3.1. Fundamental Assumption
Building upon evolutionary game theory and incorporating principles of profit maximization and imperfect competition, we formalize the following research hypotheses with key parameters defined in
Table 1.
Hypothesis 1. Within the tripartite Agricultural Industrialization Consortium (AIC), the leading enterprise (LE), family farms (FFs), and integrated agricultural service provider (IASP) constitute a hierarchical Stackelberg game structure. Reflecting bounded rationality: The LE, as the core decision maker, holds the strategy set : {choosing to Initiate the Consortium (probability ) or Not Initiate (probability )}. FFs (strategy set ) and IASP (strategy set ), as subordinate agents, share the strategy space: {Cooperate (probability ), Defect (probability )}.
Hypothesis 2. When all three parties fail to cooperate, each obtains their baseline returns from independent operations. If the core enterprise initiates a consortium while a subordinate party (either the family farm or the integrated agricultural service provider) defaults, the breaching party must provide compensation at a rate of . When a subordinate party chooses to cooperate, it bears a proportion α of the consortium formation cost incurred by the core enterprise, where α represents the cost sharing coefficient. In return, the core enterprise distributes a portion of the cooperative gains to the collaborating party, where denotes the profit sharing coefficient.
Hypothesis 3. Cooperation depth (), with , is a core endogenous variable. This assumption captures the leading enterprise’s dominant role and substantial upfront investment in alliance formation. Its decision on cooperation depth effectively constrains the maximum level of cooperation attainable from subordinate partners, reflecting both structural power asymmetry and resource commitment realities in agricultural vertical alliances. Cooperation costs follow () where k = cost intensity coefficient. This quadratic functional form captures increasing marginal resource integration difficulties prevalent in agricultural supply chains (Table 1). Hypothesis 4. Scale economies activate only under full tripartite cooperation (), amplifying system-wide returns to , where denotes the total factor productivity multiplier. This mechanism explains the empirical necessity of full-chain participation for consortium viability.
This framework extends beyond conventional dyadic models by introducing cooperation depth parameters, formalizing the scale economies’ trigger condition (full cooperation), and modeling quadratic cooperation costs to reflect real-world integration constraints. The agents’ strategy sets are summarized in
Table 2.
3.2. Model Analysis
Based on relevant research [
33,
34], we define the game’s framework by outlining the players’ binary strategies and key decision parameters (see Assumptions 1–4). We then formalize the tripartite evolutionary game payoff matrix (
Table 3). The expected payoffs for the leading enterprise (LE) are defined as follows: we define
as the expected payoff when LE chooses Initiate and
for the expected payoff when LE chooses Not Initiate. The population-averaged expected payoff is denoted
. These payoffs are formally expressed as
The evolutionary trajectory of the leading enterprises (LEs)’ strategies is governed by the replicator dynamics equation:
When
, the system reaches a state of neutral stability
irrespective of the initial proportion x of initiating LEs. Under payoff asymmetry, the boundary equilibria occur at
. Stability at these equilibria is determined by the first derivative:
When , the derivative satisfies and . This establishes as an asymptotically stable equilibrium, demonstrating that LEs will evolutionarily converge to initiating consortia. When , and hold. Consequently, becomes asymptotically stable, indicating systemic convergence toward non-initiation.
For family farms (FFs), the expected payoffs are defined as follows: We define
and
as the expected payoffs for adopting the Cooperate and Defect strategies, respectively. The population-averaged expected payoff is denoted
. These payoffs are formally expressed as
The evolutionary trajectory of the family farms (FFs)’ strategies is governed by the replicator dynamics equation:
The replicator dynamics governing family farm (FF) strategy evolution satisfy the critical stability condition: When
,
for all y, establishing a state of evolutionary neutrality where all strategy distributions are stable. Under payoff asymmetry, the boundary equilibria emerge at
and
. Stability at these equilibria is determined by the first derivative:
When , it follows that and . This establishes as an asymptotically stable equilibrium, demonstrating that family farms will evolutionarily converge to cooperation.
When , and hold. Consequently, becomes asymptotically stable, indicating systemic convergence toward defection.
For integrated agricultural service providers (IASPs), the expected payoffs are defined as follows: We define
and
as the expected payoffs when IASPs adopt the Cooperate and Defect strategies, respectively. The population-averaged expected payoff is denoted by
. These payoffs are formally expressed as
The evolutionary dynamics of integrated agricultural service providers (IASPs) are governed by
When
,
for all z, establishing evolutionary neutrality where all strategy distributions are stable. Under payoff asymmetry, boundary equilibria emerge at
and
. The stability determinant is given by
When , it follows that and . This establishes as an asymptotically stable equilibrium, demonstrating that CSSSO will evolutionarily converge to cooperation.
When , and hold. Consequently, becomes asymptotically stable, indicating systemic convergence toward defection.
3.3. Stable Equilibrium Analysis
Per Ritzberger and Weibull (1995), asymptotically stable solutions of multi-population replicator dynamics must constitute strict Nash equilibria, i.e., inherently pure-strategy equilibria [
35]. Solving the coupled replicator equations
,
,
yields eight pure-strategy equilibrium points:
,
,
,
,
,
,
,
. Thus, asymptotic stability analysis focuses exclusively on these boundary equilibria.
