Diversity and Stability in Food Webs : Impacts of Non-Equilibrium Dynamics, Topology and Variation

With progressive climate change, the preservation of biodiversity is becoming increasingly important. Only if the gene pool is large enough and requirements of species are diverse, there will be species that can adapt to the changing circumstances. To maintain biodiversity, we must understand the consequences of the various strategies. Mathematical models of population dynamics could provide prognoses. However, a model that would reproduce and explain the mechanisms behind the diversity of species that we observe experimentally and in nature is still needed. A combination of theoretical models with detailed experiments is needed to test biological processes in models and compare predictions with outcomes in reality. In this thesis, several food webs are modeled and analyzed. Among others, models are formulated of laboratory experiments performed in the Zoological Institute of the University of Cologne. Numerical data of the simulations is in good agreement with the real experimental results. Via numerical simulations it can be demonstrated that few assumptions are necessary to reproduce in a model the sustained oscillations of the population size that experiments show. However, analysis indicates that species "thrown together by chance" are not very likely to survive together over long periods. Even larger food nets do not show significantly different outcomes and prove how extraordinary and complicated natural diversity is. In order to produce such a coexistence of randomly selected species—as the experiment does—models require additional information about biological processes or restrictions on the assumptions. Another explanation for the observed coexistence is a slow extinction that takes longer than the observation time. Simulated species survive a comparable period of time before they die out eventually. Interestingly, it can be stated that the same models allow the survival of several species in equilibrium and thus do not follow the so-called competitive exclusion principle. This state of equilibrium is more fragile, however, to changes in nutrient supply than the oscillating coexistence. Overall, the studies show, that having a diverse system means that population numbers are probably oscillating, and on the other hand oscillating population numbers stabilize a food web both against demographic noise as well as against changes of the habitat. Model predictions can certainly not be converted at their face value into policies for real ecosystems. But the stabilizing character of fluctuations should be considered in the regulations of animal populations.

“A long-term mortality analysis of subsidized firms in rural areas: an empirical study in the Portuguese Alentejo region”

Studies have demonstrated that public policies to support private firms’ investment have the ability to promote entrepreneurship, but the sustainability of subsidized firms has not often been analysed. This paper aims to examine this dimension specifically through evaluating the mortality of subsidized firms in the long-term. The analysis focuses on a case study of the LEADER+ Programme in the Alentejo region of Portugal. With this purpose, the paper examines the activity status (active or not active) of 154 private, rural, for-profit firms in Alentejo that had received a subsidy to support investment between 2002 and 2008 under the LEADER+ Programme. The methodology is based on binary choice models in order to study the probability of these firms still being active. The explanatory variables used are the following: (1) the characteristics of entrepreneurs and managers’ strategic decisions, (2) firm profile and characteristics, (3) regional economic environment. Data assessment showed that the cumulative mortality rate of firms on 31st December 2013 is over 20 %. Interpretation of the regression model revealed that he probability of firms’ survival increases with higher investment, firm age and regional business concentration, whereas the number of applications made by firms has a negative impact on their survival. So it seems that for subsidized firms the amount of investment is as important as its frequency.

Profile and Role of Woman Involvement in Dry System Pig Farming

This research was purposed to study the profile and role of woman involvement in dry system pig farming (pig housing with mattress from grass, pig manure, vegetable waste and kitchen waste).  The research was carried out from August to November 2003.  Pig housing areas were located on eight villages of Kertek District in Wonosobo Regency (Central Java).  The method applied was survey with intensive observation.  Sample were randomly selected, involved 180 respondents (15 percent of total pig farmers), while the locations of the sample were selected based on purposive sampling method.  The result showed that respondents were in productive age, with low formal education level. Most of all are Moslems (98%) and they have small family size.  The level of woman involvement in pig farming was high, approximately 85 percent.  They have other income source and they involve in pig farming to help their husbands in generating income.  Experience in the dry system pig farming was quite long (more than 10 years) and skill come from imitating their neighbours otherwise of autodidact. (Animal Production 6(1): 23-29 (2004) Key Words: Pig, Dry System, Woman Profile and Role

The Use of Pacific Menhaden Oil and Palm Oil on Lipid Metabolism Profile in Blood Serum of Native Cockerels

Cholesterol is an important component of cell membrane, plasma lipoprotein and precursor of steroid synthesis in biologically crucial bile salt and steroid hormones.  Cholesterol level in the blood exceeding the 300 mg/100 ml can result in the incident of cardiac disorder. Cholesterol, HDL (High Density of Lipoprotein), LDL (Low Density of Lipo protein) biosynthesis in the blood plasma of broiler chicken can be manipulated by the use of Pacific Menhaden Oil and Palm Oil.  Therefore, The aim of the current experiment was to investigate the effect of  long chain fatty acid from Pacific Menhaden Oil (PMO) and Palm Oil (PO) use in feed on the blood level of cholesterol, HDL and LDL of native cockerels. Four kinds of ration which contained different levels of PMO and PO were formulated.  They were R0 (control, without PMO and PO); R1 (10% PO); R2  (10% PMO) and R3 (5% PMO and 5% PO).  A total of 72 native cockerels, aged two weeks were kept in 24 pens, three cockerels in each pen.  Each experimental unit were assingned at random to receive one of the four rations in completely randomized designed with six replicates. The use of PMO and PO in feed did not significantly affect (P>0.05) the concentration of cholesterol, HDL, LDL and triglyceride in the blood.  Although statistically was not significantly significant, Cockerels fed R2 had the highest concentration of HDL (39.36 mg/dl) and the lowest concentration of LDL (9.10) in the blood. (Animal Production 7(2): 67-73 (2005) Key Words: Pacific Menhaden Oil, Palm Oil, Cholesterol, HDL, LDL, Triglyceride

Pig’s farmer’s profile in Banyumas Regency

This research was purposed to study pig’s farmer’s profile in Banyumas Regency. The research was carried out since December 1999 to May 2000. It was located at Banyumas Regency.  The method applied was survey with intensive observation, involved 51 respondents (54.26  percent of total pig farmers in Banyumas Regency), consist of 7.80 percent women and 92.20 percent men. The result showed that pig’s farmer were in productive age  (44 years) with low formal education level (Sekolah Dasar). Most of all are moeslems (90,16 percent) and had small family size (4-5 members). They have other income source and they rear pigs to generate income or to use soybean cake’s waste (ampas tahu). Experience in the farming was quite long (more than 10 years) and skill come from imitating their neighbours, friends of other wise of autodidact. (Animal Production 2(1): 40-46 (2000) Key Words: profile, pig’s farmer, Banyumas, experience