 or 2. The geometric growth rate at location x at time t is r. If m is zero, the equations describe two separate uncoupled populations.

  • Tested studies for laboratory teaching proceedings of the association for biology laboratory education vol 33, , using flour beetles tribolium confusum in population growth studies sheryl;
  • At any given moment, each subpopulation may not be perfectly correlated with other subpopulations Ranta et al;
  • In a classic study, Jillson 1980 investigated the responses of T;
  • In short, it is the probability that an organism will migrate Roughgarden, 1998.

Two growth rates r1 and r2 were employed in the simulations obtained from N1 and N2 subpopulations to simulate the effect of environmental stochasticty. Using a random number generator, the growth rates were set in each loop of the equations. Global extinctions were observed in all treatments, although different numbers of extinct populations were found for each environment.

With high environmental heterogeneity 5 and 35 g of foodsix populations of Tribolium became extinct within three generations 14 weeks. The pattern of population persistence is shown in Fig. All the coupled populations extinct within three generations exhibited the same growth rates: The simulations run indicated global extinction by the third generation Fig.

  • There is evidence that cannibalism can facilitate colonization of new environments since cannibals can use intraspecific predation to compensate for resource scarcity in places to which invader species have not yet adapted Johansson, 1996; Wissinger et al;
  • There is evidence that cannibalism can facilitate colonization of new environments since cannibals can use intraspecific predation to compensate for resource scarcity in places to which invader species have not yet adapted Johansson, 1996; Wissinger et al;
  • A population in a variable environment with exchange of individuals between subpopulations will experience variation in both time and space;
  • Four treatments were set up to compare different levels of environmental heterogeneity;
  • Some species of Tribolium are cannibalistic Park et al;
  • Most metapopulation models are based on measures of presence or absence in habitat patches interconnected by migration Hanski, 1991, 1994.

With moderate environmental heterogeneity 10 and 30 g of food eleven global extinctions were detected. With low environmental heterogeneity 15 and 25 g of food nine global extinctions were observed. As for influencing growth rates, the simulations performed in this treatment exhibited the same results as those observed in the other treatments Fig. With no environmental heterogeneity, nine coupled populations became extinct. The simulations also showed the same results found in other treatments, including global extinction by four generations Fig.

The treatment in which environmental heterogeneity was highest exhibited the longest time of global persistence Fig. The similarity among them in spite of different treatments may indicate the presence of compensatory mechanisms by Tribolium populations. Tribolium species could utilize cannibalism as a compensatory mechanism when the carrying capacity is not enough to maintain population persistence.

Science lab on the population growth of flour beetles

Cannibalism may change competitive interactions, on one hand, by eliminating competitors and, on the other, by compensating for food scarcity through the nutritional benefits acquired Fox, 1974; Johansson, 1992; Fincke, 1994. There is evidence that cannibalism can facilitate colonization of new environments since cannibals can use intraspecific predation to compensate for resource scarcity in places to which invader species have not yet adapted Johansson, 1996; Wissinger et al.

In a classic study, Jillson 1980 investigated the responses of T. In our experiments there were no fluctuating environments; however, the individuals were moved from a source environment to a sink environment. The present results also suggest that coupled populations with very different growth rates r1 and r2 are more susceptible to stochastic variation, which may contribute to the persistence of populations over a long period of time.

Demographic and environmental stochasticity can strongly affect both local population dynamics and synchrony between them, leading to the deterministic extinction found locally or globally, which may occur due to scramble competition in large cohorts.

  • The pattern of population persistence is shown in Fig;
  • One approach in examining the complexity of these relationships is to experimentally investigate populations under carefully controlled conditions;
  • Of these 50, one bottle received the dispersing fraction and the other received the non-dispersing fraction;
  • Adults were introduced to the medium for one week to oviposit and then removed, thus simulating adult mortality and destabilizing these populations Costantino et al;
  • Theoretical studies have shown that population persistence in patchy environments results from an interaction between local density-dependence, dispersal, and spatial heterogeneity Chesson, 1981; Kareiva, 1990;
  • Global extinctions were observed in all treatments, although different numbers of extinct populations were found for each environment.

Theoretical studies have shown that population persistence in patchy environments results from an interaction between local density-dependence, dispersal, and spatial heterogeneity Chesson, 1981; Kareiva, 1990. Negative density-dependence may cause populations to increase when rare, but positive density-dependence may cause populations to go extinct when rare Amarasekare, 1998.

The main feature of this study was combining migration with environmental heterogeneity, and one of the most interesting results found suggests that stochasticity occurs with more significance in coupled environments with high heterogeneity levels.

Theoretical and empirical studies have revealed that fluctuation in coupled populations may emerge as a consequence of spatially uncorrelated stochasticity in both extinction and colonization events Hanski, 1994. Actually, environmental stochasticity affecting extinction rates is often more or less spatially correlated.

The absence of environmental correlation inherent in environments with high heterogeneity, such as those designed in the present study, probably promotes a significant difference between growth rates in each patch, which characterizes the system as a source-sink, while at the same time causing unpredictable results relative to population growth. We believe that the balance between temporal and spatial environmental variability can determine the level of local population variability and synchrony, with implications for the dynamics of both local and global extinction.

Hence, the global extinction risk can be directly determined by features of local population dynamics. The University of Chicago Press, 782p. Oxford University Press, 449p. Oxford Science Publications, pp.

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