Following Lyapunov’s first method, we evaluate local stability through linearization. The Jacobian matrix J (Equation (10)) governs stability; if all eigenvalues of J possess negative real parts, the equilibrium is asymptotically stable (or an evolutionarily stable strategy, ESS). If any eigenvalue has a positive real part, the equilibrium is unstable (a saddle point) [
36]. Let J denote the Jacobian:
The elements of the Jacobian matrix are defined by Equation (11):
Each equilibrium point is substituted into Equation (11) to derive its corresponding three eigenvalues (
Table 4). Per the Lyapunov stability criterion, all eigenvalues must possess negative real parts for asymptotic stability. Notably, the term
consistently yields positive values, violating this necessary condition for equilibria
and
. Consequently, we focus on characterizing stability conditions for six candidate equilibria:
,
,
,
,
and
. By identifying critical parameter constellations that satisfy stability conditions, we aim to decipher the micro-foundations driving convergence to distinct equilibria and uncover the institutional mechanisms underlying divergent strategic outcomes. Understanding the stability properties of these equilibria yields actionable governance insights.
Scenario 1. When , i.e., when the compensation income is lower than the construction cost, is an evolutionarily stable strategy. In this equilibrium, the system remains stable when the leading enterprise chooses Not Initiate, while both family farms and integrated agricultural service providers choose Not Cooperate. This equilibrium arises because the cooperative surplus compensation received by the leading enterprise falls below the threshold required to cover its construction costs. As a result, low compensation fails to curb opportunistic behavior by family farms and integrated agricultural service providers, while negative net profits reduce the leading enterprise’s incentive to invest in infrastructure. The conflict between individual rationality and collective welfare leads to a state of inefficient lock-in. The compensation coefficient serves as a core control parameter of the system. Once it exceeds a critical threshold, the basin of attraction undergoes a phase transition, destabilizing the Not Initiate–Not Cooperate equilibrium and shifting the strategic space toward cooperative equilibria. The following section employs system dynamics simulations to quantify hysteresis effects near strategic tipping points and identify the minimum compensation coefficient required for Pareto optimality.
Scenario 2. When the conditions , and hold (which indicate a systematic breakdown in incentive alignment), becomes an evolutionarily stable strategy. This reveals a strategic misalignment among the three types of agents: the leading enterprise chooses Not Initiate, while both family farms and integrated agricultural service providers choose Cooperate. This outcome stems from a disconnect in incentive structures. For family farms and integrated agricultural service providers, even considering contract enforcement costs and specialized asset investments, cooperation remains profitable when economies of scale exceed the total cost of cooperation plus the reservation utility of non-cooperation. Market-oriented reforms in factor markets further strengthen scale economies through land intensification and technology diffusion, making cooperation a rational choice. In contrast, if the compensation income received by the leading enterprise is lower than the sum of additional benefits from economies of scale and cooperation costs, the net benefit of Initiate fails to cover alliance construction costs and risk premiums, resulting in strategic suppression. Improvements in factor market maturity and contract enforcement efficiency—specifically, increases in the factor value-added coefficient and the compensation coefficient—raise the probability of strategic shift by the leading enterprise.
Scenario 3. When and , i.e., when the cost of cooperation exceeds its benefits, is an evolutionarily stable strategy. This reflects a strategic asymmetry within the agricultural industrialization consortium: the leading enterprise chooses Initiate, while family farms and integrated agricultural service providers choose Not Cooperate due to unfavorable cost-benefit conditions. For the leading enterprise, even without direct participation from partners, initiating the alliance and obtaining compensation yields higher net benefits than not initiating, thus incentivizing Initiate. For family farms and integrated agricultural service providers, the inequality reveals the core decision making logic: even considering potential shared benefits, expected net returns under cooperation remain lower than the share of costs they would incur under Not Cooperate minus possible compensation from the leading enterprise. Therefore, increasing the profit sharing coefficient, reducing the cooperation cost coefficient, compensation coefficient, and cost sharing coefficient can improve the probability of cooperation by family farms and integrated agricultural service providers.
Scenario 4. When the conditions , and are met (which indicate that parameter values remain below cooperation thresholds), E6 (1,1,0) is an evolutionarily stable strategy. This means the leading enterprise chooses Initiate, family farms choose Cooperate, and integrated agricultural service providers choose Not Cooperate. Inequality analysis shows that increasing the factor value-added coefficient and the leading enterprise’s compensation coefficient does not alter the first two inequalities, but when these coefficients exceed a threshold, the third inequality ceases to hold, prompting integrated agricultural service providers to switch to Cooperate. Moreover, increasing the profit sharing coefficient and reducing the cooperation cost sharing coefficient can also raise the probability of cooperation by integrated agricultural service providers. Their strategic shift, in turn, influences the decisions of the other two agents.
Scenario 5. When the conditions , and are satisfied, again indicating sub-threshold parameters, is an evolutionarily stable strategy. Here, the leading enterprise chooses Initiate, family farms choose Not Cooperate, and integrated agricultural service providers choose Cooperate. The analysis of this case is fully analogous to that of equilibrium point E6 (1,1,0), with the roles and strategies of family farms and integrated agricultural service providers swapped. Therefore, it is not discussed in further detail.
Scenario 6. When the conditions , and hold, indicating optimal alignment of benefits and costs for all parties, is an evolutionarily stable strategy. This represents the ideal cooperative outcome: the leading enterprise chooses Initiate, and both family farms and integrated agricultural service providers choose Cooperate. In this state, the sum of the leading enterprise’s construction costs and shared income is less than its compensation income, while the additional costs of cooperation for family farms and integrated agricultural service providers are lower than their additional benefits, resulting in a stable and efficient cooperative system.